Relativity is used in more day to day situations than you may realize. In this episode, we will count (some of) the ways. This episode is brought to you live from the All-Stars Star Party in Indian Wells, California
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Pamela: Today’s episode of Astronomy cast is sponsored by Magellan TV. Claim your two-month free trial only available at Magellan TV dot com slash astronomy cast. Magellan TV is a brand-new streaming service that features the very best collection of space and science documentaries available anywhere.
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Fraser: Astronomy cast episode 536. Everyday relativity. Welcome to astronomy cast. Your weekly fact-based journey through the cosmos, where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of universe today, and with me, as always, is Dr. Pamela Gay. And I don’t have an introduction in front of me, so you are going to have to say your title.
Pamela: I am Dr. Pamela Gay. I am a senior scientist at the Planetary Science Institute, and the Director of Cosmoquest. And you should all be mapping boulders at bennu dot cosmoquest dot O-R-G.
Fraser: Man. Stop yelling at them.
Pamela: I really need them to map boulders and rocks and craters. Please?
Fraser: So, we are recording this episode live from Indian Wells, California, as part of the all stars party astro tour. We said that this episode of astronomy cast had ended. That we were going on hiatus. That was a lie. This is a bonus surprise. Enjoy. Maybe there will be more things. Who knows? This is going to be a weird summer.
But you missed this one, unless you are here, but then listened afterwards. That is weird. But if you want to come on the next trip, I am going to be going to Iceland in January 2020. So, just go to astrotours dot C-O. They are taking reservations now until the middle of July. So, if you ever wanted to go aurora hunting with me, and also glacier hunting, and also Icelandic troll hunting, you should definitely go to astrotours dot C-O and sign up.
We had a great time last time we went, and it was crazy storms. We didn’t see a lot of auroras, but I think this time it is really going to work. So, astrotours dot C-O, and sign up. All right.
So, relativity is one of the most mind-bending concepts a human can attempt to contemplate. How can different places experience different speeds of time? Well, good news. You are taking advantage of it right now thanks to the handy gadgets like your phone. Pamela, you wanted to talk about some of the super weird ways that we actually incorporate relativity into our lives every single day. But before we get into some of that, let’s just talk about relativity. What is it?
Pamela: It is a set of theories most famously worked on by Einstein. Worked on actually by a whole bunch of people working together. And it describes, literally, our place in space and time relative to one another. And it turns out that even though we are so close, I am not seeing you right now, because it takes the photons of light bouncing off of your body a moment to reach me.
And as I look out further and further, looking at people in successive rows, I am seeing them further and further back in time. And as those photons gravitationally interact with things around the universe, their paths get bent and distorted. And that gravity field, well, there is some weird stuff that happens. Because no matter who you are, no matter how fast you are going relative to something else, all of us see those photons moving at the exact same velocity.
Fraser: All right. So, let me just understand this for a second. So, I am moving – whatever – at 100 kilometers an hour. You’re moving 10,000 kilometers per hour. Someone is moving just a fraction away from the speed of light. And we are all watching a laser beam that has been shot from the International Space Station, and we are all watching that laser beam, and we are measuring the speed of light of that laser beam as it moves through space at the speed of light.
Even though we are all moving different distances. And I mean, I guess, in our everyday experiences, that is not what we experience with, say, a bullet being fired. If you are moving close to the speed of light, and I am moving at 100 kilometers per hour, we see a bullet moving at vastly different speeds.
Pamela: And just in more practical terms, when we are going down the highway, we see the cars that were passing moving relative to us at ten or fifteen miles per hour, unless you are a crazy person. But if you are standing on the side of the road, you see those cars going 60 to 90 miles per hour.
And this difference in how we perceive velocities of cars, velocities of runners relative to our own motion, is not true with light. No matter who or what you are, light is going 300 kilometers per second, and that is the law.
