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And it is experiencing an active volcano. Lava or magma is flowing from underneath the ground. And once it surfaces, we call it lava. And that lava is actively making the island bigger. So where is that volcanic activity coming from? And then how can we think about that volcanic activity or that kind of heat rising fro... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
And that lava is actively making the island bigger. So where is that volcanic activity coming from? And then how can we think about that volcanic activity or that kind of heat rising from below the surface of the earth to explain some of the geological features we see around Hawaii? So what we think is happening, and o... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
So what we think is happening, and once again, this is all theory right here, is that Hawaii is sitting on top of a hotspot. In particular, the big island of Hawaii is sitting on top of the hotspot right now. And this hotspot, there's different theories on how it might emerge. But we think that at the mantle core bound... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But we think that at the mantle core boundary, and I don't know in this diagram whether they intended this white area to be the core, but let's just say that this is the outer core down here. So let's just say that this is the outer core for the sake of explaining things. It's possible that plumes of very hot material ... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
Let me do this in a darker color. Can rise up from the outer core. They would rise up from the outer core and then create hotspots underneath the moving lithospheric plates. Now, we don't know for sure whether the hotspots are being created by these mantle plumes, this material formed or heated up at the outer core man... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
Now, we don't know for sure whether the hotspots are being created by these mantle plumes, this material formed or heated up at the outer core mantle boundary. But what we do feel pretty confident about is that there is this hotspot here. And it's independent of any of those convection patterns that we saw. I shouldn't... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
I shouldn't say independent. It's obviously all related because we have all this fluidic motion going on in the mantle. But it's separate on some degree from all of those convection patterns that we talked about that would actually cause the plates to move. And to a large degree, or the way we think about it right now,... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
And to a large degree, or the way we think about it right now, this is stationary. This hotspot is stationary relative to the plates. And the reason why we feel pretty good about thinking that it's stationary relative to the plates is we see this notion right here. If you look at the volcanic rock in Kauai, which is on... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
If you look at the volcanic rock in Kauai, which is one of the older inhabited Hawaiian islands, the oldest rock that we've observed there is 5.5 million years old. And it's all volcanic rock. Now, the oldest rock we've observed on the big island is about 700,000 years old. We also know that the Pacific plate, you coul... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
We also know that the Pacific plate, you could look at this diagram right over here, is moving in this general direction. In fact, we know it from GPS measurements. It's moving exactly in the direction that the Hawaiian islands are kind of distributed in. So frankly, the only good explanation for why we see this patter... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
So frankly, the only good explanation for why we see this pattern, why we see newer land here, and then as we go further and further up the Hawaiian island chain, we see older and older land. And actually, if we keep going, we have the Leeward Islands over here. And as we keep measuring the rock on the Leeward Islands,... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
And then if you even look at what's below the ocean, this is the big island of Hawaii. These are the main Hawaiian islands. These are the Leeward Islands. But you see, even beyond that, submerged under the Pacific Ocean, you continue to see a chain of islands. So the explanation for what's happening here is that you ha... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But you see, even beyond that, submerged under the Pacific Ocean, you continue to see a chain of islands. So the explanation for what's happening here is that you have a stationary hotspot that is right now underneath the big island of Hawaii. And I just want to be clear. The big island is called the island of Hawaii. ... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
The big island is called the island of Hawaii. It is one of the islands in the state of Hawaii. So I don't want to cause you confusion. I'll just call it the big island from here on out. So the hotspot is right under the big island. But if you were to rewind 5 million years ago, the entire Pacific plate was probably on... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
I'll just call it the big island from here on out. So the hotspot is right under the big island. But if you were to rewind 5 million years ago, the entire Pacific plate was probably on the order of about 150, 200 miles, however far Kauai is from the big island. It was probably shifted that much to the southeast if you ... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
It was probably shifted that much to the southeast if you go back 5 million years ago. So 5 million years ago, when all of this was shifted down and to the right, then Kauai was on top of the hotspot. And so this is how each of these islands are formed. If you rewind a ton of years, then maybe this area over here on th... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
If you rewind a ton of years, then maybe this area over here on the Pacific plate was over the hotspot. An island formed there. Then the Pacific plate kept moving to the northwest. And new islands, new volcanoes kept forming. Those volcanoes would release lava that would keep piling up, eventually go above the surface ... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
And new islands, new volcanoes kept forming. Those volcanoes would release lava that would keep piling up, eventually go above the surface of the water and form this whole chain of islands. And as the whole Pacific plate kept moving to the northwest, it kept forming new islands. Now the one question you might ask is, w... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
