If there was enough mass to cause a big crunch, would inflation go backwards too? How do spacecraft know that hydrogen is bonded to water? And why can’t we see everything that’s ever fallen into a black hole?
If you’ve got a question for the Astronomy Cast team, please email it in to firstname.lastname@example.org and we’ll try to tackle it for a future show. Please include your location and a way to pronounce your name.
If there was enough mass to cause a Big Crunch, would inflation go backwards, too?
- Inflation Theory — WMAP
- The Big Crunch
- BAUT Forum Discussion of what could be beyond our Universe
- Inflation Theory Takes a Little Kick in the Pants — Universe Today
How do spacecraft orbiting Mars know that the hydrogen they detect is bonded to water?
- How gamma ray spectrometers work –– Mars Odyssey
- Evidence of Vast Quantities of Water Ice on Mars — Universe Today
- Abstract: Constraints on the Distribution of Hydrogen in the Polar Regions of Mars and Implications for Ice Formation processes
Why can’t we see everything that has fallen into a black hole?
- Anatomy of a Black Hole — UIUC
- Event Horizon
- Gravitational Redshift
- Maximizing Survival Time Inside the Event Horizon of a Black Hole — Universe Today
Can an object the size of the Pistol Star be so big that it stops up a black hole?
- Pistol Star — HubbleSite
- Angular Momentum
- Video of Neil de Grasse Tyson discussing black holes and spaghetification
Does the vacuum of space have an odor?
- ISS Astronaut Don Pettit’s Journal about the smell of space (he describes it as a “sweet metallic odor”
- PAHs (Polycyclic Aromatic Hydrocarbons)
- Other “stinky molecules in space:” methane, formaldehyde
- Video: Methane In Space — Discovery.com
Can white holes turn into black holes and vice versa?
Does the Universe go on forever, or does it wrap back onto itself?
- Is the Universe Infinite? — WMAP
- Study Hints Universe is Finite — Nat Geo
- Episode 81: Questions on the Size, Shape and Center of the Universe
- Episode 78: What is the Shape of the Universe
- Episode 79: What is the Size of the Universe
When will the four gas giant planets be in a straight line (plus Eris and Sedna)?
Why can’t the human eye see the entire electromagnetic spectrum?
Transcript: Undoing Inflation, Searching for Water, and Seeing Everything a Black Hole’s Ever Eaten
Fraser Cain: Time for more questions.
Dr. Pamela Gay: Let’s hope they’re not as scary and hard as last week.
Fraser: I don’t know if that is possible [Laughter] because like I said, I sort of saved up a whole lot of duzys in that and unleashed them on you in one show. I think this is sort of a regular mix of hard ones and really hard ones.
If there was enough mass to cause a big crunch, would inflation go backwards too? How do spacecraft know that hydrogen is bonded to water when they detect it? Why can’t we see everything that has ever fallen into a black hole?
Let’s get on with the first question.from Richmond, Virginia asks: “If the mass of the universe were sufficient to cause a big crunch, would only the matter of the universe be pulled back in or would the fabric of space also be back in? In other words would inflation be undone?”
Alright let’s see, the universe is expanding but there was the thought that astronomers weren’t sure that the expansion of the universe would go on forever that there was enough mass in the universe that it was kind of like a car coasting to a stop up a hill. The car sort of would roll back down the hill backwards. That is what would happen.
The gravity of the universe would pull everything together back into something called the ‘Big Crunch’ which would be like a reverse big bang. I guess the current thinking now is thanks to dark energy the universe is going to expand forever and even accelerate.
I guess the question then is if the universe did have the mass to pull itself back in would it completely do the opposite of the big bang or would it be different?
Pamela: This is actually just another way of asking the question what’s beyond the edge of space – mass stuff.
Fraser: It is?
Pamela: Yeah because our universe is in many ways defined by the space it fills. We have in the inflation area; it inflated all of the whole spatial grid work that we put the mass on.
