Fraser Cain:  Hey Pamela, are you ready for the Theory of Everything?

Dr. Pamela Gay: I think the correct title for this show is:  AstronomyCast:  the Episode where Fraser breaks Pamela’s brain!

Fraser:  I’ve been looking forward to this show.  We’re going to need another co-host by the end of this show, so if there are any Astrophysicists out there, I intend to shatter Pamela today, so resumes gratefully accepted.

Pamela: And I’d just like to add the disclaimer Observational Astronomist not String Theorist.

Fraser:  [Laughter] Right so at the earliest moments of the Universe there were no separate Forces.  Energy or Matter was all just the same stuff and then the different Forces froze out differentiating into Electromagnetism – the Strong Force and the Weak Force.  

Today we’re going to look at the problem that has puzzled Physicists for generations.   Is there a single equation that explains all the Forces that we see in the Universe and is there some way to put Gravity into it?  Pamela, in preparation for this show, you promised to solve the problem and then win a Nobel Prize for the show.  So how did that go?

Pamela: Um, yeah let’s not talk about that one.

Fraser:  I’m thinking you’ll just come up with it as we go. [Laughter] You’ll go:  “Oh, I know!  Here’s how it works.” Then we’ll sorta spend the rest of the show working on that [Laughter]. Then we’ll send in the application for the Nobel Prize and Sweden here we come.

Pamela: I think I can probably give a half reasonable layman’s explanation of what’s going on, but let’s leave it at that.

Fraser:  Alright.  So I guess the part that’s interesting is we’ve spent the last three shows talking about Gravity, Electromagnetism and the Strong and Weak Nuclear Forces.  How do these Forces come together and how did Physicists work this out?

Pamela: It started as so many things start, with misdirection.  Looking at all the Forces and looking at the history of Physics, people went well; originally Electricity and Magnetism were considered two completely different things. Then Maxwell came along and unified them.  What if we can just continue this trend and just keep putting things together?  

So as we develop this Four-Force theory of the Universe, which seems to work, it was Einstein perhaps who first gave the most stubborn attempt at unifying the Forces.  What he noticed was the Weak Nuclear Force and the Strong Nuclear Force that had one set of mathematical descriptions.  

Gravity and Electromagnetism have their own mathematical formulism.  But when you look at the form for Gravity and when you look at the form the Electric Force, they mathematically have the exact same set up.  

A constant times two qualities of the particles being looked at, in this case either their Masses or their Charges over their separation squared.  He figured that since they must have the same mathematical formulism according to experimentation, then perhaps there is a way to unify these two Forces.

Fraser:  Okay, hold on before you go any further. He understood that both Gravity and Electromagnetism decrease their strength by the inverse square of the distance, right?  So, the further you get the weaker they become at exactly the same rate and that they both have a Constant.  So they just look like they’re the same thing. I could see how anyone could look at that and just think they’ve got to be just two versions of the same Force.

Pamela: As a Physics Prof I’m guilty of teaching the equation for Electric Force and going “look, it’s identical to Gravity” and no it’s not.  [Laughter] What we’ve learned since then unfortunately is Gravity separated itself off first and Electromagnetism sort of separated itself off last.  You really can’t get from one to the other without getting through the Strong and the Weak Force, so he couldn’t get there.

Fraser:  Right.  So how far did he get?

Pamela: He didn’t get anywhere.  He just tried.

Fraser:  But didn’t he like end his life working on this?

Pamela: All because you end your life working on a problem doesn’t mean you’re working on it in a way that leads to anything useful.  It’s a kind of sad state.  In the early parts of Einstein’s career, he made amazing breakthroughs.  But at the end of his career as well as being an amazing mentor to the field and creating lots of quotes that go on posters nowadays, he was spending his time trying to unite two Forces that just refused to be united.  

It was a noble effort and it didn’t work.  The problem that we have is Physics is controlled by sub-atomic particles and he was looking for a more geometric way, a non-particle way to bring these forces together.  

It’s only as we’ve started to extend our understanding of Particle Physics, as we’ve started to discover things like anti-Matter, as we’ve started to think about things that still aren’t testable like Super-Symmetry and String Theory, that we’ve even found mathematical ways to make it conceivable that we can bring these Forces together.

Fraser:  Okay, so it’s almost like there was a whole bunch of additional information that has only since recently been seen with the Big Particle Accelerators and some of the other theories that have shown that the problem is a lot more complicated than Einstein might have thought that it was.

Pamela: That’s exactly the problem.

Fraser:  Right.  How then did Physicists understand that Electromagnetism could be collected together with the Weak and Strong Forces then?

Pamela: The first thing that they had to do was look at the particles that mediate the Forces.  Look at the Bosons.  In this case it’s the 4 Electromagnetism – the Photon that carries the Electromagnetic Force and the W & Z Bosons that carry the Weak Nuclear Force.  

As you crank up the energy in a system, as you turn up the temperature and the density, the Photons and the W & Z Bosons start to have similar energies.  As the Photons have the same Energy as the W & Z Bosons, they start to act in the exact same way.  At these higher energies  – exact same way is probably too strong a way – but they start to act in ways that you can’t differentiate.  

Fraser:  Okay, whoa! [Laughter] Now as I remember you teaching me, Energy and Matter are interchangeable.

Pamela: Yes.

Fraser:  So Photons, which move at the speed of light, can be turned into Matter and anti-Matter at the same time.

Pamela: Yes.

Fraser:  So what you’re saying is that if you increase the Energies of the Matter of the System, you get to the point where the Photons and the Bosons kind of have the same amount of Energy.  If you converted the Photons to Bosons, you’d get the same amount.  Is that right?

Pamela: I wouldn’t say you’re converting anything.  You’re dealing with…

Fraser:  I’m not saying that you’re converting but you’re saying you have an equivalent amount.

Pamela: Yeah.  The Photons are a type of Bosons.  So you have the Photons carrying the Electromagnetic Force and you have the W & Z Bosons – because we named them stupid, you have the W’s and the Z’s – are carrying around the Weak Nuclear Force.  As you crank up the Energy of the entire system, the Photons Energy goes up too.  

Eventually the Photons are carrying as much Energy as the W and the Z Bosons.  Once you get to these super high energies, these super high densities in temperatures you start to not be able to tell the difference between the Electromagnetic Force and the Weak Nuclear Force.  At this point the two Forces start acting as a unified Electro-Weak Force.

Fraser:  Right.  This is the Electro-Weak Force. So where did the Electro-Weak Force actually show up in the Universe?

Pamela: They first started to separate somewhere a little bit before 10 to the minus 10 seconds after the Big Bang so we’re still like way beginning of the Universe.  But, we’re going to go even earlier than this.

Fraser:  So fractions after the beginning of the Universe – the Big Bang – Bang and then you just have the Electro-Weak Force and then moments after that it separates into Electromagnetism and the Weak Force.

Pamela: Yes. The separation starts to occur when the Universe had cooled off.  I love this idea.  The Universe has cooled off to ten to the 27 Kelvin.

Fraser:  It’s merely a one followed by [Laughter] 27 zeroes Kelvin. 

Pamela: And the Energy at that point is a hundred giga Electron Volts.  

Fraser:  Right.  I think the center of the Sun is like 15 million Kelvins.  

Pamela:  It’s a big High Energy….

Fraser:  Yeah, it’s pretty High Energy Physics.  Now we’ve taken the two Forces, mushed them together, and then where does the Strong Force come into this?

Pamela: The Strong Force, we haven’t actually been able to experimentally say can probably been combined in with the Electro-Weak.  But we think it can.  This is where we’re still kinda working on things.  We know there was an Electro-Weak Force, a time when Electromagnetism and Weak were combined.  

We think using what we call Grand Unified Theories that there is an earlier time at a little bit before 10 to the negative thirty-fifth of a second after the Big Bang or so, when the Universe was a mere 10 to the 27 Kelvin, that the Strong Force and the Electro-Weak Force were able to combine using similar mechanisms to how the Weak Nuclear Force and the Electromagnetic Force were able to combine.  

You crank the Energy up, all the Bosons start acting the exact same way and when all the Bosons are acting the same way then all the Forces act the same way – we think.  

Fraser:  If I understand there have been many predictions made by this Theory and so far a lot of these Particles have been detected in the Particle Accelerators that have been used so far, right?

Pamela: This is where things start to get tricky.  We have direct evidence of W & Z Bosons.  They’ve been discovered.  The Gluons that carry the Strong Nuclear Force are a little bit trickier.  We think we have evidence of them.  We say we have evidence of them, but it’s not like we’ve tracked one in a bottle and carried it around.  

The problem with Gluons is they only exist inside Nuclei.  And to get at a Gluon you have to break something into lots of little tiny bits and thus you’ve broken apart the thing that the Gluon lives inside.  

So we see what looks like the Energy of a Gluon falling apart, but it’s a little bit harder to understand how to combine the Physics when we can’t take a Gluon and study it.

Fraser:  This is going to be one of the objectives I guess of the Large Hadron Collider, right?  Crank the Energies up to another level where you might be seeing Gluons all day long.  

Pamela: You’re still breaking apart the things they live within.  You’re still breaking up what we call Hadrons – the Particles that are inside Nuclei.  As long as those things are broken up the Gluons are unstable, they’re just falling apart.  

What the Large Hadron Collider is going to do is find us another one in the missing Bosons.  This is the Higgs Boson.  One of the things that is also kinda broken with our current understanding is we don’t know where Mass comes from.  One of the really troubling things that we have to deal with is why is it that when Electromagnetism and the Weak Force split we ended up with the Photon which has no Mass and we ended up with the W & Z Bosons that have Mass and why is it that the Gluons have so much Mass or Energy however you want to look at it?  

This is one of those things that really confuse us.  We think that it is the Higgs Boson that brings Mass to things.  The more we can learn about the Higgs Boson the more we can understand how it is able to do all the crazy things it does.

Fraser:  The hope is that the Large Hadron Collider will have enough Energy to be able to actually be able to start generating these Higgs Boson Particles so that Scientists will be able to detect them and work the accurate numbers for the Higgs Boson into their calculations.

Pamela: It’s a goal.

Fraser:  Yeah.  All right so this is the Standard Model, right?  We’re kinda up to the Standard Model here…

Pamela: Yeah.

Fraser:  …of Physics where the E^m becomes the Electro-Weak and then the Electro-Weak merges in with the Strong Nuclear Force…I think you said earlier in the show then the first Force to hive? 14:29 off was Gravity.  I’m assuming then that if we just crank the Energy levels even higher the Gluons start to act like Gravitons?

Pamela: Well and here’s where we just don’t know.  We have a Particle Physics understanding of how Electromagnetism works.  We have a Particle Physics understanding of how the Electro-Weak Force works and of how the Strong Force works by itself.  

We’re still working on the Grand Unified Theory that gets us all the way to uniting these Forces together.  But we don’t have a Particle Physics understanding of Gravity.  When we look at Gravity if you follow Einstein’s way of visualizing it, it is a change in the Geometry of Space.  

Now we’re trying to switch over to a Quantum Mechanics view of everything where Force is carried by Particles; where nothing is smooth and where you’re dealing with probabilities and Gravity just doesn’t fit within that way of looking at things.  

As we have been trying to unify the Forces, we have to first find a Quantum Mechanics view of how Gravity works – Quantum Gravity.  We don’t have that.  In order to try and get there people have been going lots of different directions and as near as we can tell the best way to get there from here is perhaps through String Theory.

Fraser:  I’m going to put a line in the sand right now and say up until now we have lots and lots and plenty of evidence.  We’re going to move into pure speculation [Laughter] land.  

It kills us to do it because we love facts-based observational Astronomy but we know that a lot of you are really interested in this subject.  We’re going to move forward into the purely theoretical – the land where there is no evidence there is only theories. [Laughter] So proceed.

Pamela: Well, okay but first let’s start a little bit more grounded in what we actually know.  We have to …….

Fraser:  I drew a line!

Pamela: I know.

Fraser:  We have a line in the sand here. Okay, I’ll let you go back as long as we can go back into crazy land again when we’re done. [Laughter]

Pamela: So we have to start with the Standard Model of Particle Physics and we have to show that it is broken.  When we look at all the stuff that’s out there, all the stuff that’s making you, me, tables, chairs, all that sort of stuff we find there are six happy little Quarks.  

The up and down Quarks conveniently make the Protons and Neutrons which are stable.  They line up in our happy little first-generation part of this chart conveniently with the Electron and the Electron Neutrino all stable themselves.  

Then we end up with a second generation – two more Quarks two more of what we call Leptons.  Electrons and Electron Neutrinos are Leptons.  So we have this generation that includes a Muon and then we have a third generation – 2 more Quarks.  Another Lepton – the Tau Particle and the Tau Neutrino to go with it.  Everything nicely lined up like little soldiers.  

Also matching these we have our 4 Bosons.  We have the Photon, the Gluon, and the W & Z Bosons.  Everything lines up symmetrically.  There’s no reason for this.  This actually led one Nobel Laureate to say who ordered the Tau Particle when it was finally discovered? Symmetries without reason are confusing but we’re about to make it worse.  

In trying to understand how it is that you can combine the Quarks to build Hadrons and how everything has Mass, we realized we couldn’t get there from here easily.  The Higgs Boson introduced a lot of challenges.  The way to get around those mathematical challenges was to then introduce a new Particle to match every Particle we already knew.  

Fraser:  Wait, hold on a second we haven’t even discovered the Higgs Boson yet but Physicists are predicting the Higgs Boson but they already know what their problem is with the Higgs Boson?  

Pamela: [Laughter] Yes.  We’ve had this happen before.  This was actually a problem that was dealt with in the 19^th Century with the Electron.  We couldn’t explain the Mass of the Electron.  There’s just too much stuff stuck into too small an area.  

The way we were finally able to explain the creation of Electrons was through anti-Matter.  Because we have Electrons and Positrons the anti-Matter version of the Electron, it’s possible to figure out mathematically how this stuff, all the Charge, all the Mass into basically a point in Space to create an Electron.

Fraser:  So we’ve got the Matter and we’ve got the anti-Matter and they come together and produce a tremendous amount of Energy or we go the other way, we turn Energy into Matter and anti-Matter.  I don’t understand what that has to do with the Higgs.

Pamela: We basically took and said okay we have all these normal Matter Particles and now we’re going to double the number of Particles by creating anti-Matter and it fixed all the math.  

Then we had the Higgs Boson and we couldn’t figure out how to make it interact politely with all the things that had Mass.  We were kind of confused by things like Photons don’t have Mass and Gluons have a high amount of Energy which is like having Mass.  

This made no sense. The way around it seemed to be to create yet another entire family of Particles.  
Fraser:  So just to make the Higgs work, you then have to predict a whole pile of additional Particles on top of that.  So, it’s almost like they all come together.  

You get the Higgs and then you get some other Particle that makes it work and the only way you can have that Particle that makes it work is have a whole bunch more particles.  

Pamela: Yes.  We’re okay with this.

Fraser:  [Laughter] Okay with this, all right.

Pamela: [Laughter] This is actually something that sort of kind of maybe makes predictions that are provable.  The Super Symmetric Partners – the Spartners have sort of kind of predicted Masses and the lightest of them is something that we like to blame Dark Matter on sometimes.  

It’s possible the lightest of these Super Symmetric Particles might be something Large Hadron Collider could get at.

Fraser:  So would there then be an equivalent – you went through all the Particles in all their happy shapes and all lined up like they’re little soldiers – there would be Symmetric Particles for all of those?

Pamela: Yes!

Fraser:  Right and including the as of yet undiscovered Higgs.

Pamela: Probably.

Fraser:  But like what does this have to do with Gravity?

Pamela: Now we’re trying to figure out how to mathematically describe all of this.  In the process of trying to describe all of these Particles, Scientists struck on the idea of what if Particles are nothing more than Strings that are oscillating in different ways and the way they oscillate defines the different characteristics of the different Particles. 

This is where the math gets scary.  It’s out of trying to come up with the math that describes all of these different Particles that as you start to try and figure out how to build a Proton out of Quarks?  How do you build Neutrons?  How do you build what we call Hadrons?  

Protons and Neutrons are Hadrons.  In the process of trying to figure this out, they ended up with this weirdo Particle that had a set of characteristics including no Mass that wasn’t generally useful unless it just happened to be the Graviton.  It actually sorta fell out of the math that you could build using String Theory a Particle that led to Gravity.

Fraser:  Oh, okay let me have another shot at this.  In creating that whole collection, that Super Symmetrical set of Particles you got one Particle in that that could work for Gravity.

Pamela: Once you start to try and figure out how to build Neutrons and Protons out of Strings.

Fraser:  I see so it’s like if you can use this method where the math seems to work that allows you to build Protons and Neutrons out of these Particles, one of the happy side effects is that it also helps to explain Gravity.

Pamela: Right.  There are lots of other things that are falling out of these theories.  We start to end up with weird characteristics like the Proton, the thing that basically Atoms need in order to act like happy Atoms.  Protons decay eventually so there’s this possibility that in like ten to the 44 years or some obnoxiously large number like that Protons will start decaying in the way that like Uranium breaks down into other different things.  

Except in this case the Protons are breaking down into Energy.  This sort of causes things like those Black Holes and White Dwarfs and Lone Solid Planets without Stars that are the only things left after the Energy Death of the Universe.  They start evaporating.

Fraser:  Yeah, I know we talked about that a bit in one of our shows.  The Large Hadron Collider for starters should be able to, if we’re lucky, detect some of those heavier particles and maybe put some parameters on the Super Symmetry. 

 On that whole other collection of Particles that mirrors the Higgs Boson.  So, find the Higgs Boson and then find the Symmetrical Particle for it and maybe keep going up the chain.  Is that right?

Pamela: Yeah, that’s unfortunately the fate we have and none of the things that we know about currently will help us really understand is this String Theory or is this just a really ugly Particle Universe where these are all just stand-alone little Particles.  

Fraser:  I think that without you actually going into the math of String Theory, I hope that gives people the understanding of where String Theory comes from.  It’s a way to mathematically solve the introduction of these Super Symmetrical Particles.  

One of the happy outcomes of that is that it might predict how Gravity works with the rest of the Particles.  So is there sort of a whole other line of thinking?

Pamela: Right now, String Theory is the direction everyone is going in.  There are people who are thinking Super Symmetry doesn’t require Strings.  We don’t really have any other alternatives.  There’s a bunch of different flavors of String Theory but it really all boils down to strings.  

There are a lot of people – myself included – that are just kind of hoping that maybe some young genius will come along a new way of visualizing the Universe that might open our eyes to some sort of creative idea.  

We’ve been working on String Theory since about 1970.  There hasn’t been a major breakthrough the way Einstein said “let’s look at everything in terms of Geometry.”  We need that young genius to think out of the box and think creatively to bring all the pieces together.  

Fraser:  As I understand String Theory is going to be almost impossible to observe observationally.  