Fraser: Right. So, this is, of course, the amazing discovery that Einstein made, and I am sure that someone could have thought of it earlier, because it is so weird, right? That time is the thing that changes.
Pamela: This episode is brought to you by Bark Box. For a free extra month of Bark Box, visit W-W-W dot Bark Box dot com slash astronomy. When you subscribe to a six- or twelve-month plan. As a lot of you know, I’ve got two dogs; Eddie and Stella. Eddie was my reason for getting Bark Box, and month after month he devoured the two large treats, played with the themed toys, and I would train him with the other made in America and in Canada tasty, healthy goodness that came packaged in every box.
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Fraser: So, fine. And it is not like this hasn’t been proven a million times. Einstein is still right. So, then, what are the practical applications. How do we actually experience this? Are we experiencing time dilation as we are moving around in regular life?
Pamela: Yes. And where is starts to matter is once upon a time, we were worried about whether our pocket watches were closely enough aligned to keep the timetables of the trains in Europe.
But nowadays, when we are trying to get a satellite hook up to bring two news stations across the world together, we need to sync up those radio waves so that something that has a millimeter wavelength lines up on the other side of the world. And this requires more accuracy than your pocket watch is going to have.
Pamela: And as we work out all these timings, we have to take into account the fact that where we are on the surface of the earth, we are experiencing a whole lot more gravity than the space signals are going off of. And this creates one sort of shifting light and shifting time.
Those spacecrafts are moving at a different rate around the earth’s center than we are as the earth rotates. That creates another expansion of time.
Fraser: Okay. So, hold on. Those are two separate issues that maybe we should break up, right? So, there are two factors that will impact the amount of time that you experience. Gravity wells, and velocities. Can you explain that?
Pamela: So, with a gravity well, gravity is going I shall hold on to you. And the light, as it tries to get away, actually gets red shifted. As you look into a black hole, you see things getting redder and redder as it falls in. And part of this is doppler shifting, and red shifting, but gravity is also playing a role.
As you pull out of the gravity well, that pull gets less, and light is getting affected less. Time is getting affected less. And so you have a difference due strictly to how far you are from the center of mass, and how fast your clock is ticking.
Fraser: Right. And the practical application for this – if you want a way to sort of think about it is think about the movie Interstellar, because they gave us this example. Spend some time near a supermassive black hole. Spend an hour, and you come back, and it has been 40 years for the people that you left back at home. And so, we, down here, on planet Earth, are experiencing less time than people who are out in space.
Pamela: If they are stationary.
Fraser: If they are not moving. Yeah. They are stationary. Yeah. Yeah. People who are out in space, relative to us. They are not moving, but they are just out there in space. They experience – woah. So, do we see them moving in slow motion? Do they see us moving in slow motion?
Pamela: They would see us moving in slow motion, but the catch is, you would fall out of orbit if you tried to do this. It would be very messy. Don’t do this.
Fraser: Right. So, just before they plummet to their death, they notice that we are moving ever so slightly a little slowly. That is weird, and then the screaming, and then the burning.
Pamela: And the death.
Fraser: Yeah. Okay. So, that is the one half of it, and then the other half of it is the velocity.
Pamela: And this is that twin paradox that they played with, with Scott and Mark, the two twin astronauts whereas Scott went around and around the earth, his velocity – he was accelerated to a higher rate of motion. And you look to see who did the acceleration to figure out whose time was shifted. You look to see who was accelerated. Scott was accelerated.
If he wasn’t, he would still be on the planet. This experiment wouldn’t have worked. He went at the higher velocity, and because he was moving faster, in order for him to see light traveling at the same rate, his clock has to slow down. The way I remember this is he was Buck Rogers in the 21st century but didn’t quite get there because he wasn’t going fast enough. Buck’s time slowed down, thus he made it.
Pamela: So, the person who is on orbit, their clock slows down, they visit the future.