If the universe collapses back in on itself and everything comes back down to a point, we can’t really talk about what’s outside of that anymore than we can talk about what is the universe expanding in to.
There is just not a way for us to get at that mathematically or linguistically. It’s not defined. This is sort of like the divide by zero problem where you get excel yelling at you.
If the space grid that the mass is hanging on collapses down we can’t really define what’s outside of it.
Fraser: But I guess that’s the question, would the contraction include the mass? Wouldn’t it kind of like be the big bang created I don’t know, the tablecloth with all of the dishes on it.
But the big crunch would be you taking all the dishes and crunching them back down together but you’ll still be left with the tablecloth.
Pamela: It actually carries the tablecloth back in with it. This is more of the case of you blow up a bubble with bubblegum and then you suck the air back out of it.
With our universe we can’t talk about what’s outside of the bubblegum and if we suck the bubblegum back down into our mouth we can’t talk about where the bubblegum used to be. We don’t have language for that.
Fraser: The mass and the fabric of space itself are intertwined. You can’t have one without the other.
Pamela: Right and it’s the whole fabric of space that gets crunched back down in that original scenario.
Fraser: The universe would be entirely crushed down then. I guess the question then is would you get a reverse inflation?
Inflation was that moment where the expansion of the universe was much, much faster. Would you get that in reverse as well?
Pamela: Here we just don’t know. Inflation is something that we’re still struggling to find ways to understand. It was this period of time where everything expanded exponentially for the briefest instant. Because of that everything got smoothed out and we were able to end up with the universe we have.
If we hadn’t had the inflation we would have definitely crunched back down in on ourselves. We don’t understand it real well. We don’t know what force caused it.
We just have ideas that are being chased by some of the smartest people in the world. The idea of running it backwards, well we don’t know. I’m sure that there are theorists out there that have thought very hard about this but it’s something that until we understand what originally caused inflation it’s hard to figure out if you can run it in the opposite direction.
There’s also the as everything crunches back together you have to worry about things like black holes getting generated in wild ways, what sorts of bottle-necking affects are you going to have. It is a very different situation and we just can’t quite get there from here.
Fraser: I guess it’s purely theoretical because our current understanding is that the big crunch will never come.
Pamela: Yes, we’ve been saved. Dark energy is really good for at least this one thing we’re not going to crunch in on ourselves.
Fraser: Joshua Morrison from San Jose, California asks: “I understand that spectrometers on spacecraft orbiting Mars look for water by searching for hydrogen. How do we know that the hydrogen that they find is bound up in water and not some other molecule like methane?”
Is that true? Is that how spacecraft look for water? They look for hydrogen?
Pamela: It’s a little bit more complicated than that but basically there are gamma ray spectrometers that we use when we’re looking for different elements on the surfaces of planets. When cosmic rays, high energy rays from the surface of the sun hit the surfaces of the planets they can as they go through the surface interact with different atoms and molecules and send off neutrons.
Through this process eventually another high energy particle ends up being released and that can be measured by the gamma ray spectrometer. Depending on the energy that is captured we can say what it was that it probably originated out of.
We’re able to look for things like potassium and hydrogen all through these different gamma ray spectrometers. When it comes to figuring out what exactly that hydrogen might have belonged to ahead of time this is where we have to sort of think about what we already know about where the data is coming from.
You have cosmic ray coming in and it doesn’t make it that deep into the surface of the planet. We know what the temperature is. We know roughly what the pressure is. We know the physical characteristics of the area within those first couple meters of the surface where the cosmic ray has penetrated and caused a gamma ray to go flying off.
So we start thinking about what things exist in that area that might have hydrogen associated with them. The thing that is most likely and that we’re pretty sure that we’ve found is frozen water beneath the surface. Methane for instance doesn’t like to exist at those pressures and temperatures.
It is a matter of what is the chemistry, what is the most highly likely thing. Now we could be completely wrong. We could go down, dig two meters into the surface of Mars and discover that it is some overly rich hydrogen rich mineral no one had ever expected but that’s highly unlikely.