Pamela: Right.  There are a few predictions like Cosmic Strings fall out of some of the theories and the Cosmic Strings and String Theory – the use of the word String its different strings in these two cases.  

In the case of Cosmic Strings you end up with basically this high, high density line through Space where it’s basically a line where the dimensions don’t line up right. Sort of like when you get ice cracking as it freezes in a lake.  

In this case as the Universe solidified out and ended up with these faults in its structure.  It’s possible that these things exist and we might someday detect one.  There were a couple papers a few years ago of possible detections but none of them ever panned out.

Fraser:  Right as I recall these are where you might get the first moments after the Big Bang magnified in the structure of the Universe as the Universe went through its inflation and expanded any little changes, permutations would just get blown up, really magnified into the Universe, right?  You can see it.

Pamela: Right.  There are people who have predicted that if you build a telescope that has a thousand square kilometer surface area that works in the Radio, maybe you can detect other features in the Sky.  But, that’s a telescope we don’t exactly have the resources to build.

Fraser:  Yet.  [Laughter]

Pamela: Okay, so if we go and grab an Asteroid, tear it apart and turn it into a Radio telescope…right now we’re not there.  So right now we have no way to tell all of these different proofs apart.  It’s frustrating. 

Fraser:  So, in other words there are apart from Super Symmetry there are no really serious attempts to unify Gravity and the other Forces.

Pamela: This is the direction we’re going in right now – for better or worse.

Fraser:  That’s why billions have been spent to build the Large Hadron Collider and hopefully within the next couple of years, new Particles will freeze out of the energies and we’ll be able to see them.

Pamela: And what’s cool about that Large Hadron Collider is it could always turn up something we never predicted forcing us to rethink everything but giving us an experimental starting point.  And that’s just cool.

Fraser:  You know, I don’t think you were able to come up with something brand new that would win this show the Nobel Prize.  

Pamela: No, I’m much happier with telescopes than I am with math.  

Fraser:  Well then we’re going to get the Nobel Prize with something having to do with telescopes. [Laughter] We’ll go to Sweden eventually.  Thanks Pamela and thank you for wrapping your head around this. I really hope that this was able to give people some access to what the direction of the cutting edge of the Physics is going in. 

It’s not easy to understand.  I don’t understand it.  You barely understand it and you’re in it. [Laughter] I really look forward to everything that comes out of Large Hadron Collider and the Physicists working there.  I can’t wait.

Pamela: And I know we’re going to get letters on this one.  If you want to know more go read Brian Green’s book, “An Elegant Universe.” If you are a String Theorist, we’re sorry.

 

Download the transcript

Fraser Cain:  When you were in the middle of doing your live show at Dragon Con, I was moving.  We’re all moved in, lots of boxes all over but I’ve got Internet so that’s all that really matters.

Dr. Pamela Gay: Does anything else really matter?

Fraser:  No, just the Internet.  Thank you for doing the Dragon Con Live recording.  That was really cool to have Phil and Dr. Grazier.

Pamela: Next year we really will have you there even if I have to kidnap you.

Fraser:  That’s fine, sure.  I’ll come.  Let’s move on then.  We have a big surprise coming which if we can get ourselves organized and then it will just show up in the feed.  That’s all I’m going to say on that.  

After a quick Dragon Con break, we’re back to our tour through the fundamental forces of the Universe.  We’ve covered Gravity and Electromagnetism.  Now we’re moving on to the strong and weak nuclear forces.  We didn’t think they would need separate episodes so we’re going to put them together.  

Then we’ll cap the whole series off with our quest for the search for the theory of everything and that’s when we win our Nobel Prize. [Laughter] I can’t wait.  I hear Sweden is very nice this time of year so I’m really looking forward to that.  So where do you want to start, strong or weak?

Pamela: Let’s start with strength.  Let’s start with the Strong Force.  

Fraser:  Okay, now what is the Strong Nuclear Force?

Pamela: It’s essentially what holds the nuclei of Atoms together.  If you’ve looked at a Periodic Table recently you’ll notice that it starts to get a little fuzzy around Element 100 or so.  As you start to get these really big nuclei, the Strong Force isn’t quite strong enough to hold everything together.  For smaller Atoms, it does a very good job it is in fact one of the strongest forces we have out there which is why it is called the Strong Force.  

What it essentially does is to cause little particles; Gluons in this case, fly back and forth.  As they fly back and forth, they glue the different particles together. This is an extremely useful thing because otherwise Protons and Neutrons really don’t have any reason to stick together with the Electrostatic Force.  One is charged the other is neutral.  You have to have some other force to hold these pieces together.  

Fraser:  Right, so at the center of the Atom, you have your Protons and your Neutrons and they are being bound up together by the Strong Force.  But not Electrons, right?  

Pamela: No, the Electrons come in using strictly Electrostatic Force.  

Fraser:  Okay.  I know you can break up Protons and Neutrons into more elementary particles.  Is the Strong Force holding those elementary particles together as well?

Pamela: This is where we start to get into a sub-part of the Strong Force sometimes referred to as the Color Force.  Protons and Neutrons are made up of different flavors of Quarks.  You have up and down are the two stable Quarks that go into making pretty much everything around us stick up.  So your Protons and Neutrons are both made up of combinations of up and down.  

The Color Force is part of what gets in as its own form of the Pauli Exclusion Principle.  You have this idea with Electrons that you can only have a spin up and a spin down orbital.  If any of you have taken Chemistry, this is what explains the entire crazy orbitals of Atoms thing that you had to memorize in tenth or eleventh grade.  

With Quarks you have the same thing going on where you can’t have three Quarks that are the same color all in one Proton.  Instead you have to have combinations of colors.  Just for the sake of having names they’re generally referred to as primary colors but they’re not a real color.  There’s no real color involved, we just needed a word.  

So instead of making up a word, we decided to abuse a word. With the Strong Force we have the Protons and Neutrons are all made up of Quarks and the Quarks are held together with the Color Force which is part of the Strong Force.

Fraser:  Now you said that there are Gluons zipping back and forth between the particles and that’s what is communicating the Force, right?

Pamela: And this is actually also what limits the Force to such a short distance.  Gluons have mass and because Gluons have mass the Heisenberg Uncertainty Principle which says you can either know where something is or how fast something is moving and it gets involved in other things.  

It says that once you end up with something as heavy as a Gluon you’re limited in how far you can go, how far you can interact to about ten to the fifteenth of a meter.  So, that’s a zero followed by fourteen more zeros and a one.  Zero point 14 zeros 1 meter is the distance at which a Gluon is capable of holding things together.

Fraser:  And Gluons have actually been isolated in Particle Accelerators, right?

Pamela: They were first detected back in 1979 and since then we have been turning them up in various different places.  Stanford Linear Accelerators played with them; Brickhaven National Laboratories has played with them. All sorts of different Colliders and Accelerators have played with them. We know they’re there.  We can quantify different characteristics about them.  This part of Physics we’re quite certain about.

Fraser:  So if you then were able to intercept Gluons that were communicating back and forth between a Proton and a Neutron they would fall apart if you were able to sort of siphon away the Gluons?

Pamela: Well that’s kind of the wrong way to think about it.  All these things that are communicating for us can also exist independently.  For instance with the Electromagnetic Force that we covered a couple weeks ago, you have Photons moving back and forth.  

In some cases we refer to them as Virtual Photons because you don’t really see them.  It is these Photons that are communicating with the Electric Fields and the Magnetic Fields.  

Photons can get shot out of a laser beam and they are quite happy to exist as stand-alone particles.  If you create enough energy in some sort of collision then out of that energy you can start to get particles just materializing.  So, in this case we have something with a mass that is a little bit less than a few mega-electron volts.  

We just need to collide something so that you end up with more energy than that with the correct decay rates where you end up with Gluons as part of this energy condensing down the stable particles.  They can exist without having to be trapped inside of a Nucleus.

Fraser:  Right.  So what is the strength of this Force compared to say Gravity?

Pamela: In general the way we talk about Forces, it’s easier to not say, “this has this many Newtons of Force.” But we instead look at the relative strengths of Forces.  So, let’s say, because it’s true, that the Strong Force is the strongest of all the forces.  Well, then the Electromagnetic Force between two particles that are nearby compared to the Strong Force it has a strength of one one hundred and thirty-seventh of that.  

So if you stick two Protons next to each other in the Nucleus of an Atom, the Strong Force holds them together with a Force we’re going to call one.  But at the same time because they’re both Protons they’re trying to repel each other.  Likes repel likes in this case.  

The Force that is trying to push them apart is one divided by one hundred thirty-seven times smaller than that Strong Force.  Now, at the same time, if Gravity is trying to hold those two Protons together, here we get into ridiculously small numbers.  

Those two Protons trying to push each other together compared to the strength of the Strong Force holding them together is six times ten to the negative thirty-ninth.  So, you take a zero and you take a one, you put thirty-eight zeros and then a six and that is how much weaker this Force is.  

Fraser:  Right, and so the equivalent to think of an analogy is like you have magnets with two pointing towards North, you take the two North sides of your magnet and just jam them together.  [Laughter]  You can hold the magnet together with the force of your arms.   

You can overcome the Magnetic Force there and then as soon as you let go of the magnet they pop away from each other.  Even though Gravity is pulling the Protons together, the Electrostatic Force is pushing them apart.  The Strong Force is dominating it and it’s the thing that’s really holding them together.  

Pamela: Here there reason that we’re able to see Protons repelling each other at other distances is as soon as you get past that ten to the negative fifteenth of a meter the Protons no longer care about the Strong Force.  So in order to build the Nuclei of Atoms you have to get within this very limited distance. 

You have to slam the Protons together the same way you might slam two magnets that are trying to repel each other apart together.  Once you get them close enough, the Strong Force overcomes.  

Fraser:  We’ve covered the Strong Force, so why don’t we switch over and learn about the Weak Force, what is it?

Pamela: The Weak Force is how we look at Atoms and we observe them decay and we had to explain this somehow.  What is it that is causing all of a sudden one Atom decides it is going to transform itself into something that has the same number of stuff in the center, the same number of Protons plus Neutrons in the center?  

But all of a sudden, one of the Protons decides it is going to become a Neutron and thus the Atom changes names while maintaining very close to the same weight.  This is beta decay.

Fraser:  Give us an example of something that might decay.

Pamela: For instance if you have a Plutonium 15, this is one of the things that crops up in all sorts of different radioactive experiments.  That will end up decaying to Strontium 16.

So, you’ve changed the number of Protons, increased the number of Protons, decreased the number of Neutrons and along the way you’ve given off an Electron and you’ve given off an Electron Neutrino.  This helps keep everything balanced out.

Fraser:  Right.  The amount of energy in the whole system stays the same.

Pamela: Charge is conserved so you went from the Neutron to having a Proton and an Electron and then there’s an Electron Neutrino to help things out.

Fraser:  So the math works; like you could sit down and add up all the particles before in the energy and add up all the particles after in the energy and it all balances back out again.

Pamela: Just to get the details correct, it is an Electron and an anti-Electron Neutrino.  Those two come in pairs together.

Fraser:  Right, but I guess the question then is why?  Why does this just spontaneously go ‘pop’? [Laughter] And then you have a completely different element.

Pamela: It’s the constant quest to find the lowest possible energy level.  Neutrons in general aren’t the most stable of things.  If you leave a Neutron alone on a shelf for fifteen minutes it will decide it wants to be a Proton, and Electron and an anti-Electron Neutrino.  

It’s kinda hard to leave a Neutron alone on a shelf but if you could, and they do this in various types of experiments, in Atoms usually states that have lower energy are better balanced.  It gets a better distribution of particles in the center such that it is at a lower energy level.  

In the quest to achieve the lower energy level, you end up with Protons changing over to Neutrons or sometimes the reverse.  It depends on the particular reaction.  It just happens to be that it is the Weak Force that makes this happen.  What’s actually happening is that you have Quarks changing from up to down.  

So, as you go from that Plutonium to that Strontium, what is happening is one of the down Quarks transforms into and up Quark.  That gives us the Neutron going into a Proton and it’s that change from down to up that is triggered by the Electro Weak Force. 

Fraser:  Then how was the Weak Force discovered?

Pamela: There is first of all just the fact that WOW we have things decaying.  We have different particles where we see Electrons coming off; we see the nature of the Atoms changing.  Radioactive decay happens and so we had to explain what was going on.  

As we built the standard model of Particle Physics where we saw that Protons and Neutrons are made up of Quarks we realized that somehow a Proton had to change into a Neutron or vice versa depending on the particular reaction.  

This meant that somehow we had to conserve all these different qualities and we needed something to mediate all of this and that’s where we started looking for the Weak Force.  It actually wasn’t until the 1980s that we finally started to be able to find the particles that mediate all of this.  That’s the amazing thing about this, for most of our listeners. This is stuff that has happened in all of our lifetimes.  

In the case of the Weak Force, it is moderated by what we call Vector Bosons.  In this case they have masses of greater than eighty giga-Electron volts which is a lot, not that people tend to think in giga-Electron volts.  This large mass, this mass that is a lot bigger than the mass of the Gluons that mediate the Strong Force means that this particular Force only acts over distances smaller than a Proton.  It can only affect things at the particle size.  

What are mediating this are the W and Z Bosons.  So we again have Bosons and these Bosons were detected in the 1980s, again by creating really high energy experiments where the energy fell out into a variety of different particles that in the cascade of energy and the stable particles along the way the Vector Bosons became apparent. 

Fraser:  That seems quite amazing to me that you could perform the big collision, freeze out the energy into the particles and then have a particle bounce against one of your detectors and then say: “Hey you know, that’s probably the particle that communicates the Weak Force.”  [Laughter]  

I’m trying to think how they would do that.  Did the Scientists then in their calculations from one of their theories say, “if a particle of this amount of energy and mass bonks against your detector that’s what it has to be”?

Pamela: It’s actually even more subtle than that. What you do is you collide things violently inside of a detector.  Often you’ll end up with essentially donut shaped accelerator rings. You have two rings running parallel to each other except the particles in one are going clockwise and the particles in the other are going counterclockwise.  

Then you feed them together inside of your Detector such that you’re forcing two different streams of particles to collide inside your Detector.  Then as this amazing release of energy where you have the energy that is in the mass and the energy that is in the velocity of these particles all coming together.  This energy then freezes back out into a cascade of particles that in many Detectors are now moving through magnetic fields that have been put in place.  

How the particles move through the magnetic fields is a function of what is their mass, what is their velocity and what is their charge.  By looking at what are often really neat curly Qs, what are really neat bent paths through these magnetic or electric fields, we’re able to backtrack through well, this seems to have had this reaction time. We can figure out the velocity it lasted this long.  It curved this much in that amount of time which means it probably had this amount of charge.  

We look at all of these different characteristics and look at how they moved through the Detectors in a variety of different ways.  Sometimes fiber optics is being used; sometimes you’re doing this in gases.  There are all different ways that you can detect these different particles. 

It’s by looking at their paths at different points that we’re able to work out what the masses had to have been, what the charges had to have been and figure out what it is exactly that we’re looking at.  Sometimes we’re not entirely sure.  There’s been some, “well it could have been”, observations of something that might have been the Higgs Boson but no one believes the results.  

We know that there’s something there but we’re not positive what it is because the results weren’t solid enough.  There weren’t enough particles produced, there wasn’t enough signal in the Detector…It’s a frustrating game.  

It took until I was an undergrad at Michigan State for the final of the Quarks to be found just because it was such a massive particle that trying to get enough energy to generate it is a cascade effect.  You can’t just say “I need this many giga electron volts”, and it will create a top Quark.  You have to overshoot and see what falls out of the energy that condenses down.

Fraser:  Well we’re only about a week away from them firing up the Large Hadron Collider and the search for the particles begin and not the destruction of the Earth.

Pamela: No, Earth is not going to be destroyed.

Fraser:  It’s a search for particles.  I guess the question is, how are they connected?  They’re both called Nuclear Forests.  

Pamela: At extremely high energies, things start to all unify.  We’re still trying to understand all of this.  There are so many things about Particle Physics that we’re still working to try and understand.  

With the Standard Model of Particle Physics as you move toward higher and higher energies, there seems to be a point and a density at which things are crammed together to the point that you achieve the energies that go through the Strong Force and the Weak Force combined and act in one way.  

But at this point you also sort of have the soup so talking about individual Atoms starts to get trickier.  This is how we’re slowly trying to move towards a grand unified theory.  This is something that we’re going to talk about more next week as we start to talk about how we’re going to get our Nobel Prize, which really we won’t.  We’re just going to sorta repeat what other people have said.

Fraser:  Hey, that’s quitter talk! [Laughter]  We are so going to get a Nobel Prize.

Pamela: Right now what we talk about is the Electroweak Unification and there actually has already been a Nobel Prize for this.  We discovered the WZ 22:33particles, the Intermediate Vector Bosons that convey these Forces back in 1983.  

There is a Nobel Prize given to Weinberg, Salam and Glashow – I have probably mispronounced their names terribly. Weinberg is the only one I’ve met, so the other two haven’t told me yet how they say their names.  

It’s thought that at high temperatures where the energy of all these particles colliding one against the other against the other is about 100 giga electron volts.  At these extremely high energies, the weak and electromagnetic interactions all start to be a manifestation of a single Force.  

We’re still working to try and put these things together.  Our basic picture is at energies where Quarks start to be their own separate happy little particles we have four Forces acting completely separate from one another.  

But, as you start to get to energies of about one hundred giga electron volts, which we actually had when the Universe had a temperature of – and pardon the scientific notation – about ten to the fifteenth Kelvin.  You don’t say degrees because Kelvin is its own special thing.  At one followed by fifteen zeros Kelvin the Universe was so hot and so dense that the Electromagnetic and the Electroweak Forces combined into one Electroweak Force.  This occurred when the Universe was a little bit younger than ten to the negative tenth of a second.

Fraser:  So, early on.

Pamela: Yeah. [Laughter] Well before the first second it was done transpiring.  By second one yeah, everything was nice and happy and we had Quarks were separate and all the Forces were separate.  

But early on at that little less than ten to the negative tenth of a second, we only had three forces:  the Electroweak, the Strong and the Gravity.  Now if you keep going a little bit further back in time and get to so it’s about ten to the 27 Kelvin, at that point we start to be able to bring the Electroweak and the Strong Force together as well.  

Where we get lost is when we try and bring in Gravity.  The details of how you unify the Electroweak and the Strong Force we’re really not so sure on, but we’re pretty sure it happens.  We’re working to try and build a model that explains magnetism, explains electricity, explains Beta decay, and explains how it is that the Nucleus itself holds itself together and why it is that we don’t end up with Atoms the size of the Solar System.  Why is it that we have a finite size to the nucleus of an Atom?  The finite size of the Nucleus of an Atom comes from the Strong Force having a limited distance.  