Now the one question you might ask is, well, how come the big island is bigger? Has the plate kind of paused over there? Is it spending more time over the hotspot so that more lava can kind of form there to form this? Essentially, it's an underwater mountain that's now also above the water. And actually, if you go from... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
Essentially, it's an underwater mountain that's now also above the water. And actually, if you go from the base of the Pacific Ocean to the top of the big island of Hawaii, it's actually 50% higher than Mount Everest. So you could really just view it as a big mountain. But the question is, this looks so much bigger tha... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But the question is, this looks so much bigger than Kauai, and they keep getting smaller as you keep going to the northwest. Is somehow the Pacific plate slowing? Is it spending more time here? And the answer is, it's probably not slowing. What's happening is, at one time, Kauai was also probably a relatively large isl... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
And the answer is, it's probably not slowing. What's happening is, at one time, Kauai was also probably a relatively large island. If you rewind maybe 5 million years ago, Kauai also might have been about that big. But over 5 million years, it's just experienced a ton of erosion. Remember, once it moved over the hotspo... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But over 5 million years, it's just experienced a ton of erosion. Remember, once it moved over the hotspot, new land wasn't being created. It's in the middle of the Pacific Ocean. It's experiencing weather. 5 million years is a long period of time. And so it just got eroded over that time. So the older the island is, t... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
It's experiencing weather. 5 million years is a long period of time. And so it just got eroded over that time. So the older the island is, the more eroded it's going to be, and the smaller it's going to be. So if you go to these underwater mountains up here that don't even surface above the ocean, at one time, they mig... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
So the older the island is, the more eroded it's going to be, and the smaller it's going to be. So if you go to these underwater mountains up here that don't even surface above the ocean, at one time, they might have surfaced. But due to the ocean and weather and whatnot, they've just been eroded over time to become sm... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
So anyway, I thought you would find that entertaining of how the Hawaiian Islands actually got formed and how we can actually have these hotspots and this volcanic activity and actually even earthquake activity outside of actually plate boundaries. Actually, while we're looking at this diagram, we talked about the tren... | Hawaiian islands formation Cosmology & Astronomy Khan Academy.mp3 |
But there is no year zero. Right after that you go from December 31, 1 BC to January 1, 1 AD. There's no year zero. And despite the fact that I emphasized that in the last video, I didn't take that into consideration when I calculated how many years there were between Plato's birth and Columbus discovering the New Worl... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
And despite the fact that I emphasized that in the last video, I didn't take that into consideration when I calculated how many years there were between Plato's birth and Columbus discovering the New World. And the reason why I didn't take that into consideration is that the year 1492, whether you want to call it AD 14... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
It is 1491 years since the birth of Jesus. And to think about it this way, let's just assume, I'll keep emphasizing, it's a theoretical date that we're talking about, this theoretical event, this kind of birth of Jesus that our calendars revolve around. If we talk about January 1, let's think about it this way, so Janu... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
It's not one year. You wouldn't just look at this and say it's been one year, because this is theoretically the day that he was born, so this is zero years or almost zero years since that theoretical birth of Jesus. Another way to think about it is, how long after January 1, the year 1 before the Common Era, and I coul... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
The way I calculated it before, I said this is one year after that theoretical birth, that's wrong, this is during that theoretical birth. But the way I did it in the last video, I said that's one year after, one year before, you add them together and you would get 2. But that's wrong, because there is no year zero, so... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
The reason why the math is strange is because there is no year zero. If there was a year zero, then my calculation in the last video was correct. So really, the way that you would calculate the time between Plato's birth at 428 BC and Columbus sailing across the Atlantic in 1492, you would say, okay, this is 428 years ... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
But this isn't 1492 years after that theoretical birth, this is 1492 minus 1. So what you would do is you would add these two numbers, this is 428 before, this is 1492 minus 1 years after, so you would add them and then subtract 1. So the correct answer, this is the correction part, it isn't 1920 years between Plato's ... | Correction calendar notation Cosmology & Astronomy Khan Academy.mp3 |
And when the pressure and the temperature got high enough, and so this is what we saw in the last video, when the pressure and temperature got high enough, we were able to get the hydrogen protons, the hydrogen nucleuses, close enough to each other, or hydrogen nuclei, close enough to each other for the strong force to... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
What I want to do in this video is to take off from that starting point and think about what happens in the star next. So in the main sequence, we have the core of the star. So this is the star's core. And you have hydrogen fusing into helium. And it's releasing just a ton of energy. And that energy is what keeps the c... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And you have hydrogen fusing into helium. And it's releasing just a ton of energy. And that energy is what keeps the core from imploding. It's kind of the outward force to offset the gravitational force that wants to implode everything, that wants to crush everything. And so you have the core of a star, a star like the... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It's kind of the outward force to offset the gravitational force that wants to implode everything, that wants to crush everything. And so you have the core of a star, a star like the sun. And that energy then heats up all of the other gas on the outside of the core to create that really bright object that we see as a s... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now, as the hydrogen is fusing into helium, you can imagine that more and more helium is forming in the core. So I'll do the helium as green. So more and more helium forms in the core. The closer you get to the center, the higher the pressures will be and the faster that this fusion, this ignition, will happen. In fact... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