Fraser: So, then, is there some perfect balance point where – because the astronauts are moving at 28,000 kilometers per second. That is way faster than us. So, they are experiencing – so, we would see them moving in slow motion, but they are outside of our gravity well, and so then, they would see us moving in slow motion. So, is there some point where they balance out?
Pamela: Yes, but not with the earth, because we would fall out of orbit. If you go to something that has a greater mass, you can find that balancing point where the gravitational red shifting, and the time due to your velocity and acceleration, where those two counteract each other. Just not here, do that. There, we can’t get there yet, so maybe don’t do the experiment.
Fraser: Right. Right. And I know that when we look out to the other side of the entire universe – the very edge of the observable universe, that is as far as things can go. And those places have actually experienced 30,000 years of time different to us because they are moving away from each other. Like, time has no meaning.
Pamela: No. It doesn’t.
Fraser: Yeah. All right. So, then now your head is like come on. Prove it Fraser and Pamela. Fine. We are going to prove it. What are some of the practical applications how relativity has moved into our lives every day?
Fraser: Pokemon. I got to catch them all, but they are moving in slow motion.
Pamela: We are here when we could be out for the adventure day. And we are both Pokemon Go players.
Fraser: You are, like, a serious Pokemon guru. I mean, I dabble. You are hardcore.
Pamela: Right. I am.
Fraser: So, fine. Why could I not play Pokemon Go?
Pamela: No. Well, you could, but it wouldn’t know where you are, and you couldn’t catch them all.
Fraser: Right. You’ve got to grab that Pokestop right now.
Pamela: I’m totally spinning – I got a gift. I will send you a gift.
Fraser: Will you send it to me? Okay. Great.
Pamela: Yeah. Yeah. On wizards unite, I play that as well. I – Nayak, you are a problem in my life. So, these things that we do with augmented reality that paint our world with games, with information that rely on few meter accuracy and our position on the planet, all of these things have to take into account that we are latching on to three to five satellites that are high above our heads.
And if we weren’t latching onto those satellites, we wouldn’t have this accuracy. But those satellites are moving. And so, we have to do the relativistic corrections to the times, or we would be misplaced in time and space, and all of these things that are fun, informational, and prevent us from getting lost – Google maps. Thank you.
Fraser: Okay. So then, how does that work then? So, your phone knows what time it is? And how does relativity affect your phone?
Pamela: So, you latch on to three different satellites – or five – three to five satellites to get your position. If it is only two, you don’t know where you are. Your phone, your watch, whatever it is latches on to three different satellites that are zipping in slightly different directions, all have different light travel times to reach your phone, and your phone listens to the time the satellite sent the signal, compares the times for the three different signals, looks to see where the satellites thought they were when they sent the signal, does a relativistic correction.
Using that relativistic correction, it goes the satellites, when they sent this signal, were actually these three places. I now know my separation to three different points, and with three points, you can figure out where you are in x, y, and z. Left, right, up, and down. So, you are literally drawing three measuring sticks between satellites and using relativistic corrections.
Fraser: Okay. So, your phone –
Fraser: Your phone detects satellite one is moving towards you, and goes oh, you are moving towards me. So, time, you are moving in slow motion. Therefore, the time that you think you are sending the signal in not the time that I’m actually receiving the signal. I’m going to make an adjustment. But then that other satellite that is over there, that is moving perpendicular to me, is experiencing a different thing, and ultimately you are out of the gravity well, to a certain extent.
And it is calculating the velocities of all of these different – and the positions, and the directions it is going, and then it is accounting for that. And so, then, if you didn’t take Einstein’s equations into calculating your position on Earth, would GPS work at all?
Pamela: No. Not really. I mean, it would roughly tell you where you are.
Fraser: You’re on Earth.
Pamela: Yeah. And let’s not try. We know, because of Pokemon Go, relativistic equations make our lives at least a little more, well, wiggly.
Fraser: All right. Okay. So, fine. So, our phones, literally – I mean, for those of us who aren’t playing Pokemon Go – those of us who depend on, say, turn by turn driving directions, or hiking into the forest, again, you need your GPS to be accurate.