The Beta decay comes from the Weak Force. Electromagnetism is what brings the Electrons and the Protons together and allows molecules to form and allows refrigerator magnets to adhere themselves to refrigerators.  One of the neat side effects of trying to unify these three Forces, the Electromagnetic, Weak and Strong Forces is pretty much all of the theories out there predict that Protons decay.  There is no observational evidence for this.  

In fact, all observational evidence points towards Protons really not wanting to decay.  If they do, they do it over extremely long lifetimes.  But if Protons do decay and our current ideas on how you might unify these three Forces are true, then trillions of years from now when all the Stars are dead, when all the Black Holes are sitting there happily evaporating away.  When maybe there are one or two dead cold White Dwarfs floating around but maybe not.  Everything that is left, any Protons that are out there are going to start to decay. 

That means that even any Rogue White Dwarf Stars that just might happen to have survived are going to evaporate.  Any Rogue Planets that might have survived are also going to decay away as the Protons simply become energy.  

That’s even a more depressing future than some of the ones we’ve looked at before, but we don’t know if this is true.

Fraser:  I think it’s equally as depressing. [Laughter] 

Pamela: You think so.

Fraser:  I think they’re really just exactly the same, yes.  [Laughter]  Okay, well and you’re already starting to ruin next week’s shows.  I have to stop you.  

Next week we will talk about the quest and the discoveries that were made and that were to bring everything together.  We’ll probably have another look at String Theory just because that’s part of it.

 

Download the transcript
 

Fraser Cain: Let’s get on with the show then. Everyone seems to like our series, our tour through the Solar System, our information about Mars. We’ve got a new series for you. I think people keep wondering about when we are going to run out of topics. Well, here you go.
 
We’re going to handle all the forces of the Universe and this week we’re going to do gravity. We haven’t covered that show yet and here were are a hundred plus shows in. We’re going to start with gravity, which is a force you’re most familiar with. We know gravity happens when masses attract one another and we can calculate its effect with exquisite precision.
 
However, you might be surprised to know that scientists have no idea why gravity happens at all. Pamela, let’s go back and just image you’re in your class and you will be presenting gravity to people. Where do you typically start?

Dr. Pamela Gay: I usually drop something loud because that gets their attention. But I won’t do that to our pod cast listeners because [Laughter] that might be cruel to their eardrums if they’re wearing headphones.

Fraser: Preston, resist the urge to make a loud noise. [Laughter] He’s our Editor. Okay.

Pamela: The way that we’re most aware of gravity is things fall. We fall. We fall upstairs, downstairs and you always fall toward the center of the Earth. Keys fall, books fall, and I’ve fallen off of horses. Falling is one of these things that people have been aware of since they first stood up.
 
The question is why? Why is it that I always fall toward the ground and not toward the sky? Why is it that people on the North Pole and the South Pole both stay adhered to the surface of the planet and don’t go flying off into Outer Space?

Fraser: You can imagine that gravity is such an all-pervasive force that ancient peoples almost didn’t even think about it. You know? It’s also like why when I breathe is there air in my lungs?
 
It’s because gravity is holding the atmosphere next to the planet. But it’s not something that you would even consider. So when did people start to realize there was something going on?

Pamela: It was often addressed as a philosophical question. Why down and not up? Why don’t we go into the sky? This became even more troubling when we discovered the planet is round.
 
Galileo did our first scientific investigations of gravity. Everyone has heard the stories of Galileo dropping things off the Leaning Tower of Pisa. No one knows if that actually happened. If it happened, he certainly didn’t document it. Galileo was one of these people who documented everything.
 
But, what he did do was roll balls down inclines, which doesn’t sound all that exciting but prior to Galileo’s investigations we had Aristotle’s ruling the days ruling the day saying that objects started in motion always come to a stop. Everything comes to rest.
 
That was the way we viewed the Universe because friction does cause everything on the planet Earth to generally stop. But Galileo, through very careful investigations, realized objects of different masses, shapes and sizes only fall differently as a result of how they interact with air.
 
He realized that if you have an object moving across a smooth enough surface and it goes down an incline, it would go up an incline to the exact same height on the other side. He was able to start saying, gravity is this thing that is causing the ball to go down the incline and the go up the other side.

Fraser: Now as I remember Galileo used ramps as a way to slow the whole process down. That is was impossible to measure if you just drop things but if you put things on very slanted inclines there was a way that he could actually start to measure how long things were taking to drop.

Pamela: He was actually using water clocks. This was a really cool way to basically say if you have a bucket filled with water with a little tiny hole in it and there is a large enough surface area to that bucket – because surface area plays a role in how fluids flow – and it’s a short enough period of time then you open up the spicket on the bucket and let the water start dropping out into the Galileo equivalent of a graduated cylinder. You measure the volume of water that comes out while the ball is rolling down the incline.
 
It’s a surrogate for measuring time. If you assume that one drop of water falls per one second and you can figure out the volume of one drop of water, the volume becomes a measure of time. He was able to figure out this acceleration measurement for how balls fall down. They have this speed for the first second, this much larger speed for the second second; an even larger speed for the third second.
 
He was able to figure out all of this related to the angle of the incline, all sorts of really cool math. He did all of this using a water clock that he basically started and stopped by starting and stopping the water.

Fraser: And so the conclusion that Galileo came to was that the force of gravity is acceleration. I guess people always intuitively understood that. You fall off of a higher drop and you’re going to get hurt worse. [Laughter] But I don’t think they realized exactly how that worked.

Pamela: One of the coolest things about what Galileo did was he put together the whole notion that any two objects should fall at the same rate once you take into account air resistance.
 
This had actually been somewhat confusing before because if you imagine a barbell falling, if the rate at which something falls is a function of mass then if you replace the bar in the center of the barbell with a piece of string how does that know to fall at the same speed as the two bars connected solidly versus why would two balls without a string between them fall at a completely different rate.

Fraser: Right and you can always go back to that example of a ball versus a feather, right? I guess they thought that the feather was lighter and so it would fall more slowly while the ball would fall more quickly.

Pamela: Yes, and then you extend this idea out to small child falls slower than large man. Please don’t do that experiment. It didn’t really make sense though when you consider how does a man holding a child fall? Don’t do that experiment either.
 
Galileo basically determined it was just air, its okay and moved on. We still don’t know why though. This not knowing why was a problem that we continued to have for a while. Kepler came along and figured out equations to describe the motions of the planets. He didn’t know why they were doing it but we had equations.
 
Galileo described mathematically how objects go down inclines and go up the other side but didn’t know why. It was Newton who came along and according to the story saw an apple falls…

Fraser: Did this really happen – oh, he didn’t get hit on the head, right? [Laughter]

Pamela: No, apparently not. I mean, who knows? But according to the story Newton saw an apple fall, looked up and saw the Moon and decided that the Moon was falling. It was probably a more complicated train of logic.
 
He worked out that if the Moon was so far away and a certain size – well we don’t really need the size that much – but if the Moon is this far away, and the apple is this far away and we look at how they’re falling and the Earth is this size…..
 
Using lots of cool mathematics that you can actually do with basic algebra, he was able to figure out that the Moon was just falling around the planet and managing to miss it as it goes.

Fraser: I remember the thought experiment for this was where you imagine that you have a cannon and you’re firing it sideways and the ball hits the ground a few hundred meters away. Then you tilt the cannon back and you have much more powerful cannon and you shoot it and the ball will land further downfield.
 
You eventually get to the point where the cannon is strong enough that the ball just goes all the way around the Earth and lands back on the guy who fires it. Eventually you can keep shooting it harder and harder until the ball just goes all the way around and it’s falling but it’s like the Earth just keeps moving out of the way.

Pamela: Newton was able to take that idea and go: “Oh, Moon falling; oh, Earth falling around Sun.” All of a sudden what we see is everything is falling but the curvature of its fall doesn’t allow it to ever make it to the object it is falling toward. That is a kinda neat image and he had really neat math to go with it.
 
Then unfortunately there are things like oh, the planet Mercury that screwed things up. It was all well and good; we were able to find Uranus because of Newton’s applications.
 
There were two different scientists, two different mathematicians one in England who did lots of equations and threw out lots of possibilities and one in France, who basically did one calculation, threw out one possibility.
 
Then an observer went out and looked at the Frenchman’s coordinates and discovered a new planet. All of a sudden Uranus’ orbit made sense. But, Mercury’s didn’t so we waited around trying to figure out what is wrong with gravity.
 
Then Einstein came along. Einstein was able to give a reason for gravity existing. Look at gravity as a curvature to the Space Time Continuum.

Fraser: Whoa! Explain that.

Pamela: Yeah, I know, it’s a kinda big jump.

Fraser: Like I’m sure people thought well that was helpful. [Laughter] Thanks Einstein.

Pamela: Yeah, he just sorta reformulated how you’re supposed to visualize all of everything. He came along and said basically imagine Space as more dimensions such that the gridlines of our three-dimensional grid get tightly packed as you get closer to the Sun because you’re falling in toward the Sun.

Fraser: I think the analogy we always use is like a rubber sheet with a bowling ball on it.

Pamela: You can imagine that in our flattened Universe, our flattened Solar System, the Sun creates a deep pocket in our plastic sheet of Space. If you’ve ever seen crazy skateboarders, they can get themselves going around the edges of bowls.
 
If you watch crazy bicyclists, they’ll get themselves going around the inside of velodromes which are curved surfaces. You can imagine the planet Earth as it rolls along Space moving around the rim of some sort of Cosmic Velodrome where it is the Sun that defines the center of the particular curve that we’re orbiting around in.

Fraser: Just to backtrack for a second what exactly was the problem with Mercury?

Pamela: Its orbit wasn’t going at the correct rate. We have an entire show on Relativity that people can go back and listen to that brings this up. Basically the problem is that its orbit precesses in a way that we couldn’t fully account for.

Fraser: Ah, and the word precess?

Pamela: That means that it’s an ellipse and where the end of the ellipse is changes over time.

Fraser: Okay, no I see. You’ve got like an oval like a loop and Mercury is going around the loop and you’re sort of tracing this oval but the oval’s position is slowly rotating like a Spirograph.

Pamela: Yeah, the kid’s toy.

Fraser: Okay and so the position of where that oval of Mercury’s orbit was supposed to be didn’t match up what Newton had predicted. And Einstein said that’s because of Space Time Continuum and all that junk.

Pamela: Right and then some mathematician came along and beat them with a stick and said it’s an ellipse not an oval because mathematicians like to do that. So we have this problem with Newton’s understanding of gravity and Einstein came along and announced he had a new formulation. It’s all a curvature of Space. Gravity is nothing more than geometry.
 
The problem is gravity breaks at the beginning of the Universe and in centers of Black Holes. Things just get so dense that infinity signs start popping up and dividing by zeros starts popping up and much badness occurs.
 
About the time that people decided this is bad and math can’t handle this, we also started building a standard model of particle physics where we look at other forces – which we will talk about in succeeding shows – such as electricity and magnetism, which is the electromagnetic force.
 
We started looking at them and realized there were photons, particles of light! They carry these forces. They cause the electric force they cause the magnetic force. The electromagnetic is one force.
 
We realized other forces, the weak force, the strong force, also had little particles we call bosons that walk around at extraordinarily high speeds and carry the force with them and communicate from one point to another.
 
In this particle physics way of viewing Space and time in particle physics, people began to say there must be some particle, some boson – we called it a graviton – that is the little particle that carries the force of gravity that communicates gravity from one object to another.
 
This causes objects to realize that an object in one place has moved and the realization that this move affects the other objects to be affected differently by the one that has moved.
 
It raises all sorts of all interesting questions like how fast is gravity communicated. All these questions pointed at this little particle, this graviton that we can’t detect. This is one of the biggest annoyances in particle physics.

Fraser: Right, so we’ve moved on to the question that a 4 year-old would ask, right? Why is there gravity? [Laughter]

Pamela: And the answer if you listen to Einstein is it’s the curvature of Space and time.

Fraser: But why is there a curvature of Space and time?

Pamela: Because there is. Because mass for reasons that we can’t really explain causes the space around it to essentially grow hills and valleys that we can’t see except in the motions of objects.

Fraser: But WHY?

Pamela: BECAUSE [Laughter] this is the way our Universe is ….

Fraser: [Laughter] The point you were saying is that the thought was maybe there are particles communicating back and forth somehow. And that’s the attraction, right, is our defining the curvature of Space and we have these gravitons.

Pamela: That’s the crazy thing though, once you invoke the gravitons you no longer need to invoke the curvature of Space. We now have two views.

Fraser: Right, the little rubber bands going almost going back and forth.

Pamela: Yeah and the crazy thing about this graviton notion is first of all it is a particle that has no mass because it moves at the speed of light as near as we can tell. There are gravitons flying through us all the time.
 
If we built a detector the size of Jupiter and planted it next to something like a neutron star we’d have to wait years before maybe one graviton caused something to happen in the detector. We couldn’t tell the difference between that event and what neutrinos cause.
 
Neutrinos really don’t interact with anything either so we can’t ever really detect gravitons, except maybe through radiation. This is one of the cool things about particle physics – particles are little blobs of stuff but they’re also waves.
 
We talked about the wave particle duality in a past episode. When we look out at things like pairs of neutron stars orbiting one another we see their orbits changing over time.
 
This is gravitational radiation at a certain level carrying energy away. This is gravity waves, something that LIGO and LISA are hoping to be able to detect. We are still working to get there.

Fraser: Okay so if the particle theory is right, if there are these gravitons then you have this gravitational radiation that would be given off. It should in some way be detected through some mechanism, right?

Pamela: Yeah through gravity waves.

Fraser: Right and that’s where we get the whole thing about gravity waves which I think we’ve done a show on that as well. So that’s the one camp and I guess would there be a way that you could detect these gravitons in a particle accelerator?

Pamela: No.

Fraser: No. Not at all? No chance?

Pamela: No.

Fraser: Not even theoretically? [Laughter] Okay, fine! I won’t go with that line of questioning anymore. Then the competing thought is that it’s just purely geometry. That is the way you might as well ask why are there triangles.

Pamela: The problem is that we know that our understanding of particle physics is incomplete and we know that the geometric understanding of gravity is incomplete because we can’t describe the insides of Black Holes without math breaking. We can’t describe the earliest moments of the Universe without math breaking.
 
Having gone from basically philosophical understandings of why things fall to mathematical descriptions of how things accelerate down inclines to Kepler’s equations describing planetary motion to Newton’s formulation of the Laws of Physics – or at least the Laws of Kinematics and Gravity – to Einstein’s formulations of Relativity, we’ve been building and building a more comprehensive view of gravity. But we’re still not complete.
 
We know that there still needs to be some way to unite Quantum Mechanics and gravity and actually be able to write down equations that describe the centers of Black Holes, to describe the earliest moments of the Universe.
 
We’re not there yet. There needs to be a new brilliant person born into the Universe, or at least born onto the planet Earth. Someone on another planet might already have figured this all out.

Fraser: Now how fast does gravity move? I know that Einstein made some predictions.

Pamela: The belief – and there is some evidence for this – is that gravity propagates at the speed of light. That if you suddenly blink the Sun into some other part of Space using a transporter beam technology that will never exist, the Earth would merrily continue happily orbiting as if nothing had happened for 8 minutes.
 
Then at the end of that time, we would cease to receive light and we would start moving in a straight line instead of on the orbit that we’re presently in because the Sun’s light would stop hitting us and the Sun’s gravitons would stop communicating with us that we should bend.

Fraser: What is the mechanism that they’re trying to test this out? I guess gravity waves is one?

Pamela: Gravity waves are one. A neat experiment that didn’t work – at least the theorists are saying the interpretation is wrong – was trying to look at how does light bend around objects?
 
And if that object that it’s bending around happens to be moving can we separate out the object’s motion and the rate at which light bends around it and learn anything meaningful?
 
There is a set of observations done in I believe 2002 where they looked at how Quasar light bent around Jupiter as Jupiter moved between a series of Quasars. The interpretations were messy.
 
The observations didn’t have high enough accuracy. People are trying to find new and interesting experimental ways and like you said, we’re looking for gravity waves.

Fraser: So the hope is that as a heavy object moves in front of some distant bright object you’ll get the light beam tweaked, not instantaneously but at the speed at which the gravity is propagating out from the planet itself.

Pamela: Yeah.

Fraser: Okay, now I remember reading somewhere that gravity even though we think it is really strong, it’s actually kind of weak isn’t it?

Pamela: It is over large distances the force that tends to have the most affect on the Universe. On small scales, electrons and protons do not care about the gravitational pull of the one on the other.
 
All they care about is the electrical force. On small scales with small masses it’s extremely weak and the other three forces all dominate on the smallest scales.

Fraser: Sure, you could pick up an object from a table – pick up a coin from a table – and the nuclear force holding the atoms in your hand together vastly overpower the meager force of the entire Earth pulling on that coin on the table and just your fingers can overcome that just the force holding your fingers together.
 
Stick a fridge magnet on the fridge and bang you’ve got that little magnet completely overpowering the force of the Earth. It’s not until you get neutron stars in Black Holes where those forces are gone.

Pamela: An interesting thought experiment that basically came out of one of my classmate’s mathematical errors when I was in graduate school was to just sort out what is the self-gravity of the human body?
 
If you take a human body and pull all of its atoms apart so that it’s only held together with gravity all it would take is a breath to dispel all those atoms and shatter the human form.
 
So, it’s all the chemical bonds, all the molecular bonds, all these things that are because of the strong force, the weak force, the electromagnetic force, that hold you and I together and gravity that holds us on the planet.
 
Really, it takes a lot to tear apart a chemical bond and it’s only on the largest scales where chemistry no longer really has an effect that gravity has a chance to get noticed.

Fraser: Well, I think that covers our gravity side this week. Next week we will move on to the Electromagnetic Force and then we’ll do the Strong Nuclear Force and the Weak Force and then maybe on the last episode – the fifth episode of our four-part series – [Laughter] we’ll try and pull it all together.
 
We’ll talk about the search for the grand unified theory. Pamela if you figure it out – Nobel Prize.

Pamela: You know, it’s something to aim for but I don’t think we’re quite going to make it.

Fraser: Just do your research, [Laughter] get all your show notes prepared and if the solution seems to present itself then by all means put it in the show and we’ll look forward to a Nobel Prize. [Laughter]

Transcript:

Download the transcript

Fraser Cain: Gravity is always pulling you down, but there are places in the solar system where gravity balances out. These are called Lagrange points and space agencies use them as stable places to put spacecraft. Nature is on to them and has already been using them for billions of years.
 
Before we get on to it, let’s talk about pronunciation. I said it Lagr-ahunge points. Is that okay?
 

Dr. Pamela Gay: I have heard it said Lagr-ahunge points, Lagr-ahungian points, Lug-range points and Lug-range-ian points. So you know – go with it. Say whatever your local dialect dictates is correct.
 

Fraser: They’re acceptable.
 

Pamela: They’re all acceptable.
 

Fraser: All right. Maybe someone from France can jump in and give us the most correct pronunciation.
 