Because we know basically how planetary chemistry works we know what is most likely and so in this case we’re pretty sure when we see potassium creating gamma rays it is one thing. When we see hydrogen creating gamma rays it is water. We use our knowledge of chemistry to get at there is likely water because we see gamma rays off of hydrogen.
Fraser: Seeing the hydrogen doesn’t tell us that it is water. It is that matched with our understanding of chemistry and predicting what we would find in those various locations. I guess as you say we might find something completely unexpected but that’s probably not the case.
Pamela: One of the other things is if you look at one of the maps of where we think we’re finding water we can look at the surface of the planet and see ice. This is the highest levels of water that we are detecting are in the northern and southern regions where there are polar ices.
There is reason to believe that we’re right. We’re also able to find through other means the presence on the surface of minerals that can only be formed when water is present. We have lots of different lines of evidence other than just gamma rays coming off of hydrogen atoms.
Fraser: Right but that really helped to map it very specifically.
Fraser: Chad Carlock from Davis, California asks: “Why can’t we see everything that has ever fallen into a black hole right there right outside the event horizon forever falling in but never actually doing it?”
What? [Laughter] Well, why would we?
Pamela: Well it is actually not that crazy a question. As far as an outside observer can tell the closer to the speed of light something is going the slower time is going for the people experiencing it.
If I had the capability of watching someone zip by me at near the speed of light they would appear to not be moving at all because time for them would have slowed down relative to time for me.
For someone starting to get really close to the event horizon and pass through the event horizon of a black hole time is basically stopping. In the mathematics of it nothing ever quite crosses that surface it just sort of gets stuck there as time stops.
Fraser: Does it actually get stuck there or just from our prospective outside the black hole?
Pamela: From our perspective outside the black hole to the poor slob that made the mistake of getting too close and is on his way to his death if he’s not already dead, time is chugging along just fine and things aren’t looking so good for him.
Fraser: That just gives you a headache to think about. [Laughter] You fall into the black hole and you die really quickly from your point of view.
But I from outside the black hole watch you fall into the black hole and you kind of linger there for the age of the universe.
Pamela: It’s one of those really depressing things. The nice thing is that due to this thing called gravitational red shift and the resulting power as well, we don’t actually have to watch the suffering.
As you get closer and closer to a really massive object light that you’re radiating trying to get away from you and that object has to basically climb uphill. It has to climb out of that gravity well.
In the process the wavelength of the light gets stretched and stretched fading toward the red, toward the infrared, through all the wavelengths we’ve been discussing in recent shows. What we would actually perceive is the person fading away into really red wavelengths and then eventually just fading away as they sink into the gravity well of the black hole.
Fraser: Would they be fading away like into infrared and into a submillimeter and then eventually just into radio waves?
Pamela: Yeah, exactly. The nice thing is though there are no black holes nearby enough that we could watch this sort of process. At the same time the really bad thing is there are no black holes near enough by that we can watch this process. It is a Catch 22.
Fraser: Right, we don’t have to worry about it happening and we can’t see it happen. I’ve wondered though if you held a stopwatch and you actually clicked your stopwatch at the time that you were finally consumed [Laughter]what time would that be in the universe? Would that have taken trillions of years from the outsider’s point of view?
Pamela: This is one of those things that I’ve heard people whose primary research is on relativity get into. There are a lot of subtleties involved. I have to admit it is one of these things where one theorist will be saying it never happens and the other one is throwing out exceptions and I simply go we can’t watch so I’m going to move on with life.
Fraser: I remember doing an article I think it was put together by Lawrence Krauss was the original research with it just being that the black holes can never form because of this relativistic problem. That the only true black holes would have had to have formed during the big bang.
Fraser: And that any black holes since then are still forming and won’t actually form because of this relativistic problem that because of the time dilation the mass doesn’t get into it before the end of the universe.