Pamela: Oh, yeah. Yeah. Yeah.
Fraser: Yeah. So, again, it is so funny. Like, you have a conversation with someone who is like I don’t believe Einstein. Like, fine. Then, throw away your phone. Give me your phone, actually, doesn’t believe in Einstein. I will take your phone, please. And we’ll go from there. All right. So, what else?
Fraser: Explain how.
Pamela: This is one of my favorites. So, if you’ve ever looked at the models they have of the lunar landers, there are a whole lot of shiny gold on that stuff. And this is fairly thin, fairly pure actual gold. And as it is sitting there, hanging out, going I am scattering mostly yellow light.
The reason that we see it the color that we see it, and part of the reason that it makes such a fabulous radioactive particle deterrent is that you have this extraordinarily dense atomic core, and this extraordinarily dense atomic core means that the photons that it interacts with, it preferentially shifts their colors as they interact down in the core, and we end up with less UV and blue light then we would if it didn’t have this dense core. And thus, more yellowy gold than we would without relativity.
Fraser: But how is it due to relativity?
Pamela: So, one of the awesome things about relativity is it talks about how light gets bent in these high density situations, and then you start getting into these affects of as you get in so close, everything is so dense that the physics goes out of norm. And if you try to use Newtonian physics to describe the motion, Newtonian is like no. Just, no.
I am going to misplace those photons and change the color. But with relativity, you can start to figure out how the momentum is changed of the photon. How the length has changed over the photon. All of these factors together, and gold, unless it has a lot of impurities, is going to give you a yellow refection.
Fraser: But I mean, it is not just gold, right? It is going to be any heavy element pounded into a thin film that has a lot of protons down thee in the core, right?
Pamela: And it gets even weirder when you start looking at things like Mercury. Mercury flows like a liquid, reflects like a mirror. And the way that it is able to do all of this is it was due to its super high-density core again. And so, with Mercury, again, super high-density core, super weird physics, super awesome material. So, anytime you broke a thermometer, and your teacher didn’t’ catch you fast enough, you played with the mercury?
You were playing with relativity. You can say you experienced it while also experiencing a toxic substance. Don’t play with Mercury.
Fraser: Right. Right. But like, I’m just trying to imagine what the density of the material impacts the relativity, and the –
Pamela: So, think about a black hole is a high-density thing. It changes the physics we work with.
Fraser: Right. But isn’t that from the mass? Or is it from the density? Or, is that the same thing?
Pamela: Well, it is in many ways the same thing. You can have a star with ten solar masses of material, but it is not a black hole because the density is not such that you can get close enough to the sun. Yeah.
Fraser: Right. Right. Okay. I see. I see. So, it is the density that is actually doing the heavy lifting.
Pamela: And there are other places that I did not realize that we have to make relativistic corrections until I started doing research to prep for this show. And one of those things that I made in school was an electromagnet. You wrap a whole bunch of wire around your fingers. You use your other hand to attach the wires to the battery.
You don’t really shock yourself. Some of the electricity goes through your hand. Most of the electricity hopefully goes through the wire. And you can drag things around on the surface of your desk.
Fraser: With you hand?
Fraser: Wait. Wait. Wait. Wait. Wait. You can – I’ve never done this. Like, I’ve coiled it around with a nail. Yeah. You take a nail, and you coil a copper wire around the nail, and then you attach the two sides to a battery, and you create an electromagnet. Congratulations. There is your science fair project. But you say you can do this with your hand? With your finger?
Pamela: So, you – it is just like you are winding up yarn, or cables, or something. You wrap the wire around your fingers. You have a loop of wire. You pull the loop of wire off of your fingers. You don’t keep the loop of wire on your fingers. You then grab a battery and hold the two ends of the wire on the battery. If you were in a cheap school, like the one I went to, and you don’t have battery cases, and you have an electromagnet, you don’t require the nail to make the electromagnet. You require the coils of wire.