The closer you get to the center, the higher the pressures will be and the faster that this fusion, this ignition, will happen. In fact, the bigger the mass of the star, the more the pressure, the faster the fusion occurs. And so you have this helium building up inside of the core as this hydrogen in the core gets fuse... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now, what's going to happen there? Helium is a more dense atom. It's packing more mass in a smaller space. So as more and more of this hydrogen here turns into helium, what you're going to have is the core itself is going to shrink. So let me draw a smaller core here. So the core itself is going to shrink. And now it h... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So as more and more of this hydrogen here turns into helium, what you're going to have is the core itself is going to shrink. So let me draw a smaller core here. So the core itself is going to shrink. And now it has a lot more helium in it. And let's just stick it to the extreme point where it's all helium, where it's ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And now it has a lot more helium in it. And let's just stick it to the extreme point where it's all helium, where it's depleted. But it's been shrinking. It's much denser. That same amount of mass that was in this sphere is now in a denser sphere, in a helium sphere. So it's going to have just as much attraction to it,... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It's much denser. That same amount of mass that was in this sphere is now in a denser sphere, in a helium sphere. So it's going to have just as much attraction to it, gravitational attraction. But things can get even closer to it. And we know that the closer you are to a mass, the stronger the pull of gravity. So then ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But things can get even closer to it. And we know that the closer you are to a mass, the stronger the pull of gravity. So then instead of having just the hydrogen fusion occurring at the core, you're now going to have hydrogen fusion in a shell around the core. So now you're going to have hydrogen fusing in a shell aro... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So now you're going to have hydrogen fusing in a shell around the core. Let me just be clear. This isn't just happens all of a sudden. It is a gradual process. As we have more and more helium in the core, the core gets denser and denser and denser. And so the pressures become even larger and larger near the core. Becau... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It is a gradual process. As we have more and more helium in the core, the core gets denser and denser and denser. And so the pressures become even larger and larger near the core. Because you're able to get closer to a more massive core since it is now more dense. And as that pressure near the core increases even more ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Because you're able to get closer to a more massive core since it is now more dense. And as that pressure near the core increases even more and more, the fusion reaction happens faster and faster and faster. Until you get to this point. So here, let me be clear. You have a helium core. All of the hydrogen in the core h... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So here, let me be clear. You have a helium core. All of the hydrogen in the core has been used up. And then you have the hydrogen right outside of the core is now under enormous pressure. It's actually under more pressure than it was when it was just a pure hydrogen core. Because there's so much mass on the outside he... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And then you have the hydrogen right outside of the core is now under enormous pressure. It's actually under more pressure than it was when it was just a pure hydrogen core. Because there's so much mass on the outside here trying to, I guess you could say, exerting downward or gravitational force. Down trying to get to... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Down trying to get to that even denser helium core. Because everything is able to get closer in. And so now you have fusion occurring even faster. And it's occurring over a larger radius. So this faster fusion over a larger radius is then going to expel, the force is now going to expel, the energy that's released from ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And it's occurring over a larger radius. So this faster fusion over a larger radius is then going to expel, the force is now going to expel, the energy that's released from this fusion is now going to expel these outer layers of the star even further. So the whole time, this gradual process, as the hydrogen turns into ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It starts to, or I shouldn't say burn, it starts to fuse faster and faster. And over a larger and larger radius. So the unintuitive thing is the fusion is happening faster over a larger radius. And the reason that is is because you have even a denser core that is causing even more gravitational pressure. And as that's ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And the reason that is is because you have even a denser core that is causing even more gravitational pressure. And as that's happening, the star is getting brighter. And it's also the fusion reactions, since they're happening in a more intense way and over a larger radius, are able to expel the material of the star ev... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So the radius of the star itself is getting bigger and bigger and bigger. So if this star would look like this, if this star, maybe let me draw it in white, this star looked like this. That's not white. This star looked like, what's happening to my color changer? There you go. OK, this star looked like this right over ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