Pamela: But clearly we do have black holes that look, act, smell and behave like black holes and so there is this contradiction between theory, reality of black hole in the center of the Milky Way we can observe the sucker.
Fraser: No, I think the point was that it red shifts so far that the wavelengths are almost infinitely long. It still hasn’t completely from our vantage point, finished. The mass isn’t in and done and shut up. That’s all.
I know it is a point of controversy and it definitely hasn’t been decided by the theorists or the observational astronomers [Laughter] so we’re going to move on.
Jonathan Gore asks: “Can an object the size of the pistol star be so big that it stops up a black hole?”
For those who don’t know, the pistol star is thought to be one of the largest stars in the universe which is kind of at the theoretical limits of star size. It think it is 2,000ish times the diameter of the sun it would extend out.
Pamela: It has massive solar winds. It is blowing off the outer levels of its atmosphere.
Fraser: Yeah, more than a hundred times the mass of the sun. Crazy star, so the question is then could a black hole just gobble that up?
Pamela: It depends on the angle of impact. This is one of the crazy things that we have to worry about in astronomy. Angular momentum has this terrible habit of mucking up everything we want to do.
If you were able to using some alien space drive take the pistol star and hurl it at a black hole or hurl a black hole at it, it really doesn’t matter what direction the vectors are pointing but do it such that the center of mass of the black hole and the center of mass of the pistol star collide on a straight line, you could just hurl it straight in and life would be good.
Easily gobbled you now have a bigger black hole barring the whole how long it takes to fall in and it never quite gets in space time problem that we just discussed knowing that.
If instead you had the pistol star so that it goes in at an angle which is really a much more likely scenario, then it is going to actually end up spiraling into the black hole. As it gets shredded, as it gets spaghettified. As it gets torn apart it has to shed the angular momentum that it has from the orbit, shed that energy and fall into the black hole.
You can get a bottleneck in the process of trying to shed all of that angular momentum and fall in. Eventually it will be consumed. It will just take it a little while.
Fraser: Right and that’s the energy that we see being given off from super massive black holes. This is too much material trying to clog up the drain. It is going to get in there, just give it some time.
That’s why the black holes go through the active and then a more quiescent phase because sometimes they’re just too greedy, too much material and they can’t [Laughter] eat it all like the pistol star or a thousand times the mass of a star like that. At other times it is quiet, hasn’t had a meal in a million years.
Pamela: What’s really cool is when you start throwing at super massive black holes in the center of galaxies not just one pistol star but a few thousand of them you get basically quasars.
Fraser: Don’t worry though the black hole will get around to all of them. It will always clean its plate.
Pamela: In the process this material that is falling in, this disc of material will reach sufficient densities and pressures and temperatures that it is able to undergo nuclear reactions like a star but it is this big pancake of material. I just love that.
Fraser: That’s pretty cool. You get the conditions of a star just because mass is being you know mushed up by the black hole but it is no real star.
Pamela: Right and you can get this with regular novae as well where you have material falling into thedisc around a white dwarf or a neutron star as well. It’s not just the super massive black holes. It is just the scale of what is going on in the super massive black holes that is so cool.
Fraser: Ann Durham from Indianapolis, Indiana asks: “Does the vacuum of space actually have an odor?”
What? Okay so if I stick my head out of the spaceship with no spacesuit on and take a sniff, that’s not going to work is it?
Pamela: No it would be rather devastating to your poor innocent sinus cavities. The thing is I understand why she is asking this question. It is because we keep talking about finding things that are stinky like methane and formaldehyde and polycyclic aromatic hydrocarbons. All these really complex stinky molecules exist out in space.
There are just not that many of them. What you can say is were you able to go out and scoop up a bunch of these different molecules, pull them into your spacecraft with you, siphon out all the ones that would kill you and take a good whiff, yeah space is stinky. It is filled with stinky stuff.
Fraser: I know that the astronauts when they went to the moon said that the lunar dust created a smell that they were able to recognize. I guess it just depends on what you’re encountering. Space itself, especially the vacuum of space, that’s nothing, right?