Fraser: So, are you like a meat magnet?
Pamela: Yes. Yes.
Fraser: Neat. A magnet made of meat. All right. So, fine. Magnets. We are talking about electromagnets.
Pamela: We are talking about electromagnets.
Fraser: I’m intrigued.
Pamela: Now, if you have current running through a wire, moving charge generates a magnetic field. And if you have two wires next to each other, that have current – my arms can’t do that, for the people who are watching – if you have current with flowing in opposite directions in two parallel wires. You can get those wires to attract each other. You can get those wires to repel each other. And to really figure out how much of this is going on, you have to do relativistic equations.
Now, when we teach this to freshman in university, we leave those corrections out, because in the grand scheme of all the friction and everything else your standard electrical engineer is going to have to deal with, these are not a problem. But as we get into building faster and faster electronics, with more and more delicate wires – a super delicate wire that is getting yanked on by electromagnetism, well, you can wreck your circuit. So, you have to start worrying about these detailed effects.
Fraser: Right. But that was the force. Like, there was definitely a force that is applied to a wire, and same thing. You have a wire and you apply electricity through the wire, and it goes through the coil, and it will yank like a magnet. But I don’t understand where the relativity of this comes in. Is it that the –
Pamela: Electrons are moving close to the speed of light.
Fraser: Right. Okay. So, we’ve got something that is moving close to the speed of light, and you’ve got things going various directions in a computer at close to the speed of light. And in different, and in some cases moving from one spot to another spot, and when they move really close together, when you are looking at just a nanometer apart, they are interfering with each other, and experiencing time dilation and relativity.
Pamela: And it is in figuring out how strong the magnetic field is that you have to start to look at how fast the charge is moving. Any of us, if we are really bored, can put a natural magnet inside a coil, and reverse this experiment and generate electricity by shaking a tube with a magnet in it that goes through the wires. I am not going to do the hand gesture for that. And this generates current.
Now, we are not moving the magnet that fast. The faster we move the magnet, though, the more current is created. The faster the current moves, the more magnetism is created. As we get current flowing faster, you have to take into account relativistic effects.
Fraser: So, would like really advanced – modern computers, they are taking that into account, right?
Fraser: And they are running at whatever clock rate that they are – the heartbeat of the computer – as it is performing it’s instructions, it is taking into account the relativistic accounts of all of those electron moving around inside the computer to make sure that as it is sending out instructions, and instructions are coming back with the answers, it needs to account for the time dilation for this.
Pamela: The manufacturers do all of that when they are building it.
Fraser: Yes. Of course. Of course.
Pamela: And then it is out of mine.
Fraser: Yeah. No. You don’t specifically have to deal with it.
Pamela: My processor isn’t worried about that. And it also becomes a problem when you are worrying about super conductors. And the faster we get things going, the faster we get our information from point a to point b, the more we have to worry about the corrections we need to make to what happened in the process of getting from point a to point b.
Fraser: That is amazing.
Pamela: And just in general, when you are firing an electron around, that electron is like hi. I’m going fast. Relativity matters. And old CRT televisions, they were firing electrons at the surface of that cathode. So, you have a ray of electrons –
Fraser: A beam.
Pamela: – going through a tube to hit a cathoid, otherwise known as a cat’s electric table – a heated table as far as I can tell – a cat. Cats like to sleep on CRT’s. Modern cats don’t have as much luck, and this is why they claim our keyboards.
Fraser: Right. Right. But so, like, an old television, you’ve got an electron beam. You’re one step away from your own large hadron collider there. You’ve got a particle accelerator in your house firing a beam of electrons in your general direction to entertain you.
Pamela: Yes. Getting stopped by that screen.
Fraser: By that screen. But you’ve got something that is moving at some dramatic percentage of the speed of light, and so you are going to have to take into account relativity.