So, where do these come from?
 

Pamela: The basic idea is if you have a two-body system with two giant things – where giant can be defined on small scales, such as the Moon and the Earth would qualify, the Earth and the Sun would qualify – then you throw in something small (a test particle, a frozen pea, a satellite), you can look to see how the smaller object is going to gravitationally interact with the larger object.
 

Fraser: The point being this object isn’t going to be pulling at the other two objects with its gravity. Its gravity is negligible in the situation.
 

Pamela: Yeah. It has no pull on the Earth or the Sun – no pull on the two giant objects that we’re worried about.
 
When you start to probe all the different places you can stick this test particle, there are some places that when you stick it there, it stays. In general, if you take an object and you put it on an orbit around the Sun that’s bigger than the Earth’s orbit, it’s going to go around the Sun a little bit more slowly. When you stick it on an orbit that’s inside of the Earth’s orbit from the Sun, it’s going to go around the Sun more quickly than the Earth.
 

Fraser: If you have an object, which you’ve got the Sun and the Earth, the interaction of the Earth is going to mess with it, right?
 

Pamela: That’s where the magic happens. There are a few specific points – five of them to be exact – that if you stick an object exactly in one of these five points, the combined gravitational attraction of the Earth and the Sun gang up on this object to keep it moving in lockstep with the Earth as it goes around the Sun. If you’re dealing with the Moon-Earth system, you can stick things in the five specific spots that come from the combination of the Earth and the Moon so that it sticks there, following the Moon in its orbit around the Earth in lockstep.
 

Fraser: Hold on, so you’re already said places where its stable. What if you’re not in one of those places?
 

Pamela: if you’re not in one of those places, you’re happily going to end up in some sort of orbit going around the object, but you’re not going to be synced up with anything. For instance, the space shuttle at the space station right now is zipping around the planet every 90-100 minutes. The moon, on the other hand, takes 20-some-odd days to go around the planet.
 
If I move the space shuttle and the space station its attached to, out into gradually further and further orbits, and position it in just the right orbit in just the right period of time, even though it’s not as far away from the Earth as the moon, it would still go around the Earth with the same orbital period as the moon. It’s in one of these magical Lagrangian spots where the potential and kinetic energies of the systems balance out just right to keep it there.
 

Fraser: Right. If you slowly move it out and don’t necessarily have it in a perfect circular orbit, it might get caught into some weird, gravitational dance, and get thrown out of the system or hurled into the Earth or sent into orbit around the Sun, or…
 

Pamela: Most likely it will just end up in a very elliptical orbit around the Earth.
 

Fraser: Right, get turned into very elliptical orbits. So if you have a little space rock that comes into our system, in most situations it’s going to crash into the Earth, crash into the Moon, get skewed away into an elliptical orbit or…
 

Pamela: It’s just going to be another satellite.
 

Fraser: Yeah. It’s not going to stop and pause and stick around. Let’s talk, then, about these Lagrange points. How do they work?
 

Pamela: There are five of them that are ever so creatively named: L1, L2, L3, L4 and, well, L5.
 

Fraser: And that’s Lagrange-1, etc. Right?
 

Pamela: Right. So Lagrange-1 is the point between the two masses that stays in sync with the smaller object. For instance with the Earth-Sun system, this is the point in space nearer the Earth that, if an object is plunked down in L1, it goes around the Sun in the same just about 365 day period that the Earth has. We will always have this constant line going Sun-object-Earth lined up like little soldiers.
 

Fraser: So if we take that object and put it closer to the Sun, it’s going to be travelling at a faster orbit like Venus, so it will go around the Sun faster than the Earth will.
 

Pamela: Normally.
 

Fraser: Yeah. If we move a little more toward the Earth from that point, it will still be going faster than the Earth will, but it will actually be going slower than that point. Right? If that makes any sense. You’re saying it goes in lockstep with the planet, so…
 

Pamela: Here’s a different way of looking at it that’s a little bit weird. If I take an object and put it the exact same distance from the Sun as L1, but I plunk it down so the Earth, Sun and this object form a right angle from above, that object is going to start going around the Sun with its own period that is way shorter than one Earth year.
 

Fraser: Right.
 

Pamela: It’s just going to be heading around following Kepler’s laws.
 

Fraser: Right.
 

Pamela: Now if I take that object and take it at that specific distance from the Sun at just the right moment so that you have Earth, Sun and this object in a straight line with the object between the Earth and the Sun, and then I give it just the right amount of momentum, it’s going to travel around the Sun with the exact same orbital period as the Earth.
 

Fraser: Right. I’m going to make a guess here, but the point is the Earth is tugging on it and providing just that extra little bit of oomph to keep it going around at that speed.
 

Pamela: The Earth is giving it that extra pull. Well, not so much an oomph as it’s combating the Sun’s pull. It’s because of the Sun’s mass that the object would normally be zipping around so quickly. If you have the Earth pulling in the exact opposite direction, in a way philosophically, it’s like you removed a chunk of the Sun. if you make the Sun smaller you can orbit it more slowly.
 
By having the Earth there, pulling away with its own gravitational pull, it slows down the velocity that’s needed to stay in a nice stable orbit around the Sun.
 

Fraser: I’ve got an analogy. If you’re diving and you’re going to wear a weight belt to keep yourself perfectly stable, then if you want to go back up you could attach a balloon behind you that would start pulling you back up. You could balance it out with weights and balloons, with the Sun being the weights and the balloons being the Earth. The right spot is your Lagrange point. 1
 

Pamela: Just like with the weights and the balloons, you have to get it exactly right or you’re either constantly floating or constantly sinking. With the Lagrange points, especially with the first three, you have to get it exactly right, or you’re going to go flying out of it. These aren’t stable locations to be. The spaceships we stick there have to have their own engines and they’re constantly making their own corrections to stay in these places.
 

Fraser: Okay, so these spots, although you can keep going at that same orbital speed, they’re not stable. It’s almost like you’re at the top of the point of a needle, and you can fall any direction and have to fall out of that Lagrange point. The only way to stay there is to keep using your rockets.
 

Pamela: Mathematically they’re what we call saddle-points. In certain directions, you’re going to fall right back down to the Lagrange space. If you’re taking a marble and trying to balance a marble on a western saddle, if you move it toward the head or butt of the horse, the marble will roll right back to the centre of the horse’s back. If you bump the marble left or right, it’s fallen off the horse. I know people (including myself) who have had the same experience of falling off the horse.
 
These are semi-stable positions. The spaceships we stick there have engines that make corrections to stay put. At the same time, it’s so convenient to have something that isn’t in the Earth’s orbit, and is following us around the Sun. it makes communications easier. It’s worth the expenditure of energy.
 

Fraser: Right, if you wanted to put a spacecraft there and didn’t have the help of the Earth’s gravity, you’d have to fire your rockets non-stop, using tremendous amounts of fuel. Even though you’ve got to do minor corrections to stay at that sweet spot, it beats having to fire your rockets non-stop o stay in that kind of position.
 

Pamela: So with the L1 spot, which is between the Sun and the Earth, that’s someplace we stick things that are observing the Sun for us. What’s cool is they’re just enough closer to the Sun that in a lot of cases, when there’s a particle spray – a bunch of electrons headed our way from the Sun – they might hit SOHO that’s hanging out at L1 a little bit before they hit Earth, about an hour earlier. That gives us extra time to protect our astronauts and put satellites into safety mode, because SOHO can send us radio signals at the speed of light that these electrons are coming toward us at less than the speed of light.
 

Fraser: Right. Okay, so that’s L1. What’s L2?
 

Pamela: If you have a position between the Earth and the Sun, there’s also a point that’s on the same line but it’s beyond the Earth. So you go Sun-Earth-object, and that we call L2 (ever so creatively).
 
Normally if you stick an object on an orbital path bigger than the Earth’s orbit, it will orbit a little bit slower. Since you have the added pull of the Earth, it’s like making the Sun a little bit bigger, so an object can orbit faster and still be stable at that greater distance. It’s not entirely stable: just like L1, it’s saddle shaped and you can fall off the Lagrange point. It’s still a great place to stick things that have to make corrections because it makes the communications easy.
 
For instance, the Herschel satellite, the Planck satellite, the James Webb Space Telescope are all candidates for the Lagrange-2 point. WMAP, the microwave anisotropy probe that has given us such wonderful information about the cosmic microwave background is hanging out at the Lagrange-2 point.
 
This is a good place to put things that is protected a little bit from the Sun’s light, by the Earth hanging out there. It’s in a nice safe place beyond the Earth, following us around an orbit, and because it’s not orbiting us, instead orbiting the Sun, all the random junk that orbits the Earth is not in any danger of hitting these things in the Lagrange points. The radiation doesn’t get there. It’s a nice safe place to stick things that work in the infrared and radio that need it a little bit quieter and a little bit darker.
 

Fraser: So you wouldn’t necessarily want to have one of those satellites orbiting the Earth, because of our radio static.
 

Pamela: Our heat.
 

Fraser: Our heat. Right. That would actually cause them some problems. So if you keep them away from the Earth, they’ll be cold, and will have fewer radio waves blasting them. They’ll have a chance to observe better the state of what the universe really is. At the same time, you want to put them some place where you’re not going to have them firing their engines non-stop. You also don’t want them somewhere you can’t communicate with them.
 
Yeah, I can imagine if you pushed one of those telescopes out to a larger orbit than the Earth, it’ll slip behind us in orbit and there will be times like when we’re trying to communicate with the rovers on Mars, right? They’re on the other side of the Sun and there’s no way to communicate with the rovers. If we put them in the L2 point, then it’s there in the exact same spot in the sky – which probably makes communication a lot simpler, less power on the spacecraft than the kind of thing the rovers need to communicate with (though they relay stuff through satellites).
 
So I can see it makes a lot of sense. Okay. What’s the next point?
 

Pamela: Then there’s L3, and we don’t have anything hanging out there. L3 is the one that’s opposite us, so that it goes Earth-Sun-object. If you can imagine an object that has an orbit on the exact opposite side of the Sun from us where it’s getting pulled on by both the Sun’s gravity and the Earth’s gravity. Even though it’s not the same distance as the Earth from the Sun, it’s orbiting with the same period, constantly staying in lockstep with us, always out of sight.
 

Fraser: So if I imagine this right, you’ve got the Sun and the Earth and I guess the combined gravitational force is pulling on this object. That feels to me like it would fall into the Sun.
 

Pamela: Here we’re talking about an object that has an orbit that’s again, a snert bigger than the Earth’s orbit. It’s trying to head off in a line to get away from the Sun, but it’s the combined gravity of the Earth and Sun that’s keeping it on its circular orbit, chewing around in lockstep with the Earth. This is very similar to L2, but it’s beyond the Sun from us.
 

Fraser: So if you were to look at the line from above it would be like this object will be almost the same distance from the Sun as the Earth…
 

Pamela: Almost.
 

Fraser: Hard to calculate or see, but a little bit more. Instead of just going into a larger orbit, the way it should if it’s further away from the Sun, the Earth is almost increasing the mass of the Sun and keeping it at that exact same orbit.
 
Okay. Is it stable?
 

Pamela: Again, it’s a saddle point. The objects are going to want to fall out of that spot. If it can balance just right, or has engines to keep it balanced, it will stay there.
 

Fraser: There are no spacecraft planned for that, are there?
 

Pamela: No, because the communications isn’t possible.
 

Fraser: But I can imagine it would be great. If you ever had SOHO, you could put another SOHO on the other side of the Sun and observe it at all times.
 

Pamela: The trick is you start needing to have things at the right angles between the Earth, Sun and the object so that you can relay the communications around the Sun, just like we have satellites that allow us to relay communications around the planet Earth. We can’t talk directly to a satellite that’s through the planet, on the opposite side of the Earth in its orbit. Instead, satellites can relay communications from one satellite to the next to get from Australia to Washington DC.
 

Fraser: Right, so if we had other satellites going around Venus or in some of the other Lagrange points, you could actually get this communication. So you could always observe the front and backside of the Sun at the same time.
 

Pamela: Then just relay the information all the way around and put it together in the lab later.
 

Fraser: There might be uses for those. Would they be useful going around the Moon, in the Earth-Moon system?
 

Pamela: This is where you start to get into space elevators and other crazy stuff. Let’s talk about L4 and L5 to get them out of the way first.
 

Fraser: Sure, yeah.
 

Pamela: There are two more Lagrange points left, just two. These are the most stable. They are points that lag behind the Earth in its orbit and ahead of the Earth, such that if you drew an angle from the Earth to the Sun to either L4 or L5, both of those angles are 60-degree angles.
 
There are these hills that it’s capable to stand on top of and just hang out there and be gravitationally balanced.
 

Fraser: So it’s the combination of the gravity from the planet pulling you forward, and you’re still going around the star, keeping you in that orbit. If you fall too far back, the gravity of the planet pulls you back in. this is the opposite of that saddle. It’s very stable – it requires energy to get out of this orbit.
 

Pamela: The objects are hanging out here. They’re getting tugged forward by the Earth, or pulled back from the Earth, because their natural inclination is going to have different periods than what they are. It’s really neat that if you have a map of your potential of hanging out in any particular point, these are actually at the tops of hills. They’re fairly flat tops of hills. Once you’re up on top, you have to take effort to fall off. What’s cool is you can actually end up with things inside these larger L4 and L5 points on little tiny circular orbits, where they’re going around within the L4 or L5 point and also going around the Sun. that’s just kind of neat.
 

Fraser: So it’s like a volcano. You’ve got a mountain where it’s quite hard to get into that point, but once you’re at the top, there’s actually a crater inside that’s easy to roll down into.
 

Pamela: Sort of like that, yeah.
 

Fraser: Not that there’s actually volcanoes in space, but that’s the way the gravity works.
 
[laughter]
 
So if we were to put a spacecraft into one of these L4 or L5 points, same deal – they’d just sit there, no energy required, right?
 

Pamela: What’s cool is there are asteroids hanging out in the L4 and L5 points of Jupiter. We call these the Trojan asteroids. It looks like Neptune also has its own Neptunian version of Trojan asteroids that may even be more populated than Jupiter’s. Mars is tugging on asteroids as well, holding them locked in its Trojan points. These are places where the solar system likes to store its rocks.
 

Fraser: We don’t have any going around the Earth?
 

Pamela: Not as much as these bigger things like Jupiter and Neptune.
 

Fraser: I wonder, if you could fly some asteroid observing telescope out to the Earth L4 Lagrange point and place it there, would it see rocks and debris and stuff in a cloud?
 

Pamela: I’m sure the density of rocks and pebbles and pea-sized bits of gravel in the Earth’s Lagrange points is probably higher than they are elsewhere in the solar system. These are just good places to store things.
 

Fraser: If you were sitting on Jupiter’s orbit, maybe standing still on Jupiter’s orbit while it and its Trojans go around, you’d be standing there and a whole pile of asteroids would go past you, then Jupiter, then a whole pile more asteroids.
 

Pamela: Oh yeah. That’s the really cool thing. If you look at a plot of where rocks are in the solar system, if you look at a plot of where all the asteroids are located, there are just piles of them in Lagrange points for Jupiter, Saturn and Neptune. That’s just neat to look at.
 

Fraser: We talked a bit about spacecraft we might put in some of those Lagrange points. I’ve heard ideas of putting spacecraft into the L4 and L5 points as well – space colonies, space stations. It’s so stable it doesn’t require energy once you put it in there.
 

Pamela: That’s one of the places they have at various points talked about, with the Earth-Moon system, sticking space stations.
 
What’s also cool is with the not particularly stable, but we have engines to fix it L1 and L2 points in the Earth-Moon system, you can start to think about building space elevators with regard to the Moon.
 
The moon is facing the Earth the exact same way all the time. It’s going around the Earth at the same rate that it’s rotating about its axis. So if you have something in the Earth-Moon system’s L1 or L2 point, it’s essentially in geostationary orbit around the Moon. It maintains the same orientation with the same plot of land on the surface of the Moon all the time.
 
It’s not the same way with the Earth. The Earth rotates about its axis fairly quickly. There are specific geostationary orbits that we stick communications satellites in. With the Moon, you can use the L1 and L2 points. So you can conceive of potentially some day sticking some sort of space station in geosynchronous orbit above some point on the equator where there’s land and building a carbon nanotube space elevator tether and dropping it down to the surface of the Earth.
 
You could have an elevator to get to geosynchronous orbit (which is pretty high up). Then you fly your little rocket from that craft to something that is in the L1 orbit between the Earth and the Moon and you take a different elevator down to the surface of the Moon. Hang around, walk to the exact opposite side (you’d probably actually want a vehicle of some sort) and then take an elevator up to the L2 point which is pointed away from the Earth-Moon system and could be pointed away from or toward the Sun, or at right angles. You could use that as a jumping off point to escape the Earth-Moon gravitational system.
 

Fraser: that would be awesome. Like heaven! How cool would that be?
 

Pamela: It’s a brave new sci-fi universe.
 

Fraser: Let’s get on that, people!
 
[laughter]
 

Pamela: It’s a bit expensive.
 

Fraser: I want my space travel!
 
[laughter]
 
I actually did an article on that space elevator concept. The advantage is since you attach the elevator to the surface of the Moon, you don’t have the problem with the instability of the L1 point, because it’s tied to the ground. Just like a balloon really wants to float away, you’d be able to tie your ribbon down to the Moon and even though it’d be trying to get out of that orbit, it would be continuously held there.
 

Pamela: The only thing that’s a bit scary, and anyone who’s read Kim Stanley Robinson’s Red Mars series has read about this, is what if the cable breaks?
 

Fraser: It would come toward the Earth.
 

Pamela: Yeah, and you can end up with a ribbon of destruction wrapping itself around the planet. That’s a rather bad thing. So yeah, there are all sorts of safety things to be figured out. It’s still a cool plot point and a cool thing to dream about and imagine. The future has so many possibilities. It’s fascinating to think about what’s possible thanks to these neat gravitational holes in space.
 

Fraser: So now hopefully, if you hear someone bring up Lagrange points, or if you read it in an article, you’ll know what they’re talking about. Thanks Pamela!
 

Transcript: Questions Show #8

Download the transcript

Fraser Cain: We’ve been so crazy following our own whims through the universe that we’ve neglected your questions. That ends today. It’s time to dig deep into our overflowing email box to retrieve the puzzling questions our listeners have sent in.
 
Let’s start with what I think is our best question ever.
 
[laughter]
 
This is it, this is the greatest question. Justin Craig sent in an awesome email. He says, “I was wondering, if you had enough anti-matter and you put it into a black hole with an equal mass, would the black hole disappear or just become twice as heavy?�
 
Now, before we go into the actual answer of question, let’s give the listeners background on anti-matter. I don’t think we’ve done a show on anti-matter, so what is it?