Fraser: There are no molecules in there; nothing to interact with your nose.
Pamela: It is the random molecules that exist that – yeah, vacuum of space, nothing. It will kill you.
Fraser: Peter Gilmore asks: “Can white holes turn in to black holes and visa versa?”
So, black holes we know what that is. White hole is this theoretical object that what?
Pamela: The idea is that you can have a perfectly empty space that during the big bang ended up with the properties mathematically of a black hole but they don’t actually exist because the second any matter or energy (because they’re really the same thing) falls into a white hole it ceases to exist.
Fraser: Now ceases to exist or turns into a black hole?
Pamela: Ceases to exist.
Fraser: So one little photon in your mathematical structure and it just goes pop.
Pamela: Right it’s not going to happen, we’re so sorry. A white hole is a function of mathematics but to exist you have to have perfect vacuum. Without the perfect vacuum you’re stuck and any little bit and it goes away.
Fraser: I think to analogize can a balloon turn into a pile of needles, right? [Laughter] You know, you take your first needle, poke it into your balloon and that’s as far as you get. The balloon pops, you got your first needle and then you’re going to bring more needles over there but the balloon is already gone.
You can’t kind of go through the intervening step I guess so if you did have a white hole, the first photon hitting it would collapse it and then it would be gone.
Theoretically you could later on locate a black hole in the same place where the white hole was but it wouldn’t be that one turned into the other.
Fraser: Sorry Peter you’re going to have to come up with some other mad scheme to destroy the universe. The next question comes from Brad Goodspeed from Toronto, Ontario: “I’ve noticed on the show that when Pamela refers to the possibility of the universe being infinite she always adds the condition that it would therefore wrap back onto itself. If you could look far enough you would be able to see the back of your own head. Isn’t that just another way of calling the universe finite? What is the problem scientists have with a universe that goes on forever and ever with no end to the amount of matter within it?”
Is that true, is that what you say? I don’t think that’s true.
Pamela: I hope that’s not what I say. Now I have this terrible urge to go through and very carefully read all of our transcripts.
If the universe is finite then it wraps in on itself? It is if it is infinite yes then things can go on forever so Brad is right. The universe could totally be infinite in which case you fire two laser beams they go off forever hopefully staying parallel to one another forever and never coming back to where they started.
If the universe is instead finite because we have this geometry where lines stay parallel to each other forever, in that finite case those rays should come back to their starting point. That’s just kind of cool.
Fraser: For more information listen to our three part episodes, “What is the Size of the Universe?” “What is the Shape of the Universe?” And I think “Where is the Center of the Universe?” We cover all of that.
How big is the universe? We kind of covered that sort of what does it mean for the universe to be infinite versus finite and what shape is it and so on. We do cover that.
Pamela: What’s kind of cool is the fact that a finite universe would cause light rays to come back on itself. We can put limits on how big the universe is just by looking at the cosmic microwave background, so all good information does indeed come from the cosmic microwave background.
Fraser:asks: “When will the four gas giant planets be aligned in a straight line? What if you wanted to put in there with a 500-year orbit and send it in there with a 15,000 year orbit?”
I guess this is the grand tour that the Voyager spacecraft did when they visited all of the giant planets, right? The planets were kind of lined up so that the Voyager spacecraft could go past Jupiter, get a gravitational assist; go past Saturn, get a gravitational assist.
Voyager I went out of the solar system. Voyager II went on to Uranus and then on to Neptune. It was a very rare alignment of all the planets. How often does that kind of thing happen?
Pamela: That simple alignment that Voyager was able to experience that luckily occurs every 175 years. Trying to get those extra worlds out there, I won’t say they’re planets, I won’t say they’re not, those extra icy bodies out there trying to get those aligned I wasn’t actually able to Google those numbers or find a quick journal article on it.
You’re now starting to bring in a 500 and a 1500 year cycle as well and so those are the types of things that at most will happen every 15,000 years and probably not that likely. This is a good homework problem for a celestial mechanic hanging out in our audience.