Pamela: Especially when you are literally painting the screen with that beam using the magnets inside to direct the beam to vary the intensity so that you see different amounts of light, and different colors getting triggered in different places on your screen.
Fraser: I kind of imagine a cathode ray emitter is firing off these electrons, but it is accounting for the time dilation that each one of these particles is going to be receiving to make sure that it all comes together for us at exactly the right time. And if it didn’t make those kinds of modifications to the timing, television would suck.
Pamela: Yeah. And it all ended up in how they shaped the magnets was dictated by relativity. So, if, like me, you have an old cathode ray television in your basement because the garbage man won’t take it. And Goodwill won’t take it. And no one will take it.
Take it apart and look at the magnets. Look at the cathode ray. And the recent ones aren’t as fun as the ones that might be in grandparents’ basements or attics. But these were electrons going at 30% of the speed of light. And it matters.
Fraser: All right. Awesome.
Pamela: And other than that, we just have to look at things like the sun.
Fraser: Mm-hmm. Right. And we know that the sun is eight and a bit – eight minutes and 20 seconds away, or something like that. So, we are seeing the sun as it was eight minutes ago. That is fine.
Pamela: But more importantly, if relativity didn’t work, nuclear reactions wouldn’t work. Our sun would not have a power source.
Fraser: Right. Right. Fusion.
Pamela: And without a star, we would probably be dead.
Fraser: Okay. Fine. Right. But I will give you that. I appreciate my existence. Thanks sun. I apologize for all of the things I’ve said about you in the past. Your terrible heat. It’s okay. Okay. Fine. But how does fusion require relativity.
Pamela: This is the look of where do I start? That required ten years of university.
Fraser: Also, you’ve got three minutes.
Pamela: Yeah. That too. So, ah. Collisions of particles rely on relativity to dictate how things tunnel from a to b. Lower the energy barriers and allow the things that aren’t dictated by quantum mechanics to work. If it is not quantum mechanics, it is relativity that basically describes the sun.
Fraser: Perfect. I feel like I just got my degree. Ha ha. In your face education. All right. I think we’ve reached the end of the time we have here today. So, I think the point here that we should all really take away is thanks to Einstein. You were right again. And thanks to relativity, every day our lives are made better by the mind-bending concept of relativity.
Pamela: Go catch those pokemon and thank your GPS.
Fraser: Yeah. Nobel prize winning concept to help you catch pokemons. Did you have any names with you, or should we just generally thank all of our patrons? Thank you so much for this bonus thing.
Pamela: Yeah. So, I don’t have any names with me right now to read out. Now, we are going on hiatus. This doesn’t mean the work stops. We are going to be working to plan out our next year. Suzy is spending the summer going through and cleaning up our website, setting everything up.
And to thank all of you for kicking around, we are probably going to be sticking lots of bonus randomness into the feed, and we will be returning as we always do with dragoncon, and whatever Fraser is doing come September. It is changing for the summer, but we are not going away, and we would not be able to do what we do without all of the people who support us on Patreon dot com slash astronomy cast. You allow us to pay Suzy a livable wage for everything that she does.
Fraser: Thanks Suzy.
Pamela: Thank you Suzy. And she puts up with so much from the two of us. And thank you. I just kind of don’t know what to say.
Fraser: All right. Yeah. And we will see you on the – maybe not until September. Or maybe, surprise, something else will happen.
Fraser: All right. Thanks everybody.
Pamela: Bye bye.
Suzy: Thank you for listening to astronomy cast, a non-profit resource provided by the Planetary Science Institute, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomy cast. You can email us at info at astronomy cast dot com. Tweet us at astronomy cast, like us on Facebook, and watch us on Youtube. We record our show live on Youtube every Friday at 3:00 PM eastern, 12:00 PM pacific, or 19:00 UTC. Our intro music was provided by David Joseph Wesley. The outro music is by Travis Surl. And the show was edited by Suzy Murph.
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Duration: 36 minutes