Dr. Pamela Gay: Anti-matter is basically the “Spock has a beard� universe of matter if you’ve watched old generation Star Trek. An electron of antimatter has the opposite charge. It has all the opposite physical characteristics that a regular electron has. So you have an electron and a positron, take one and turn it inside out in every way you can (except for the mass – you can never have negative mass, it’s always a positive quality), and it’s exactly the opposite. Opposites often annihilate one another.

Fraser: This isn’t just some crazy, calculated theory. This is real stuff – you can calculate it in the lab, you can smash it together, it annihilates and produces a gigantic amount of energy. This is real stuff.

Pamela: Yeah, we’ve produced positrons – I think they’ve even put together anti-matter hydrogen and helium anti-atoms in various laboratories. You’re just very, very careful to suspend them away from everything else while you’re working with them. But we can create these things.

Fraser: So this isn’t some theoretical concept. Astronomers see the presence of antimatter out in the universe, being produced naturally. In fact, it was recently announced there’s a cloud of antimatter in the Milky Way.

Pamela: There’s a bunch of natural processes that it’s just part of how energy settles out when it’s becoming matter. If you take energy and you say, “okay, let’s change it into matter� you’re going to get a regular matter particle and an antimatter particle. Everything is created in the yin and yang, in terms of you have to have a positive charge and a negative charge. All of these things have to balance out in these energy goes into matter reactions. In some cases it can actually create clouds of antimatter.
 
There’s a cloud here in the Milky Way that we detect because of the very specific gamma ray light it gives off, that has a colour that you pretty much only get when you have these matter/antimatter reactions. We think this is perhaps coming from low-mass x-ray binaries that are creating this cloud of antimatter.

Fraser: All right. We know there’s antimatter, but just creating clouds which are annihilating instantaneously. We’re not actually clumping together gigantic quantities – enough to say, create a black hole. But let’s say we could. We’ve pulled it all together and fashioned it into a ball of antimatter with exactly the same mass as our target black hole. Then we smash them together.

Pamela: Here’s where I said it’s really important that mass is always a positive quantity. If you take a pile of matter and a pile of antimatter, they’re both going to have the same gravitational effects on things, they’re both going to have the same style event horizons… they’re going to have the same everything.
 
The thing is, with a black hole, you can’t tell if it’s matter or antimatter.

Fraser: Whoa.

Pamela: Yeah.

Fraser: Right, of course. So an antimatter black hole would, in all cases, feel identical to a regular black hole, if you’re trying to orbit it or whatever.

Pamela: If you basically went around with some sort of antimatter vacuum cleaner and collected antimatter into a bigger and bigger and bigger pile until the pile had enough mass (regular mass with antimatter characteristics), that it condensed down to a black hole… it’s a black hole. When you take an antimatter black hole and a matter black hole and throw them together… we don’t know what’s going on within the event horizon. From the outside perspective, you just made one really large black hole. Which is kind of cool.

Fraser: Hold on, let’s break this down a little bit. Say we have our antimatter black hole and we’re streaming planets and asteroids at it, they’re just disappearing into the antimatter black hole. Now, there would’ve been an explosion going on as these asteroids are striking the antimatter, right?

Pamela: The problem is you’re starting from the assumption the matter inside a black hole is normal. It’s not – at least, we can’t think of any way that it’s normal. So the whole idea that you have electrons goes away. The whole idea that you have protons goes away.
 
What you have is some surreal quark soup that all the different bits and pieces that make up both matter and antimatter are slammed together and forced into these really small volumes. Things lose their identity in the process.

Fraser: We’ll get that question in a second – we’ve actually got another question on that identity and information. I guess my question – sorry to not let go here – let’s imagine you had your antimatter black hole and your regular matter black hole, wouldn’t your antimatter black hole be the exact same configuration as the regular black hole, just the antimatter version of that/
 
Say it’s some kind of soup of particles which no longer look like protons/electrons/whatever. Wouldn’t they just be anti-versions of whatever’s in the black hole, and wouldn’t that still create the explosion?

Pamela: How do we know, because it’s in the event horizon, that these particles are able to hold on to that level of identity? How do we know they haven’t turned into pure energy as they cram themselves in there?

Fraser: Let’s say we do know. Let’s say they do remain as a mere version of the particles that are in a black hole. What happens then?

Pamela: Well, it’s just energy being released, but that energy can’t get out because it’s a black hole.

Fraser: Well that’s the question isn’t it – the energy can’t get out because it’s a black hole which would stop even energy. So obviously you’re not going to have an explosion of chunks of things because they would just be sucked down. You’re not going to have radiation because it’s going to get sucked down. You’re not going to get sound…. Anything. There may very well be an explosion, but you wouldn’t know it happened. Is that right?

Pamela: Exactly. Basically, what goes in stays in and we can’t find out anything beyond that. Since the antimatter systems have positive mass, you just have a bigger black hole.

Fraser: Right. Wow.
 
All right. I think that’s it – I guess, that’s the question at the heart of it. The hope was maybe the two would cancel each other out and you’d be able to break past black hole-ness, right, and the whole thing would explode and turn into a release of energy. Even energy can’t escape this black hole, so even if there is a release of energy, no one’s the wiser.

Pamela: Exactly.

Fraser: Awesome question. Best question ever.
 
[laughter]
 
Let’s get on to some other best questions ever. Let’s go with that – continuing on the information.
 
We had a question from Maureen Egan, and she wants to know, “in terms of information not being able to escape the gravitational pull of a black hole, what exactly is information? When I imagine information I think of data like that stored on a floppy disk or CD.�
 
I think astronomers do use that term quite loosely – all the information is lost, so who knows what happens to it. But what is information?

Pamela: I’m not sure so much that we use the phrase loosely as we just throw it around a lot without ever telling anyone what it means.

Fraser: Oh, fine – yeah.

Pamela: Which is a little bit more evil on our part.

Fraser: Yeah, no – I just throw around, “information’s gone – moving on�
 
[laughter]
 
“Stop, what does it mean?� So really – what does it mean, information loss?

Pamela: It’s an idea that came out of quantum mechanics. It’s this whole idea that particles have varied states in them. If you take an atom – let’s talk about helium, which is nice and simple. In a helium atom, you can have two different electrons. One is going to have spin-up and the other will have spin-down if they’re both in their lowest energy state. This is something that comes from the poly-exclusion principle, which says you can’t have two electrons with the same spin in the same orbital.
 
The fact that one is spin-up is information. The different states particles take on, or the different wave functions, all of this is different types of information. It’s the quantum states that are tied up in particles that people try and figure out how to take advantage of in building the next generation of hard drives where we store information in the spins of electrons.
 
How do we figure out how to tap into this so that we can build atoms that store the genetic code of the human genome, or something crazy like that. I don’t think you can actually do that one.

Fraser: Maybe we could do an analogy in star trek, like where you hop in a transporter and you’re going to be teleported from where you are to the moon down below. You want to make sure that the teleporter can rebuild you, atom by atom, and for it to be able to do that it’s going to be able to put an atom here with this quantum state, an atom there with that quantum state, etc. It’s got to get it exactly right or you won’t be you anymore. You’ll be somebody else, or even just a mess.

Pamela: All of this can include information such as what the polarization of a photon, what is the orientation of the waving of the electric and magnetic fields of that photon as it passes through space.

Fraser: So there’s any number of ways you could measure an atom or a photon or a particle or anything and that’s the information that is thought to be destroyed when it goes into a black hole.

Pamela: It’s the most basic way of putting this is what are the quantum states of the particles – that’s the information the particles carry.

Fraser: So the thinking is that if you could somehow pull that stuff back out of the black hole, there would be no way to re-create that information. No way to ever know what its quantum state was.

Pamela: Yeah.

Fraser: Why is that bad?

Pamela: Well, we like to think that no information is ever lost. Ever particle in some way, holds its entire past inside of it. It couldn’t exist if a whole series of different things hadn’t existed. You take energy and that energy has to split into a positive and negative charge, different spins that are conserved… you have all these different things that have to get conserved in the creation of matter and reactions and there are very specific processes that are the only allowed atomic processes, as particles decay from one to another through time.
 
If this information could get lost, it’s sort of like erasing the history of the particle, which is kind of sad and also implies that there’s information about our universe that gets lost forever.

Fraser: Right, but astronomers aren’t boo-hooing about lost information. This information loss breaks something, right?

Pamela: Well, one of the tenets we start with is no information can ever be lost or destroyed. If black holes can lose or destroy information, there’s one of our basic tenets gone, and that makes people uncomfortable.

Fraser: Okay, I think we could talk about this all day. Hopefully that gives you the information you were looking for, Maureen, and we’ll come back around and talk about information in black holes… that’s a whole show, I’m sure.

Pamela: Yeah. The short answer is, as near as we can tell, black holes don’t eat information – it has ways of escaping. But that’s for another entire episode.

Fraser: Right, right. Okay. But when they’re talking about information, that’s what they’re talking about – the quantum state of the stuff that gets consumed.
 
Let’s move on and go to our next question. This is from Mark Maultby. “If gravity is the force of interaction between objects, what is the smallest object that could noticeably be said to have gravitational attraction?�
 
I just want to set some scale here. If I have the Earth, with the Sun… Here we are on the Earth, feeling its gravity. If I go across the universe, to the other side of the universe, I’m still feeling the effect of gravity from the Sun, right?

Pamela: Oh yeah.

Fraser: Now, not much, obviously.

Pamela: Not noticeably.

Fraser: It’s so miniscule you can’t even have numbers to describe it, but it is there. Every piece of matter in the whole universe is interacting gravitationally with every other piece of matter in the whole universe. That’s true?

Pamela: That is exactly true.

Fraser: Okay. All right, and then that doesn’t matter for any size – for a planet, a moon, a proton, an electron, a neutrino… anything, there’s still a gravitational force that’s being done across the universe. I guess the question is, is there some point where that doesn’t happen anymore?

Pamela: No. It’s either you have mass – and if you have mass, then you affect things with gravity. Or you have no mass, in which case you can fly across the universe at the speed of light.

Fraser: Is there a minimum amount of mass you can have/

Pamela: Nope.

Fraser: But, we had this conversation just a couple of weeks ago about the Higgs-boson. I know there’s the concept of gravitons. Is there some number where, if you’re smaller than the Higgs-boson, then you won’t have mass? Like, you need to have one Higgs-boson to have mass – I’m speaking gibberish, right?

Pamela: That’s one of the crazy things. Higgs-bosons have a fair amount of mass.

Fraser: Theoretically.

Pamela: Or at least, they have a fair amount of energy (and energy and mass are kind of interchangeable, which makes the way we talk kind of confusing). The real question comes down to what is the least massive particle that we know about? That’s probably quarks. Three quarks combine to make a proton.
 
I think the real question is what the particle is with the smallest mass out there. Here you have to start remembering there’s quarks, and they combine to create protons and basically have mass (in a sort of weird kind of way). Electrons have mass, neutrinos have mass. Then there’s this stuff called dark matter that we don’t know what the heck it is. It has mass. It gravitationally effects things.
 
I’m not sure we know, yet, at this point in time, exactly what the smallest particle out there is, because we’re still discovering particles. We’re still trying to figure out what this weird stuff called dark matter is. But it’s basically, when you start getting down to these… this is a single lepton, a single boson, a quark… these individual units have slightly different masses, but these are the smallest things (smaller than atoms), that are capable of gravitationally affecting other things in the cosmos.

Fraser: But that kind of feels like you’re not quite answering the question.
 
[laughter]
 
You’re kind of saying that these are the smallest particles that we know about – that we know exist for sure – and we know that those particles have mass, and therefore they can gravitationally attract. If you had one quark on one side of the universe and another on the other side of the universe, if they weren’t being expanded away from each other, they would eventually come together, over a long time.
 
But the question is, is there some theoretical limit where you just can’t have any less mass?

Pamela: When defining the smallest possible things, we often say, “there’s the Planck unit of time� (the smallest discernable unit of time), or there’s the Planck length… You’d think there’d also be a Planck mass, which would be a limit to how small mass could get. But there’s not.
 
As far as we know, there may not be a limit to how small something can get in terms of mass, but we’re still figuring out the particle world. We still haven’t found the Higgs-boson (if it exists). We still haven’t found the graviton (if it exists). There’s this whole realm (potentially) of different particles that don’t interact via the electromagnetic force like electrons and protons do, that are making up dark matter. For all we know, the least massive particle out there is also the most common particle out there and happens to be whatever it is that makes up dark matter.
 
We’re still learning. Particle physics, the standard model, these are things we’re still working to define. As far as we know, no – there is no mandated-by-the-cosmos boundary on how small a mass we can get. We’re still exploring.

Fraser: I guess the question will maybe help to be answered by upcoming work with the Large Hadron Collider.

Pamela: Yes.

Fraser: We don’t really know. That was a good question too.
 
[laughter]

Pamela: These are the ones that stump me.

Fraser: I know, I know. Let’s move on. Something I think is a little simpler – this comes from Sabre Rosewood and the question is: “since the tides on Earth are part of what causes our moon to slowly move away, what will happen once the oceans are gone? Will the Moon stop moving away from the Earth?�
 
We talked about this in our show “Where Does the Moon Come From?� and discussed that – the Moon is slowly moving away from the Earth. What’s the cause of that?

Pamela: It boils down to conservation of angular momentum. The Earth isn’t a perfect sphere: it has mountains, it deforms itself due to the gravitational pull of the Moon. As the planet rotates, it bulges out so that part of it bulges toward the Moon and part of it bulges in the opposite direction because the gravity is not so strong over there.
 
This deformity basically gives the Moon a gravitational handle to hold on to our planet and say, “no – don’t rotate past me, keep the bulge pointed this direction!� The rotation of the Earth is constantly trying to carry the bulge past the Moon. Gravity grabs that bulge and pulls it back. This pulling back on the bulge that’s trying to rotate past the Moon is slowly, slowly, slowly, slowing the rotation of the planet.

Fraser: You’re talking about a bulge that’s coming from mountains or one side of the Earth is a little more bulged than the rest of it. Oceans move huge distances – more than the mountains ever move. There’s a gigantic amount of ocean on the planet, so does that play a significant role in this?

Pamela: It plays a significant role, but it’s not the only role. So, 50 million years from now, when our oceans start to evaporate away, we’re still going to have these tidal effects. We’re still going to have this planetary flexing that prevents us from becoming a perfect sphere ever. This planetary flexing is going to continue to slow the rotation of the planet until eventually we’re completely locked so the same face of our world is always facing the same face of our moon.

Fraser: And the moon will stop moving away.

Pamela: It will stop moving away.

Fraser: Right, so the oceans are part of the bulge on the Earth, but they’re not the whole thing. Eventually, even when the oceans boil away, the Earth and the moon will still go through this dance until they figure it out – until the Earth and moon are facing the same side toward each other forever and always. Which I think would be longer than the lifetime of the Sun, right?

Pamela: Yeah, that’s what we think right now at least.

Fraser: It’ll be a red giant before it happens.
 
Okay, cool question. Let’s move on. Paul Barnett asks “Since the universe is expanding and we believe that matter cannot be created or destroyed but only changed from one form to another, I’m curious to know where the new matter comes from to occupy the new space that’s created. Is there new matter being spontaneously created?â€?
 
Now, let me try and rephrase the question, because I think he made a couple of mistakes there. We talk about the universe expanding, the expansion of the universe, both from the big bang but also from the additional dark energy that’s helping to push the universe apart. We’re getting more space in between the galaxies and galaxy clusters and interstellar space. But we’re not necessarily getting any space in between the galaxies because they’re held together.
 
I guess the question is, let’s look way out into the most unpopulated part of the universe where space is expanding apart and we can measure the density of how many atoms per cubic kilometre there are out there. As the space is expanding from dark energy, is there any more matter coming into existence?

Pamela: No, that’s the cool thing. The universe is basically diluting itself over time.

Fraser: So it’s like you’re pouring water into something that was quite thick, and it’s just making it more and more dilute – more and more thinned out.

Pamela: Or, the way I like to think about it, if you imagine blowing up a balloon, the balloon has very thick walls when it’s small, but the more and more you blow it up, the thinner those walls get, the fewer atoms there are per square centimetre of area on the surface of that balloon.

Fraser: Until it pops.

Pamela: Until it pops.

Fraser: Our universe isn’t going to pop, is it?

Pamela: No.

Fraser: Okay.

Pamela: But it’s going to get pretty empty.

Fraser: Right, and that’s it – there could be some point in the far, far future where everywhere you look, there’s no atoms around. Right now, I forget – did you mention how dense space is?

Pamela: It’s on the order of nothing per cubic meter?

Fraser: Right, okay. The occasional particle per cubic meter, but you could eventually get to the point where there’s one particle per light year.

Pamela: What’s weird though is this is true of atoms of normal matter. There’s this thing called dark energy, and near as we can tell, dark energy is constant at all times. When we look at how much energy there is per cubic meter of space, it works out to a few protons worth of energy at all points in time, even though the total volume of the universe has increased.
 
That means the amount of energy, the amount of dark energy in the entire universe, is somehow increasing as the universe gets larger, because its staying constant as a function of volume. This gets confusing.

Fraser: I’ve got a zinger for you now, then. We always talk about the fact that matter and energy are interchangeable. So, is dark energy interchangeable with matter? Could you freeze it into matter?

Pamela: As far as we know, no. Dark energy is this weird enigma, currently. We don’t know what causes it. As near as any theorist that I can understand has gotten, dark energy is basically a field of energy that permeates all of space and time. If you can imagine this mesh of energy that is everywhere, all at once, and not getting all metaphysical on me… if you can imagine this lowest possible energy state (that isn’t zero) it permeates everywhere. One of the fears is something will come along and trigger that wave, that field that permeates everywhere to crash down to zero and no one knows what will happen.

Fraser: Now you’re freaking people out here.
 
[laughter]

Pamela: Theorists do scary things with their mathematics sometimes. Like I said, we don’t really understand it right now. So, give us a few years.

Fraser: Okay. To summarize then, with the expansion of the big bang and the addition of dark energy, the universe is growing but the amount of matter in the universe isn’t changing, so it’s really just getting diluted. So, back to the question where’s the matter coming from, it’s not coming from anywhere – there’s no additional matter. All the matter in the entire universe was created in the big bang, and that’s all we’ve got.

Pamela: That’s all we’ve got.

Fraser: All right. Speaking of all we’ve got, there’s one more question. This is a good one too, in fact this is a question I was going to ask you about and I never got around to it.
 
This one comes from the forum, the Bad Astronomy & Universe Today forum. “I can’t wrap my head around the physics of gravity assist. Why does travel in the same direction of an object’s orbit speed something up, while travel in the opposite direction slows it down? I keep thinking the approach push and depart pull would cancel each other out either way and not change the speed at all.�
 
This is great – I’ve thought about it too. You’ve got a spaceship going toward Jupiter and it’s going to get a gravitational assist to pick up velocity and go much faster. As it approaches Jupiter, Jupiter is speeding it up. I get that – it’s velocity might be changing as it’s falling into Jupiter’s gravity well. As it does its fly past, and starts to move away from Jupiter again, now Jupiter’s pulling back on it. It should be slowing back down. Shouldn’t you just end up with the same velocity? It’s like going down a hill and then back up it on the other side, shouldn’t you end up going the same speed you were going before?