Fraser: But in many cases, it is the last planet that’s really calling the shots here?
Fraser: How often is that last planet in the planet inside it lining up? Jupiter and Saturn line up fairly regularly. Jupiter, Saturn and Uranus lining up really depends on Uranus’ orbit. The same thing to get all four lined up and so on. It’s really going to be Sedna that needs to be lined up.
Pamela: The convenient thing about Sedna is it is moving so slowly that essentially once you get it where you need it you can wait that 175 years for the inner gas giants because it is just moving slowly. It will be somewhere 15,000 plus or minus that you get this line
Fraser: One hundred and seventy-five years, right so you’re going to get every 15,000 years you’re going to get Sedna and Uranus lined up.
Fraser: Then 50 or 70 years after that you’re going to get Neptune in and then 15 years after that Saturn’s going to come into play so then you’re going to get Jupiter.
Pamela: The problem that you get is wh
Fraser: Still, Voyager was the chance of our lifetime to build and send one spacecraft at all four planets. That’s never going to happen for anyone really who is alive today.
Fraser: Fred asks: “Why can’t human eyes detect all the wavelengths? We see in the visible spectrum in a few hundred nanometer wavelength, why can’t we see infrared and why can’t we see ultraviolet and why can’t I see radio waves?”
Pamela: Well, at a certain level it comes down to one very simple factor and that is chemistry. Our human eyes are able to detect light because the energy from the photon hitting the cells in the back of the retina causes a chemical reaction. It is because of this chemical reaction that we’re able to perceive light, that we’re able to perceive different colors.
The chemical reactions are even sensitive as to what color is hitting them in particular. For instance it is possible that someone could have some weird mutation that makes them a little bit more sensitive in one direction or the other and gives them special sensitivities into the ultraviolet or the infrared just because the chemical reactions are off somehow.
It is still chemistry where to get that sort of change you’d need to have different proteins getting formed, different reactions occurring within the eye. It would have to be one heck of a serious mutation.
That will get you a little ways into the infrared or the ultraviolet but if you wander too far, you start worrying about things like “well, I’m now trying to detect radio waves which are meters to more in length when you start hitting the extremes and at least centimeters in wavelength at the smaller ends.”
With an eyeball that is what a centimeter at most in retina opening or in pupil opening so when you start dealing with a detector that is so much smaller than your wavelength it becomes very hard to make good detections.
You have this combination of chemistry and the size of the detector that makes it not possible because of the chemistry. Even if you did take and change the chemistry you’d start running into difficulties because of the size of the detector.
Fraser: Then to really detect outside of what we do we need electronics. [Laughter]
Pamela: Yes and we have those luckily.
Fraser: This question comes fromfrom Newmarket, Ontario Canada: “On National Geographic they stated that at 5 billion years the universe will basically break up and all the particles will disintegrate. What will happen if the universe will end what would there be? I can’t picture anything; even nothing in my mind would just be black. But if there is absolutely nothing, where does the black come from?”
I think there are a few mistakes in the questions. I’m not sure what National Geographic is telling people but they’re wrong.
Pamela: Yeah I think it is more like 50 trillion years.
Fraser: Fifty trillion years, like one to the power of a hundred when the universe will finally kind of die. We did a two part show on this called “The End of Everything”.
In the first half we covered the end of the solar system and in the second half we talked about the very end of the universe and how things will play out. We’ve got that but I think we can kind of give the quick version.
Pamela: Which are eventually protons themselves will start to fall apart. When the protons themselves fall apart, we’re left with a universe of nothing but very cold and depressing energy.
The universe just basically becomes this fizzled out place of nothing. All the black holes have evaporated. All of the protons have fallen apart and space is so big at that point that the energy can’t condense into anything else.
The energy just sort of spreads itself out. It is sad, it is cold, and it is depressing.