Pamela: That would be exactly right if the object you were having the gravity assist from wasn’t moving.
 
The key is you are gravitationally falling into the gravity hole of some object in motion. If it’s not in motion, you go in, come back out and your energy hasn’t changed at all. If you imagine a completely frictionless, gently curved valley in the road. You go down a hill, up a hill, no friction occurs so you’re going the same speed on both sides of the hill even though you speed up going in and slow down going up… it all cancels out in the end.
 
The catch is, if the object’s moving, the amount of time that it is either able to gravitationally pull on you to speed you up or gravitationally pull on you to slow you down changes. If you’re moving in the same direction as the object that’s giving you the gravitational assist, as you’re moving toward it, it’s saying “yes! Catch up with me!� and pulling on you to get you to catch up to it. So the whole time, you’re approaching it, it’s running away from you. As it’s running away, it’s pulling on you to help you catch up.
 
Once you catch up to it, you’ve gained all this velocity, so you’re able to zip away from it with extra velocity you didn’t have before, because the extra time you had catching up with it lead to you getting some of its velocity and spending extra time falling in and not extra time falling out.

Fraser: So, you’re slowing down Jupiter by a teeny-tiny little bit, to slow it down in its orbit, and its speeding you up to pull you up to its speed.

Pamela: Yes.

Fraser: Right. So the amount that you get falling into it and the moving back away from it do cancel out, but it’s that process where it’s pulling you up to its speed in the orbit which is what adds to your velocity.

Pamela: If you’re going in opposite directions, then you end up putting the extra effort into slowing down to meet its speed. Then you end up going slower on the other side. Same thing.

Fraser: Right, and I know the MESSENGER space craft is using that method to be able to go into orbit around Mercury.

Pamela: Yes.

Fraser: They’re using this process to be able to slow themselves down, as well – if you just go the opposite direction, you slow yourself down.
 
That totally makes sense. I honestly didn’t have it thought through, so thank you.

Pamela: It’s a really cool affect.

Fraser: You know what, I said that was the last one, but we’ve enough time for one last, quick little question. I think this is a quick one. Rich from New York wants to know “if the Sun were to suddenly vanish, would we feel the effects of gravity instantaneously, or would it take approximately 8 minutes, just like light?�

Pamela: It would take 8 minutes, just like light. Fast enough?

Fraser: The speed of gravity is the speed of light. If the Sun disappeared, we would see the light disappear and we’d also suddenly feel the gravity disappear.

Pamela: It would appear as if all of a sudden all the stars became visible and they’re moving in the wrong way. That’s kind of cool.

Fraser: Yeah.
 
And that effect works the same for us moving around the Milky Way, the Moon going around the Earth… it waits for the speed of gravity. Cool.
 
I think that plays into our recent show about gravity waves, that’s what the whole trick is about. You’re watching as waves of gravity are released from objects as they wash over the planet. That’s it – that was quick.

Pamela: Cool.

Fraser: Perfect. I think that covers everything.

Fraser Cain: Last week we talked about tidal forces within our solar system. This week we’re going to expand our view and encompass the entire universe. Some of the most dramatic events originate from tidal forces caused by gravity: other worlds, galaxies, black holes and even entire clusters of galaxies are under this influence.
 
All right Pamela; let’s give a quick recap. What are tidal forces?

Dr. Pamela Gay: Tidal forces are what you get when you take an object and you put it next to something that exerts a gravitational pull. It has its own self-gravity hopefully holding it together, and the side of it that’s closest to that massive object is getting sucked toward the massive object. This can cause distortions, it can even cause destruction of things.

Fraser: So the tidal forces are the differences in gravity that matter experiences across an object.

Pamela: Yes.

Fraser: So in the example of the Earth, the water on one side of the Earth is experiencing more gravity than the water on the other side of the Earth.

Pamela: Yes.

Fraser: All right, and it’s that difference that makes things go crazy.
 
So let’s go to another solar system and let’s see some things that could be experiencing tidal forces that we don’t have here.

Pamela: Let’s not go to any specific solar system, because there’s all these things called hot Jupiters and they’re all over the place. Currently we know of over 300 planets orbiting other stars. Many of these planets are bigger than Jupiter and have orbits smaller than Mercury’s orbit.
 
So we have these giant worlds really close in to their stars and they have significant amounts of mass. As they orbit their stars, lots of weird things can happen.
 
First of all, they can create tides on the surface of the stars. They can actually disrupt and change the physics that controls the outer-most layers of the stars, just by yanking on the stars gravitationally.

Fraser: When you think about the way these planets are discovered, because they’re yanking at their stars with such a high amount of gravity that the velocity of the star is moving back and forth, toward and away from us that it can be detected, it’s got to be causing some pretty serious tidal forces.

Pamela: We have these planets zipping around their stars on orbits that are 3 days, 10 days – really, really short orbits. The stars themselves often rotate on tens of days scales – 20, 30 days. So as the planet zips around, it’s moving faster than the surface of the star is moving, and this can cause the star’s surface to move out toward these Jupiter-mass (or larger) hot planets.

Fraser: So would you get a bulge on the star that follows the planet, or would you get more like what we have on earth, where the water moves around or changes its height but it’s fairly evenly distributed on the side that’s facing toward the Moon?

Pamela: We’re still trying to sort that out. Unfortunately we can’t just go and take a picture of it, so a lot of what we’re dealing with is computer simulations where we see all sorts of slight oddities in the behaviours of these stars. We’re translating these slight oddities into the idea that there must be tides.
 
Gravitationally, it makes sense. If you get two masses that close, they’re going to start distorting one another’s shape. In the most extreme cases, you actually end up with the planet getting part of its surface ripped off and ripped toward the star.

Fraser: Now, we talked about what’s happening with the star, but what’s happening with the planets?

Pamela: The planets are getting forced to constantly keep the exact same face toward the star.

Fraser: So they’re tidally locked.

Pamela: They’re tidally locked. This means that one side of the planet might be hundreds of degrees in temperature, while the other side is not just below freezing, but it’s down around the temperatures of liquid nitrogen.
 
So you can end up with these massive convection events going on if you have a planet with an atmosphere. This is sort of like if you go into a room where you have air conditioners that are venting at the ceiling. You have the cold air falling and the hot air rising, so you end up with circulation of the air naturally. Here, you have one side of the planet has a lot of cold, the other side of the planet has a lot of hot, and this can end up causing massive circulating winds on these planets (if they have atmospheres).

Fraser: I heard the winds can go super-sonic.

Pamela: We’re still figuring it out, and they can go amazing speeds, we’re thinking.

Fraser: Yeah, thousands of kilometres an hour – the strongest winds ever seen in the universe.

Pamela: This is created by tidal locking and extreme heating. If they get a little bit closer, their atmosphere starts getting pulled off.
 
This can also happen in binary stars. If you have two binary stars that get too close to one another, you can actually end up with them swapping mass back and forth between them.

Fraser: So the two stars would be bulged toward each other. Would the stars be inside the Roche limit of one another?

Pamela: We look at this in terms of gravity and potentials. If you take two objects and bring them close enough to one another, there’s going to be this shape around them (you have to think in three dimensions, unfortunately). If you are walking along this surface, you’re getting pulled the exact same amount by both objects. There’s this point (the Lagrange-1 point), between the two objects where you’re balanced between the two.
 
Now, if gravity pulls on a star such that its mass exactly fills this equi-potential surface, this surface where the gravitational pull is the same everywhere, and something hiccups, you can end up with mass flowing off that surface, and toward the other object.
 
There are actually binary systems out there that constantly swap mass back and forth between two stars. You can end up with two stars, in a nice, happy binary system, evolving along and if they don’t have the exact same mass, one of them will bloat up as a red dwarf first.
 
When it bloats up, it might, as it changes in size, overflow its limits and pass the mass to the other star. Or it might successfully going on evolving, eventually shrink back down, bloat back up, go through all sorts of evolutionary stages until it becomes a white dwarf.
 
At this point, it’s going to lose some of its atmosphere, and this is going to change how the two stars interact with one another. So in the process of becoming a white dwarf, a star basically sheds the outer parts of its atmosphere and only keeps the core.

Fraser: So this must change its mass, then.

Pamela: It changes the mass, and it changes how the two objects orbit.
 
Now, if that white dwarf ends up still fairly close to that other star, when that other star then expands back out in its evolution of becoming a red dwarf star, that white dwarf, that now dead object, might be able to grab that mass that’s starting to overflow this Roche-lob, this equi-potential surface, and suck it over.
 
If it sucks enough mass over, it might actually bloat itself back out and become a normal burning star in a second generation of life. It’s actually possible for a star to get re-kindled if it grabs mass in just the right way.

Fraser: That’s amazing. There’s a just the wrong way for it to grab mass too, isn’t there?

Pamela: Exactly. So if it grabs mass the wrong way, instead what you end up with is an exploding system. This is where we get the type Ia supernovae.
 
So if you instead take a white dwarf star, throw mass onto it and don’t trigger nice, happy nuclear reactions that cause the star to bloat back out and be a real star, you can end up, instead, with the mass piling up and not having anything to support it.
 
In a nice, happy, normal star, we have nuclear reactions going on that are generating light. That light pushes out the outer layers of the star, supporting the star. If you don’t have that light exerting this pressure, then gravity is constantly trying to squish the star.
 
If you throw too much mass together, that pushing from gravity, that contracting of the mass from gravity, is eventually going to cause it to explode like a nuclear bomb. In this case, that nuclear explosion is a type Ia supernova. This only happens in binary systems where you have a white dwarf grabbing mass off of a binary companion that has overflowed its Roche lobe.

Fraser: Are there any other interesting kinds of solar systems, or any interesting situations you could have with tidal forces?

Pamela: There’s always black holes.

Fraser: All right!

Pamela: (laughing) So, with a black hole you can end up with the whole filling of the Roche lob, stripping of stars, but here things get taken to the extreme (with black holes everything gets taken to the extreme).
 
Say some nice, friendly, lost, asteroid/planet/some object isn’t politely orbiting a black hole, but is rather wandering through the black hole’s solar system, and is sort of on a semi-collision course. As that object heads toward the black hole, it’s going o get elongated. As it starts to fall into the black hole, it’s going to get elongated to the point that you end up with an effect called spaghettification (which is perhaps one of the funnest things we’ve named in astronomy, most things have terribly boring names).

Fraser: Hold on a second, you’ve got it getting elongated because the force of gravity on the front of the object is different from the force of gravity on the back of the object?

Pamela: Exactly. If you have a piece of Silly Putty, and pull on just one edge of the Silly Putty, it’s going to stretch out.

Fraser: Okay, but I’m a little confused. If I understand correctly, if you take two objects under the force of gravity, and you drop them, they’re going to fall toward that object at the same speed.

Pamela: The catch is, with these two objects falling at the same speed, we’re assuming they’re structurally rigid, they’re structurally holding themselves together. It’s their centres of mass (in a human being, the belly-button) that are falling at the same speed. Now, something that is closer is going to get pulled on more, so it’s going to have a greater acceleration than something that’s further away.
 
So in theory, if I drop an object from a height of 10m while standing at the top of Mount Everest, that object is going to take a different period of time to fall 10m than an object that I drop from a submarine sitting on the bottom of a ocean trench – I don’t think you can actually do this, I think the sub would probably not survive – but if I had a sub that had a 10m height that I could drop something in, that I planted at the bottom of the ocean, that object would fall faster. It all depends on how far you are from the centre.

Fraser: I see, so in the case of a black hole that makes a big difference.

Pamela: So my feet might be falling faster than my head, and my body can’t structurally hold itself together. This works with people, it works with spaceships, it works with asteroids. Pretty much anything you throw at a black hole.

Fraser: You kindly chose an asteroid, but go on, use a person. Let’s get spaghettified!

Pamela: (laughing) Okay, so you throw a person at a black hole. You assume they’re in a fairly wussy spacesuit that will shred itself if you pull on it hard enough. As they fall into the black hole, the feet get pulled on much more strongly than the head, so they experience a greater acceleration. The body gets stretched out.
 
It’s going to slowly render itself asunder (another one of those fun phrases that comes out of science now and then). It’s basically going to get torn into multiple pieces, might break apart at the weakest point in the body (which is about the waistline) first. Legs, head… all of these things are going to slowly come apart.
 
Each of these parts is going to get stretched out and made more skinny in the process, sort of like as you pull on your Silly Putty, it gets skinnier as the pieces move further and further apart. Eventually you’re just going to end up with this atom-wide chain of former-human being atoms falling into a black hole.

Fraser: This whole process is only going to happen in a millisecond, right? So don’t worry about the horror of it.

Pamela: Yeah, you’re not going to be aware of what’s happening to you.

Fraser: Yeah, just ZIP! And that’s it.
[laughter]
 
But the physicists know what really happened.

Pamela: Oh yeah, and we get to give it fun names.

Fraser: What about larger black holes, like the supermassive black holes?

Pamela: The physics is all the same, it’s just matter of scaling. With the supermassive black holes, you’re going to have, perhaps, entire stars falling in and getting spaghettified in the process.
 
Supermassive black holes, especially in the early universe, can eat things in the most dynamic of ways. Our own galaxy’s supermassive black hole doesn’t have anything in the process of falling in. it’s already gobbled everything nearby that had an unstable orbit, so it’s just sitting there.
 
In the early universe, galaxies had a lot more gas, a lot more dust. Things hadn’t been made into stars as much yet. Everything was still knocking about, so you’d get things on bad trajectories that just happened to send them straight into the centre of black holes.
 
As the material goes into the black holes, it first gets shredded into an accretion disk, then as the accretion disk falls in, some of that material is going to get spit out along magnetic poles. So you have these magnetic fields getting driven by accretion disks, everything’s in motion, there’s lots of high-energy physics going on and you occasionally have, basically supermassive black hole burps that can just send high-energy shock waves through the entire inner parts of galaxies.
 
So this isn’t just tidal forces in action, this is tidal forces combined with magnetic fields, combined with jets, combined with all sorts of really neat frictional forces in the accretion disks… lots of dynamic forces and lots of death and destruction.

Fraser: All right, so let’s talk about how galaxies interact. I think you’d mentioned there was going to be some galactic interactions.

Pamela: Anytime you end up with any two masses interacting, you have tidal forces. Sometimes, when astronomers say, “an object,” we’re actually referring to families of objects: a galaxy is a family of stars, gas and dust that are all gravitationally bound together. It’s possible to break these families up.
 
Our own galaxy is in the process of disrupting a number of different things, for instance there’s this little dwarf galaxy called Carina that we’re in the process of slowly shredding as it orbits in the halo of the Milky Way Galaxy. As it goes along, it’s evolving from being a nice, friendly, (we think) originally completely elliptical or spheroidal collection of stars, to being this stream that marks the orbit of where Carina used to happily revolve around our Milky Way Galaxy.

Fraser: I guess it’s a similar situation to Comet Shoemaker-Levy 9, where it used to be a comet, got to close to Jupiter and, I guess, overcame the Roche limit and got broken apart into a stream of objects. That’s just what’s happening to this Carina galaxy, right?

Pamela: Exactly. We also end up with what are called tidal tales in some of the most spectacular-looking galaxy interactions. For instance, the antennae galaxies. As these two galaxies approached each other, the leading edges got attracted much more strongly, so they reached out for one another, and ended up with these leading arms reach out to grab each other as the galaxies approach.
 
At the same time, you have stars on the backside of the galaxy that aren’t getting pulled on as much. They’re just hanging out, lagging behind. So you have these two arms streaming behind the galaxies, and you end up with these amazing leading and trailing arms as gravity elongates galaxies during these tidal interactions.
 
These tidal arms, these tidal tails, can end up twisting and spiralling as the two galaxies don’t necessarily go for head-on collisions, but perhaps initially go past each other and gravity in these side-swipes is actually able to create these streams with really fascinating spiral shapes.

Fraser: I’ve seen some amazing simulations of gravitational interactions where they’re simulating all the stars in two galaxies, and then have them ram into each other or pass by each other. The dynamics, the tidal tails that come out – it’s almost like sprays, like if you just took a galaxy and sprayed it. It’s quite amazing to see what the interactions turn out to be.

Pamela: Josh Barnes of the University of Hawaii has some really amazing to look at simulations on his website. You can go in, and see for instance, what did the Mice galaxies look like through the process of their evolution. He can basically say, “I know what this looks like today, let’s figure out how it got there.” He can reverse-engineer the formation of these gorgeous, self-destructing galaxies.
 
We can also move this forward, and since we know what the Milky Way and Andromeda galaxies look like today, we can imagine what they’ll look like in the process of collision in the future. How are tidal effects going to cause our galaxies to stream out and disrupt each other? How is the gas and dust going to get moved around? What’s going to trigger star formation, and what’s going to kill star formation?

Fraser: What is the final result, after all these interactions settle down – what do you get?

Pamela: Eventually in every case, you end up with objects basically getting torn apart and settling into a nice, spherical shape.
 
The universe seems to want everything to eventually be a sphere. This may, perhaps, be Aristotle’s greatest revenge. He said the most perfect shape is a sphere, and the universe seems to be attempting to comply.
 
So you take things, shred them apart, reform them and they generally reform into elliptical and spherical shapes.

Fraser: So eventually, galaxies will just be spheres as much as they can be, but at the same time if they’re rotating they’re going to flatten out.

Pamela: Exactly. Now with some of these mergers, you can actually end up with giant elliptical galaxies that don’t have a collective rotation in any one particular direction. So you have stars that are al mutually orbiting the same central point, but the orbits are completely chaotic in their orientation and you can end up with truly spherical systems that have no net rotation at all.

Fraser: So can we go larger, then? To the biggest structures in the universe?

Pamela: We also have tidal effects as clusters fall into one another. We can look at how the dust from one cluster – and the gasses in particular (gases are much easier to see, we use the Chandra X Ray Observatory to look for hot gas as things collide), how does the gas and dust in clusters interact as two clusters merge? How do the galaxies get distributed as the galaxy clusters merge. It’s this constant story of things getting stretched out as they pull one another together and then in the process of the collision settle back down to spherical shapes.

Fraser: I guess instead of the spray of stars, we have sprays of entire galaxies.

Pamela: We have sprays of galaxies, and we have sprays of gas and dust, and even dark matter. That’s one of the coolest things. We can actually see the dark matter getting in on the gravitational interactions, thanks to some of the new work done using gravitational lensing.

Fraser: That was going to be my next question. What impact does the dark matter have on the tidal forces? I know the dark matter doesn’t clump into objects in the same way that normal matter does.

Pamela: But the gravitational pull of a cluster’s dark matter can cause something coming toward it to get stretched out, to get elongated. It can do the gravitational pulling that causes the tidal effects. It can also get elongated and tidally stretched out itself. It does all sorts of neat gravitational effects, and gets effected by gravity. We just don’t see any of the heating and getting shredded and things like that happening with dark matter. It’s just this happy to be there, non-interacting stuff.

Fraser: All right, was there anything else we missed? We covered a pretty big chunk of the universe there.

Pamela: From planets to galaxy clusters, tidal affects are just about everywhere. While saying it’s being tidally-affected is about the most boring-sounding thing I can say, tidal affects are some of the neatest and most ignored bits of physics, and it’s all about differential-pull on an object.

Fraser: I’ll think about that next time we go to the beach.

Pamela: Exactly.

Fraser Cain: Consider the following: we’ve got tides here on Earth, there’s the fact that the Moon only shows one face to the Earth, we’ve got volcanoes on Io, and ice geysers on Enceladus, and all these phenomena originate from a common cause: the force of gravity stretching across space to tug at another world.
 
So Pamela, those are all connected. Explain how.

Pamela Gay: There’s this thing called tidal forces. It’s a name that hides a lot of really cool physics.
 
So here on the Earth, we have gravity from the Earth itself pulling us down. If the planet Earth was hanging out completely by its lonesome, isolated from everything else in the universe, you could walk around the entire planet and the pull of gravity on your body would be exactly the same everywhere (ignoring effects due to being on top of a mountain, in the bottom of a valley or something).
 
In this isolated-Earth situation, the oceans would be perfectly smooth other than waves driven by the rotation of the planet. There wouldn’t be any tides: all the waves would have the same height (barring wave interference things, which is completely different physics). The waves would come up the beach the same amount (ignoring weather – there’s all these things you have to ignore when talking about the planet Earth, because it moves and has weather.)
 
Without a moon, our planet would be a lot more boring. Now, if you bring the Moon in, as the Earth rotates, different parts of the planet are closer and farther from the Moon. The Moon exerts its own gravitational pull on the planet. So if you’re on the side of the planet that’s closest to the Moon, you’re getting pulled toward the Moon and you’re getting pulled toward the Earth.
 
The Earth wins in this battle, which is why we stay on the planet Earth and we don’t float off into space. But this additional pull from the Moon causes us to get lifted. If you’re an ocean you can get lifted several feet toward the Moon. The planet Earth itself, if you’re standing on a rocky section (which is usually what we stand on) can get lifted as much as 30cm.
 
So the entire planet flexes toward the Moon.

Fraser: I thought it was only the oceans that were moving toward the Moon, but the actual rock of the planet is doing it too?

Pamela: The actual rock – our chairs are moving up and down, twice a day, roughly 30cm in response to the Moon.

Fraser: Wouldn’t you feel that?

Pamela: It’s a gradual thing. If I move you up and down over 12 hours by 30cm (that’s only about a foot), you’ll never notice it.

Fraser: Wow.

Pamela: So if you do anything slowly enough, no one notices.

Fraser: What are we doing to the Moon?

Pamela: The Moon is hanging out, completely locked to the Earth. Since it’s not rotating relative to the Earth, it maintains the same shape all the time as it goes around.

Fraser: Is that our fault?

Pamela: That’s our fault. The Moon isn’t a perfect sphere, and the part of it that’s a little bit denser, the part of it that’s a little bit bulged, always points toward the Earth.
 
Once upon a time, the Moon was probably rotating, but as things rotate, if they have a part that’s a little bit bigger than another part, that bigger part creates a gravitational friction. This is actually still happening with the Earth and the Moon. The Earth’s rotation is getting slowed by the tidal effects of the Moon.
 
As our planet fluxes toward the Moon, it tries to rotate away. Our planet is rotating on about a 24 hour period. As the bulgy part rotates past the Moon, the Moon tries to grab onto that and creates what’s called a torque. The Moon gravitationally pulling on the bulged part of the Earth (which it created with its gravity) causes the Earth’s rotation to slow down, as the Moon tries to pull that bulge backwards toward it more and more.

Fraser: I could imagine, say you had a ball with a little magnet attached to it on one side, and then you had another magnet, and you spun the one ball (let’s say they couldn’t actually click together). The one with the magnet on it would spin around and then it might get to the point where the spin is so slow that the magnet actually pulls it back and then the two magnets are just facing each other, and that’s it; there’s no more spinning of the ball.

Pamela: That’s exactly what’s happening with the Earth and the Moon.
 
Now what’s weird about this (it’s not weird physically, but it’s weird to think about), because the Earth is slowing down in it’s rotation (and there’s all sorts of conservative forces going on), as the Earth slows down, the Moon has to move further away from the Earth to conserve angular momentum. So as our planet slows in its rotation, the Moon moves further and further away.
 
Currently we have solar and lunar eclipses because the Moon is able to completely fit within the Earth’s shadow (which is when we get a lunar eclipse), and the Moon is (most of the time) able to completely cover the Sun (causing a solar eclipse). As the Moon moves further away, it’s going to get smaller in apparent size, just like when you watch a friend walk away on a sidewalk, your friend appears to get smaller and smaller in size as they move to a greater distance.
 
Now, as the Moon moves away, it’s eventually not going to be able to block the entire face of the Sun, and we’re going to stop having complete solar eclipses, and instead we’re going to end up with solar donuts whenever we have annual eclipses.

Fraser: That’s right, and we talked about that in our episode about where the Moon came from. It’s a total fluke that the size of the Moon matches the size of the Sun in the sky perfectly. It won’t be that way millions of years down the road.

Pamela: Sometimes we just get lucky. In this one case, we happen to live in just the right time to see something pretty cool happening in the sky.

Fraser: Okay, so apart from the tides, do the tidal forces actually cause an effect to our planet or to the Moon?

Pamela: Between the Earth and the Moon, there aren’t that many dynamic affects, but here we’re dealing with two fairly large objects that are gravitationally holding themselves together fairly effectively.
 
If you move out to other places in the solar system, where you have larger mass differences between the objects involved, you can actually start to get some pretty dynamic things happening.
 
For instance, the poor, innocent moon Io, which orbits Jupiter, is constantly getting squished and stretched by the differing gravitational pulls it experiences not just from Jupiter but the other Moons that are orbiting Jupiter as well (Europa, Callisto, Ganymede). All these different moons are playing tug-of-war with Io, and this causes it to have a molten core and dynamic volcanoes and it’s a really amazing object to look at images of.

Fraser: The forces have to be much different than the fairly tame ones we’ve got here on Earth.

Pamela: Yes, and in this case… if Io was just by itself, happily orbiting Jupiter, it would settle into a stable orbit where it probably always had the same side facing Jupiter, and not much would be happening. Because Europa, Callisto and Ganymede are going past it on further out orbits, it can end up with times where it’s getting stretched out between Jupiter and three other Moons, and its orbit is constantly changing as It’s getting pulled out by the other Moons and pulled in by Jupiter. As it changes its distance from Jupiter, Jupiter also changes its shape. All of this constant stretching ends up heating the inside of the planet: it’s compression heating.

Fraser: You mentioned it has volcanoes, but that’s a bit of an understatement for Io.

Pamela: It has some of the largest, most dynamic volcanoes in the solar system. This is a planet that doesn’t have all that many craters, because the surface is constantly getting re-coated in lava. We’ve actually been able to see these volcanoes erupting constantly, using both satellites and occasionally we can even catch them exploding using the Hubble Space Telescope.
 
The entire moon looks like some kind of mad chemist’s experiment as its volcanoes are constantly emerging, erupting, resurfacing and changing the entire surface of the moon.

Fraser: So what impact is happening to the rest of Jupiter’s moons? It’s got to have quite a fearsome tidal effect on them as well.

Pamela: Europa is also experiencing this tidal heating of its core. Here we don’t end up with anything quite as exciting, but with Europa, the constant, slight stretching and expanding of the planet is just enough to keep its inner parts liquid water. We don’t know if this is strictly H2O water, there’s other chemistries involved.
 
The surface is frozen, but beneath this frozen surface there’s liquid, and this liquid is able to come through the surface and cause constant resurfacing of this moon as well. It leads to all sorts of neat structures where you end up with spiral patterns through the ice that are marking how the planet’s orbit and orientation toward Jupiter have changed over time. You end up with cracking and all sorts of really neat effects in the surface that are caused just by gravity tugging on this giant ice and liquid ball orbiting Jupiter.

Fraser: So unlike Io, which is so torn up that volcanoes are bursting out of the surface, Europa is still being maintained as fairly warm, so there’s believed to be an ocean of liquid water on the surface, with a crusty shell of ice surrounding that. How thick is that shell believed to be?

Pamela: It’s measured in metres. It’s nothing we can’t dig through with a space probe. One of the really cool things about Europa is it’s possible for us to send probes to Europa, tunnel through the ice and explore the water beneath the ice. It’s some place that might actually be possible to have life.

Fraser: Wherever they find water on Earth, they find life.

Pamela: And tidal stirring mixes up the chemicals, making it possible for nutrients to move around, making it possible for thermal dynamics to exist (where you have a hot area and a cold area exchanging energy) everything is there to encourage all sorts of neat chemical reactions to take place.

Fraser: Now is there anything else in the Jovian system that’s interesting, or should we move further out?

Pamela: I think the next set of really neat objects are all orbiting Saturn, so let’s move out one more planet in the solar system.
 
Around Saturn, we have this moon called Enceladus. It’s generally a boring little moon, but if you watch it closely, and you watch it with a satellite that’s orbiting in the Saturnian system, you’ll see geysers going off. These geysers are (again), being caused by tidal heating of the planet. As the planet is getting flexed by the differences in the politic experiences from Saturn on its slightly elliptical orbit, it’s getting pulled on by other things in the system – it’s getting heated. This heat, and the fluid that’s made fluid by the heating, has to escape so it escapes as geysers.

Fraser: So this is less extreme than what’s going on, on Io, but still, this process is keeping it warm. What affect do these geysers have? I’ve heard they might even be helping to create the rings.

Pamela: When the geysers go off, they’re shooting liquid out into the cold of space. Now the thing is, just like a snow machine, when you spray mist into the air, it freezes into ice crystals. These geysers are basically the largest snow-making machines in the solar system.
 
This ice then gets gravitationally trapped and it ends up forming part of the material in the rings. What’s cool is the distribution of these particles actually forms a kind of double-ring. You don’t end up with a perfectly flat ring, instead you end up with two rings slightly above and below one another.

Fraser: Astronomers were able to trace back these particles right back to Enceladus.

Pamela: Exactly. So we know where they come from, we know what’s creating them, and we understand the physics behind them. It’s just a really neat thing to get to experience because these are all discoveries that have just been made in the past year and a half. This was a discovery made back in March of 2006. Now we’re starting to find geysers around other moons as well.
 
Who’s to know how may of these things we’re going to end up finding? It’s an active and dynamic solar system out there, and in these cases, what we’re seeing isn’t created by the Sun heating things up, but by gravity heating things up. We’ve identified a new source of heat that can be used to cause planets and moons to be geologically active .

Fraser: If there is life, that could be almost like a completely different ecosystem from the one that’s dependent on the Sun.

Pamela: This would be similar to the life that we have in our deep ocean trenches where underwater heat vents and volcanoes are creating the heat and the nutrients necessary for life to exist in the depths of the ocean where sunlight is unable to penetrate.
 
So we could find twins to our underwater life on these tidally-heated worlds out in the outer solar system.

Fraser: Is there anything else in the solar system – our solar system – that you thought was relevant?

Pamela: So far we’ve been talking about things that are nice and safely held together gravitationally but are getting heated, distorted or having their orbits changed. What we haven’t talked about is how tidal effects can actually destroy things – which is kind of cool (death and destruction is always cool).

Fraser: That’s what I like to hear!
 
[laughter]

Pamela: So, the planet Mars has these two little moons, Phobos and Demos. They’re not at all like our moon, they actually resemble a couple of potatoes orbiting the planet. Now these potatoes have two very different orbits. Phobos is extremely close to the surface of Mars. It’s in fact so close that the only thing holding it together right now is the chemical connections between the atoms in the moon.
 
The moon is so close to the planet that its self-gravity, the ability of the moon’s mass to hold itself together, is actually overwhelmed by Mars’ gravity. So if there weren’t the atomic and molecular connections between the atoms in the moon, the moon would completely shatter and we’d end up with basically a Phobos ring around Mars.

Fraser: Is that going to happen?

Pamela: It’s probably actually going to happen.
 
Now, there’s two different ways that a system can evolve spatially. With our Earth and Moon, the Earth is rotating faster than the Moon is orbiting. As the Earth rotates it’s getting slowed in its rotation by the Moon and the Moon is moving further and further away to conserve angular momentum.
 
In the Mars-Phobos system, Phobos is actually orbiting Mars faster than Mars is rotation. As it goes around, the gravitational drag it’s experiencing is actually causing it to spiral inwards. So here we have the moon moving inwards and as it does, the gravitational tidal forces are getting stronger and stronger and stronger.
 
Currently, it’s about 1400km inside of what’s called the Roche limit. The Roche limit is the point at which an object is exactly held together by its own gravity, versus if it goes any closer then the gravity of whatever it’s orbiting starts to be stronger than its self-gravity. So it’s inside that limit. As it continues to migrate in, the gravitational tidal forces are going to overcome the molecular forces and pull the planet apart.
 
We don’t know exactly when that will happen. We don’t know how strong the molecular bonds are between the different rocks, gravel and constituencies that make up this asteroid. It’s sort of like if you pull a stick out of your yard, some sticks are easier to break in half than others.
 
We know it’s going to happen in the next 50 million years, because if it doesn’t, Phobos is going to crash into the surface of Mars (which is interesting in its own right).

Fraser: But that will end it anyway.
 
[laughter]

Pamela: That will end it anyway.
 
So sometime within the next 50 million years, Phobos is going to get completely torn apart (gravitationally) by tidal disruption.

Fraser: Now, one planet you haven’t mentioned, but I think there must be some impact, is Mercury.

Pamela: Mercury has this really neat orbit rotation dynamic going on. Mercury has an orbit that is the most elliptical in shape of all the orbits in the solar system for planets – Pluto (former planet, not a real planet) has a more elliptical orbit, but of the eight standard planets, Mercury has the most elliptical orbit.
 
As it goes through this orbit, it rotates one and a half times every time it goes around the Sun. this means that for every two years on Mercury, someone standing on the planet would experience three days. This weird 3:2 resonance of day length to year length is caused by the planet actually being egg-shaped.
 
Normally we expect that when things are tidally-locked, there’s a 1:1 resonance, like with the Moon (the Moon rotates about its axis one time for every one time that it goes all the way around the planet Earth. This is why we always see the same face, but if you compare what face of the Moon is facing the Sun, you can see the Moon actually rotates all the way around its axis).

Fraser: Right, the Moon has a far side, but it doesn’t have a dark side.

Pamela: Exactly.

Fraser: I guess if Mercury was to end up being tidally locked to the Sun, it would have a dark side.

Pamela: Exactly.
 
The reason it’s not actually in a 1:1 resonance like our Moon is because the shape of its orbit is changing constantly. Mercury is this little tiny planet that’s getting yanked on not just by our Sun, but by all the other planets in our solar system. As it gets yanked this way and that way, its orbit is constantly changing a little bit. It’s this constant changing and all the weird dynamics with its egg-shaped planet-ness that leads it to have a 3:2 resonance instead of a 1:1 resonance (It’s a lot of really complicated math, that’s really neat).
 
This is again a fairly new discovery. It’s only been in the past 100 years that we figured out Mercury isn’t always showing us the same side. We thought it was tidally locked, with this 1:1 resonance.
 
The reason we thought this is Mercury is really hard to observe. At most it gets about 28 degrees away from the Sun. this means if the Sun has just ducked below the horizon, if you hold your fist out at arm’s length, with your little finger on the horizon and place your other fist on top of your thumb and walk up three fists from the horizon, Mercury never gets more than those three fists above the horizon at sunset. That’s under ideal circumstances; most of the time it’s not that high in the sky. The only time it’s at its best viewing, because of this weird resonance, it’s also showing us the exact same side.
 
So whenever we looked at it under ideal circumstances, we were always seeing the same face of Mercury. It was only after we developed radar technologies and were able to shoot radar beams off Mercury, we were able to see that it actually is orbiting faster than it’s rotating.

Fraser: All right. With a lot of the things we look at, we can try and predict into the future what’s going to happen. Are there going to be some interesting situations in the future where there will be these tidal effects that we don’t see today?

Pamela: It’s hard to predict exactly what object is going to have what tidal effect, but there are certain things we know happen on a regular basis.
 
For instance, the comet Shoemaker-Levy 9 was torn into a bunch of different pieces through tidal disruption by the planet Jupiter. We got to see this comet get disrupted and then plunge into the surface of Jupiter. That’s kind of cool.
 
These disruptions of objects happen on a fairly regular basis, we think. As we look around the solar system, we see all these different objects that have craters we think were formed at the exact same time – these are basically chains of craters that appear to have been formed by similarly sized objects.

Fraser: I’ve seen those pictures. It looks like someone took a machine gun to the Moon

Pamela: Exactly.

Fraser: And there’s maybe 10 craters all in a row.

Pamela: We think what has happened is we’re seeing the death march of an object that first got gravitationally shredded and then gravitationally sucked into something and destroyed in the process.
 
So these are objects that had a very hard life.

Fraser: Would that be an example of say, a comet or passing within that Roche limit?

Pamela: That’s exactly what happened. A comet got within the Roche limit of some object and it got torn apart.
 
Now, there’s a different Roche limit for every pair of objects. You have to look at the two masses of the objects, the distances between the objects and take all of these different things into account, and the tensile strength plays in.
 
If you throw an asteroid that is very loosely held together, it’s basically a conglomeration of rocks that are just barely gravitationally held together, that’s going to get shredded a lot more easily than an iron-based metallic asteroid that’s basically a large chunk of metal.
 
Different objects will get torn apart in slightly different ways, but there’s lots of stuff out there just waiting to get shredded. This happens to comets, it happens to asteroids. There are a few really weird-shaped asteroids that are extremely elongated, and they’re just waiting to tear themselves apart.

Fraser: Well that was great. Now this is only half this conversation, because we’ve only covered the solar system, but in fact these events span the entire universe. Next week we’ll talk about some of the tidal forces we can see acting outside of our solar system.

Pamela: Sounds like a great plan.

Fraser Cain: You probably don’t realise it, but magnetic fields are everywhere. We’re not talking about the magnets in your speakers, your electronic equipment or on the fridge door. We’re talking about the gigantic magnetic fields that surround planets, stars, galaxies and some of the most exotic objects in the Universe.
 
Okay Pamela. So first, let’s just figure out a basic definition: what is a magnetic field?