Fraser: The black is just coming from the fact there is no appreciable electromagnetic radiation going past to bump into any detector. The whole universe will be stretched way out and photons will be light years across and there will be no way to actually see anything.
If you were to hop in a time machine and pop into the future with a flashlight and then point it at your face you would be able to see the light, right?
Fraser: The universe would still function and if you could introduce some new matter and energy into it then that would all just work fine. The reality is the black would come from the fact that there is nothing to see.
When you go into a very dark room and you turn off the light there’s nothing to see and so you don’t see anything and that’s the blackness. Your eyes still work but there’s no light.
Pamela: This is where it is just important to remember that black in terms of astronomy is nothing more than the lack of light. That’s all it is – no light.
Fraser: Right or lack of electromagnetic radiation, no radio, no infrared
Pamela: Which is still light.
Fraser: Yeah it’s all just still light, different wavelengths. There’s just no nothing. For the even sadder more depressing version we highly recommend you listen to “The End of Everything” and we cover that.
It is pretty sad though so make sure you’re ready for a very sad [Laughter] and depressing episode.
Fraser: The next one comes fromfrom Bucharest, Rumania: “While listening to the podcast I heard that hot objects give off blue light and cold ones give off red light which contradicts what I knew before. I told my high school teacher and asked is this true? She said it was the other way around. So, how is it actually?
If hot objects give off blue light, why do infrared cameras show us the opposite?” Let’s untangle this. Do cool objects give off red light and hot objects give off blue light?
Fraser: Okay and that matches stars, right? A cool star is red. A medium star is white and a hot star is blue.
Pamela: Right and I think I know where the confusion came in. When we’re little, little kids we are taught somewhere along the lines that cold icy days should be drawn with a blue crayon and really hot fires and stoves should be drawn with a red crayon. This sticks in our brain so that when we’re making color graphs we do where there are a lot of people red; where there are not that many people blue.
When we’re doing pictures we do if we’re mapping temperature to the map we do the hot areas of the map as red and the cold areas of the map as blue if it is artificial color. With infrared cameras what they often do is they fake the color. They make the cheeks the hot parts of your face bright red in some of the color schemes.
Fraser: And cooler is yellow and cooler than that is blue. That’s right, so it is backwards isn’t it?
Pamela: Yeah and so it is a matter of there is this thing calledwhich mathematically describes the color of light that an object gives off most of its energy at or it gives off the most energy at rather as a function of temperature.
As you turn up the temperature that point where there is the most photons in a graph of photons versus or number of photons versus temperature that color that you get that peak at moves bluer and bluer and bluer as you increase the temperature.
We still are trained that with our crayon red is hot and blue is cold. Scientists tend to still think that way when we color our maps. You can even go out and find maps of the cosmic microwave background where they refer to the hot spots as red and the cold spots as blue.
It is deceiving, we’re sorry. We’ll think harder next time.
Fraser: If you’re in theater or if you’re in photography and you’re trying to take pictures you know that you want your light to be redder. People in graphic arts know above the temperature of light. They know that the hotter the light the bluer it is. The cooler the light the redder it’s going to be.
They might say the light is too blue or the light is too red because it is the wrong temperature and it does. It goes from red to white to blue. Blue being hottest and above blue just goes off into ultraviolet.
Pamela: We know it and we just have a tendency to make graphs that confuse people and we apologize for doing that. Or at least I apologize on behalf of everyone.
Fraser: On behalf of all those people. So when you see a picture of an infrared camera that is a completely computer-generated version of light. That’s not really what is being seen. That’s just the camera is for us poor human beings who can’t see in infrared. Otherwise it just wouldn’t even bother, right? It would just keep it in infrared.
Fraser: It is cooler here and hotter over there and we should be able to see it with our snake eyes [Laughter] but we can’t. The computer has to actually translate it. For some reason blue seems to be considered to be cool and red is hot. That’s really cool, it is a great question.
I think we’re done for this week. Thanks a lot Pamela. Thanks to everybody who sent in the questions and we will talk to you on our next show.