Dr. Pamela Gay: A magnetic field is related to the electromagnetic force between two objects, where one of those objects involves charged particles that are in motion. It’s really, unfortunately, something there’s not a nice, one sentence, clear-cut definition of. You get a magnetic field anytime a charge moves. This means that when you’re dealing with a refrigerator magnet, what you’re seeing as a force that attaches you magnet to the refrigerator is resulting from all the little electrons in the atoms in the magnet all moving, and that motion is able to exert a force that holds the magnet on the refrigerator.

Fraser: In the situation of the magnet on the refrigerator, they’re moving in a common direction, right?

Pamela: All the atoms manage to (or most of the atoms) manage to line up so the little electrons are all orbiting in patterns that are aligned with one another, and those alignments create a unified magnetic force.

Fraser: So if I have a rock – just a regular rock, not a magnetic rock – it has atoms and those atoms all have electrons whizzing around them, but because they’re not lined up, the rock doesn’t stick to my fridge door.

Pamela: Exactly. All those electrons are creating their own magnetic force, but if all those forces are aligned in different directions and pulling in different directions, you end up with a net force of about zero. It’s sort of like if you have a whole bunch of different people pulling on a pillow from different sides, the pillow’s not going to go anywhere, because the net force cancels out.

Fraser: That’s the weirdest analogy you’ve used so far.

Pamela: Okay!
 
[laughter]

Fraser: How’s it relate to electric fields? We’ve got electricity, we’ve got electrons moving through wires, and there’s a connection between that and magnetism, right?

Pamela: Every electron, every proton, every charged particle has both an electric field associated with it, and (if it’s in motion) a magnetic field associated with it. When we look at the net electromagnetic force, it’s the sum of those two different components, and the electric field and magnetic field are always perpendicular to one another. For instance, a photon (a particle of light) moving through space is going to have both an electric field and a magnetic field that are perpendicular to one another, and perpendicular to the direction of the photon’s motion (it’s very mathematically ugly).

Fraser: Yeah, well we’re not going to get into the math. I’m sure we’ll link to some stuff in the show notes. More importantly, we want to talk about how a magnetic field can get around a large object. As I said, if I have a rock and the rock won’t stick to my fridge, how come the Earth can have a magnetic field? Can I stick the Earth to my fridge?

Pamela: Well, unfortunately the Earth’s magnetic field is a lot weaker than the magnetic field of, well, your standard three-year-old’s letter ‘L’ that sticks to the fridge quite successfully.
 
The magnetic field of the Earth is coming from (like all of them) charged particles in motion. We have a molten metal core to our planet, and as the molten metal swirls and rotates, it’s motion is (in ways we don’t fully understand) able to create this magnetic field. It’s only because we have a molten core that we have a magnetic field. Eventually our planet is going to cool off enough that the molten metal solidifies, volcanoes go dormant, no more cool funky magma. When that happens, the magnetic field is going to slowly fade away.
 
Over time all magnets lose their magnetism. Initially, when the metal stops moving, there’ll be a residual magnetic field from things that have had their atoms get aligned just by having magnetic field lines pass through them for so long.
 
It’s sort of like if you stick your scissors on top of a fridge magnet, the magnetic field will slowly cause the atoms in the scissors to align one another so your scissors become magnetic. But if you bang your scissors on the counter enough, the atoms will re-randomize themselves so the scissors are no longer magnetic. Our planet will, for awhile, have a residual magnetic field, but over time that will go away.
 
When we look at the planet Mars, once upon a time it had a magnetic field. Today, that magnetic field is gone because the planet has cooled, it no longer has a liquid core, and the residual magnetic field is also gone.

Fraser: Losing your magnetic field is a very bad thing.

Pamela: It’s a very bad thing. We need our magnetic field to protect us from the Sun. as charged particles get flung off the Sun toward the planet Earth, our magnetic field says, “aha, I’ve got you!” grabs the charged particles, and forces the charged particles to move along magnetic field lines that keep them out of our atmosphere, keep them from destroying our atmosphere. As they stream across the magnetosphere, we see these amazing aurora (the northern and southern lights).
 
If we didn’t have that magnetic field we wouldn’t have the northern or southern lights, and those charged particles would hit our atmosphere directly and end up knocking chunks of our atmosphere out into space.

Fraser: So here on Earth, we’re protected by the Earth’s magnetic field, so all those charged particles from space go right around the Earth and don’t hit us. If you were sitting on the surface of Mars, you might as well just be in space. You’re getting hammered by particles from the Sun whether you’re on the ground or up in space.

Pamela: This is also part of the reason why there’s a much higher radiation level on the surface of Mars. Astronauts going to Mars don’t have to worry about the cold nearly as much as they have to worry about the radiation and lack of oxygen. If it was just a lack of oxygen problem, you walk around the surface of Mars wearing a warm jacket and an oxygen mask.
 
You have to worry about the low vacuum of space causing you to bruise violently because of the pressure difference, but in a pinch… you bruise, you run to the next thing, you suffer a little bit, but you survive. The radiation levels you encounter on Mars, that’s a real problem that’s not as easy to defend against. We have to figure out really effective radiation shielding if we want to have people live successfully on the planet Mars.

Fraser: Does the Earth’s magnetic field stay constant? I’ve heard it’s flipped in the past.

Pamela: We don’t fully understand why it does what it does, but yeah. We have geologic indications that when rocks formed at one point in the past, the Earth’s magnetic field was different. As the rocks formed out of molten materials, the magnetic fields within the rocks aligned along the Earth’s magnetic field. Rocks that formed far in the past have a different orientation than the magnetic field of today.
 
We don’t know how often the Earth’s magnetic field flips, or why it flips – we just know that now and then it flips and we can actually observe the north magnetic pole slowly wander over time. Currently it seems to be on its way to Siberia, of all places.

Fraser: That’s an amazing piece of science, that geologists can observe the lava that comes out, and measure its magnetic field. I can imagine what happened: the lava came out, it was still in a liquid state, it got aligned by the Earth’s magnetic field, and then it hardened and created a record like a fossil.

Pamela: That’s pretty much exactly what happens. I have to admit, I’m not a geologist. I don’t know what specific types of volcanoes, what types of instances this occurs in. what I do know is if you take any metal, and you heat it up, and pass a magnetic field through it while it’s at a critical temperature (Curie point) you can end up, as it cools, it will end up gaining the magnetic field that is passing through it and have its own magnetic field when you take it and walk away with it somewhere.
 
At the same time you can take a hunk of metal that’s working perfectly well as a fridge magnet, heat it up, and when you heat it up again to this magical Curie point, if there’s no magnetic field around it will lose its magnetic field. So anytime you heat up material, you can either put in or take out a magnetic field depending on the environment while the metal is cooling off.
 
Naturally occurring magnets come in the form of lodestone, but we can create magnets out of a lot of different types of magnetic materials.

Fraser: Let’s talk about other magnetic fields here in our solar system, because I know we’re not alone in having a magnetosphere.

Pamela: No, in fact magnetospheres are one of those things that crop up all around the solar system. Surprisingly, the most magnetic object in our solar system appears to be the planet Jupiter. Jupiter has a rotating metallic hydrogen interior. This rotating interior gives Jupiter a field that is many times stronger than the Earth.
 
At the surface of the Earth we have a magnetic field of about 0.3-0.6 Gauss. This is the magnetic effect that is just able to move your compass, as long as your compass is nowhere near a refrigerator magnet.
 
On the surface of Jupiter, the magnetic field is more often measured to be between 11 and 14 Gauss at the surface. I have to admit that in trying to look up measurements of Jupiter’s magnetic field, I found numbers all over the place, so when you’re reading these numbers you have to be careful to ask where they’re measuring the field. Are they asking what’s the magnetic field inside of Jupiter, or at some specific point. Depending on where you look, you find different numbers. From what I found, at the surface of Jupiter it’s 11 to 14 Gauss.
 
The surface of the Sun is just twice what we have here at the surface of the Earth – about 1 Gauss on average. If you want a really strong magnetic field, the best place to look is a sunspot: a specific spot on the surface of the Sun where a magnetic field line is poking through the surface. Within a sunspot you can end up with a thousands of Gauss field. You have very strong fields associated with sunspots.

Fraser: what’s the mechanism that creates those Sunspots?

Pamela: We don’t fully understand these things.

Fraser: Is this that hardest kind of science there is, or hardest kind of space science there is?
 
[laughter]

Pamela: Yeah… this is where you start getting into magnetohydrodynamics. Somewhere inside the Sun, probably at the boundary layer between where heat is transported via radiation (where it just goes from atom to atom to atom toward the surface), to being moved via convection, where you have (large scale) a chunk of hot material rises to the surface (because hot material is less dense) and cold stuff comes down… somewhere in the boundary between the convective region and the radiative region, we think, is where the solar dynamo, the solar magnetic field originates. We’re not entirely sure how this works.
 
Whatever is going on, it doesn’t create a nice, friendly, bar magnet where you have the Sun’s north pole, the Sun’s south pole, and nice, pretty, perfect field lines. Instead, the inside of the Sun ends up creating this tangled web of magnetic fields. Different parts of the Sun are rotating at different rates. This is probably part of the reason the magnetic field lines are so tangled.
 
When parts of these tangled fields twist up and end up coming through the surface of the Sun, you end up with sunspots. So the sunspots are marking the location where a tangled glob of magnetic field is coming up through the surface.

Fraser: How does that turn into a coronal mass ejection then?

Pamela: These tangled bits of magnetic field can actually funnel plasma through them. When the field gets tangled up so tightly that it rearranges itself by breaking and rejoining, that plasma gets shot off into space during the moment where the field lines break and they stop funnelling the plasma.
 
Imagine you have your backyard hose cranked up to full blast, and you make a nice arc out of it, and for some reason you decide you’re going to cut the hose at the centre of the arc. Even if you’ve just turned off the hose, but it’s still filled with the pressure of the water inside, that water is going to blast off in all directions (and get you wet).
 
In this case, we have a hose filled with plasma and when the hose breaks, that plasma gets shot off into space.

Fraser: Doesn’t that plasma still maintain a magnetic field?

Pamela: It’s charges in motion, so it will have a magnetic field, but it’s dominated by other things. Any charge that’s in motion has a magnetic field, it’s all a matter of scaling, however. If I have one lone electron zipping through my room from a cosmic ray, its magnetic field is going to be nothing compared to the magnetic field of my refrigerator magnet, or a coil of wire hooked up to a battery.
 
With the Sun, the magnetic field loops that are creating this coronal mass ejection are significantly stronger than the magnetic field associated with the moving charges inside the plasma. That plasma is really just shooting off from the Sun, heading off in (hopefully) a mostly straight trajectory (or we don’t understand physics) until it interacts with something either gravitationally or magnetically and gets its path changed.

Fraser: All right, so we’ve talked about the solar system; we’ve talked about the Earth, Jupiter and the Sun. Let’s find out – what are some other places where we find magnetic fields out in the Universe?

Pamela: Anywhere you have material moving, you can start looking for magnetic fields. One of the best ways to create a strong magnetic field is to get things moving in loops.

Fraser: One question for you, before that… you say we look for magnetic field – how can we see a magnetic field?

Pamela: (laughing) I was wondering if you were going to ask that.

Fraser: I mean, obviously you can feel it with a magnet, but if the magnetic field you’re looking at is across the Universe, how can you feel it?

Pamela: We look for it in two different ways: the easiest way to look for it isn’t a direct detection of the magnetic field – it’s to look for jets. If you have a magnetic field created by a loop of charged material (and an accretion disk is really nothing more than a whole bunch of loops going together) you can end up with magnetic fields that are perpendicular to the disk and point in and out of the centre of the disk. So we can look for jets: jets are probably a product of a magnetic field.
 
Again, that’s just a sort of a, “it looks and smells like a magnetic field, so we’re going to call it a magnetic field”. The way to directly say, “yes, I know with certainty this is a magnetic field” is to look for effects on how electrons change energies within atoms. We can do this using spectroscopy.
 
If you take the light from something – anything – and you spread it out, you see lines that correspond to places where electrons and atoms have absorbed part of the light of the object. Those lines you see occur in very specific locations where each atom has its own fingerprint of allowed colours at which it absorbs light.
 
The allowed colours, if there’s no magnetic field, have one fingerprint that’s nice and simple. If you induce a magnetic field, the electrons suddenly end up with a slightly different fingerprint, where what might’ve been one energy before might suddenly become three very slightly different lines.
 
So the fingerprint changes. It gets spread out into multiple versions of itself when you induce a magnetic field. The stronger the magnetic field, the more these lines split. This is called Zeeman splitting in some cases. One line becomes three lines and the separation between those lines increases, as the magnetic field gets stronger.
 
Something else we can look for is polarization of the light. Since light has a magnetic field, and an electric field, as part of its characteristics, the light will become polarized as it goes through a sufficiently strong magnetic field, because it will rotate. One way to think of it is we do these weird things with our hands called the “right hand rule” in physics.
 
If you take your (right) hand, and point your thumb and fingers out straight so that everything forms a plane with your palm flat on the table, then your fingers are currently pointing in the direction of motion. If you then bend your fingers in, that is the direction of the electric field. If you point your thumb straight up, that’s the direction of the magnetic field.
 
You can rotate your entire arm, and if we have a whole bunch of light moving toward us and the light is unpolarized, then any of the directions of your thumb and fingers are allowed as long as your arm keeps pointing in the same direction and your palm is pointing along the direction of your arm.
 
If you induce a magnetic field, if you have the light moving through a magnetic field, suddenly everything will rotate so all the thumbs are pointing the same direction (if you have a whole bunch of arms representing a whole bunch of photons) and all of the fingers will rotate so that they’re all pointing in the same direction. When you get all your photons lined up in the exact same way, they’re polarized and we can see that polarisation with our telescopes.
 
Did I lose you?

Fraser: No, no… I understand the technique. We’ve got the jets, we’ve got the polarisation, and we’ve got the changes in the chemical constituency of the light coming from the object. From that, you can try and get a gauge of whether there’s a magnetic field working here and what the strength is.

Pamela: Exactly.

Fraser: See, I paid attention!

Pamela: Okay! Cool – you’re working toward that degree!

Fraser: I had my thumb out, looked like I was hitchhiking…
 
[laughter]
 
Now we kind of understand how scientists look for them. Let’s go back and talk about where are some of the crazy places that we see these magnetic fields

Pamela: In astronomy, we have these things called accretion disks that seem to crop up just about everywhere. When you take a cloud of gas and dust and condense it down to form a star, as it spins, and condenses, part of that disk will flatten out into a pancake and in the centre you end up with your proto-star. That accretion disk can create a magnetic field. The spinning star that is forming can create a magnetic field, and these magnetic fields will couple to each other such that everything’s rotating together.
 
We see these magnetic fields in T Tauri stars. What’s neat is the magnetic field of the T Tauri star can actually lock onto the material and cause it to get dragged out of the accretion disk such that your accretion disk always ends up with a specific sized hole in the centre around the T Tauri star. That hole is created by the magnetic field.
 
This might be a way to explain the fact that hot Jupiters migrate toward the star and stop. That point at which they stop might indicate the point at which the proto-star’s magnetic field had its affect on yanking material out of the accretion disk and created the hole in the accretion disk.

Fraser: I get it, so the hot Jupiter is bumping into particles in the rest of the accretion disk, so it’s slowing down and by slowing down it’s spiralling into the star. Then it hits this empty zone where the star has been so kind as to clear out all the space, and so the planet doesn’t hit anymore friction, so it just stays at that position from that point on.

Pamela: Exactly.

Fraser: That’s cool.

Pamela: It’s very cool. We think there might be similar types of things associated with quasars. These are the disks of material around supermassive black holes where material is coming off of the disk, falling into the supermassive black hole. There’s a magnetic field associated with the accretion disk causing jets out of galaxies (in this case).
 
So before, we just had these little tiny stars in the process of forming. Now we’re talking about entire galaxies that have these disks.
 
We also find these disks around white dwarf stars. So we have stars that are forming have these, stars that have just finished dying have these – accretion disks are a great place to look for magnetic fields.
 
We also find magnetic fields associated with special types of neutron stars called pulsars and magnetars. These are fast-rotating, hot objects. They have ionized atoms in them (these are charged atoms). They’re rotating, we don’t fully understand why they have magnetic fields (this is again, magnetohydrodynamics, very scary, very hard to do), there’s people working on the problem.
 
Pulsars and magnetars have the strongest magnetic fields in the Universe. The Sun has approximately 1 Gauss at its surface. Pulsars have somewhere between 10^12 and 10^14 Gauss fields. These are just huge, extremely strong magnets.
 
Magnetars have 10^15 Gauss fields. These are huge fields – they’re the most magnetic things we know of. If one was nearby, it wouldn’t just rip all of the magnets off every refrigerator on the planet, it would actually rip apart water molecules, because water molecules have different magnetic ends.

Fraser: What causes the magnetic field to get so strong? Wasn’t this once a star like our Sun, with a 1 Gauss field?

Pamela: It all comes down to how fast is the thing rotating. Our Sun rotates about once a month, on average. A pulsar can rotate in some cases, a thousand times a second. The faster a charge is moving, the stronger the magnetic field it creates. The denser you pack together all of these moving particles, the stronger the magnetic field you’re going to get.
 
You can actually do a slight experiment with this if you want to. You can get what’s called magnetic wire at Radio Shack. If you make a bunch of loops of it around a soda can, pull out the soda can and attach the loops to a small battery, you can get a small magnetic field. If you then attach it to a large battery, you can get a large magnetic field. If you attach it to a car battery, you can fling a fridge magnet a couple feet across your desk. It’s kind of cool.

Fraser: I’ll do that right away! That sounds cool! Science we can use!
 
[laughter]
 
You mentioned in the show prep that you wanted to talk about some galaxy clusters. How big can these magnetic fields get?

Pamela: Magnetic fields are actually getting found permeating through all of space. There is work being done to study magnetic fields in galaxy clusters. Here we’re not quite sure what the origins of the field might be. One thing we know for certain is if you take something that’s magnetic and you put a bunch of iron filings near it, the iron filings will line themselves up and become magnetic. You can then bring more magnetic filings in and they’ll become magnetic. You can create these long filaments of magnetic material where you start with just one magnet, and the magnetism gets communicated through the different material.
 
In our Universe, we have these filaments of magnetic field, where we think this might be residual magnetic fields from the early moments of the Universe, that as things have formed, they naturally align themselves along these magnetic filaments. We don’t see the charge and motion, it seems there’s just these natural magnetic filaments left over from some cause that we haven’t fully understood. Things just align themselves along these filaments, and as they align themselves alone the filaments, they continue to maintain these fields.

Fraser: Perhaps there’s some information in the Cosmic Microwave Background Radiation.
 
[laughter]

Pamela: I’m sure people are looking. Everything eventually points to the Cosmic Microwave Background.

Fraser: That’s great. I think if there’s something to take home here, there’s magnetism everywhere.

Pamela: Exactly.