This star looked like, what's happening to my color changer? There you go. OK, this star looked like this right over here. Now this star over here, since a faster fusion reaction is happening over a larger radius, is going to be far larger, and I'm not even drawing it to scale. In the case of our sun, when it gets to t... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now this star over here, since a faster fusion reaction is happening over a larger radius, is going to be far larger, and I'm not even drawing it to scale. In the case of our sun, when it gets to this point, it's going to be 100 times the diameter. And at this point, it is a red giant. And the reason why it's redder th... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And the reason why it's redder than this one over here is that even though the fusion is happening more furiously, that energy is being dissipated over a larger surface area. So the actual surface temperature of the red giant at this point is actually going to be cooler. So it's going to emit a light at a larger wavele... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
This thing, the core, was not burning as furiously as this thing over here, but that energy was being dissipated over a smaller volume. So this had a higher surface temperature. This over here, the core is no longer burning. The core is now helium that's not burning. It's getting denser and denser as the helium packs i... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
The core is now helium that's not burning. It's getting denser and denser as the helium packs in on it itself, but the hydrogen fusion over here is occurring more intensely. It's occurring in a hotter way, but the surface here is less hot because it's just a larger surface area. So the increased heat is more than mitig... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So the increased heat is more than mitigated by how large the star has become. Now this is going to keep happening, keep happening, and the pressures keep intensifying because more and more helium is getting produced. And this core keeps collapsing, and the temperature here keeps going up. So we said that the first ign... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So we said that the first ignition, the first fusion occurs at around 10 million Kelvin. This thing will keep heating up until it gets to 100 million Kelvin. And now I'm talking about a star that's about as massive as the sun. Some stars will never even be massive enough to condense the core so that its temperature rea... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Some stars will never even be massive enough to condense the core so that its temperature reaches 100 million. But let's just talk about the case in which it does. So eventually you'll get to a point, so we're still sitting in the red giant phase. So we're this huge star over here. We have this helium core, and that he... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So we're this huge star over here. We have this helium core, and that helium core keeps getting condensed and condensed and condensed. And then we have a shell of hydrogen that keeps fusing into helium around it. So this is our hydrogen shell. Hydrogen fusion is occurring in this yellow shell over here that's causing t... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So this is our hydrogen shell. Hydrogen fusion is occurring in this yellow shell over here that's causing the radius of the star to get bigger and bigger to expand. But when the temperature gets sufficiently hot, and now I think you're going to get a sense of how heavier and heavier elements form in the universe. And a... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And all of the heavy elements that you see around us, including the ones that are in you, were formed this way from initially hydrogen. When it gets hot enough at 100 million Kelvin in this core, because of such enormous pressures, then the helium itself will start to fuse. So then we're going to have a core in here wh... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And now we're talking about a situation, you have helium and you had hydrogen, and all sorts of combinations will form, but in general, the helium is mainly going to fuse into carbon and oxygen. And it will form into other things, and it becomes much more complicated, but I don't want to go into all of the details. But... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
I didn't have this in the last one. I somehow lost it. But we see hydrogen here has one proton. It actually has no neutrons. It was getting fused in the main sequence into helium. Two protons, two neutrons. We would need four of these to get one of those, because this actually has an atomic mass of 4, if we're talking ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It actually has no neutrons. It was getting fused in the main sequence into helium. Two protons, two neutrons. We would need four of these to get one of those, because this actually has an atomic mass of 4, if we're talking about helium-4. And then the helium, once we get to 100 million Kelvin, can start being fused. I... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
We would need four of these to get one of those, because this actually has an atomic mass of 4, if we're talking about helium-4. And then the helium, once we get to 100 million Kelvin, can start being fused. If you get roughly three of them, and there's all these other things that are coming and leaving the reactions, ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
You get four of them, at least as the starting raw material, you get to an oxygen. So we're starting to fuse heavier and heavier elements. So what happens here is this helium is fusing into carbon and oxygen, so you start building a carbon and oxygen core. So I'm going to leave you there. I realize I'm already past my ... | Becoming a red giant Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
In the last video, we learned that 380,000 years after the Big Bang, which is still roughly 13.7 billion years ago, every point, I shouldn't say every point, every atom in space that was kind of at this roughly 3,000 Kelvin temperature was emitting this electromagnetic radiation. Since every point in space was, there w... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So when we look at radiation that's been traveling for that long, we can look in any direction and we'll see this uniform radiation. And that radiation has been redshifted into the microwave range from the higher frequencies that it was actually emitted at. Now, a question that might pop in your brain is, well, what ha... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Because if we wait a billion years, if we have a billion 380,000 years after the beginning of the universe, this stuff won't just be atoms anymore. It will have started to condense into actual stars. We would not, the universe at every point in space will no longer be this uniform. We'll actually start having condensat... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We'll actually start having condensation into stars. So if we go, the universe, if we move forward a little bit, the universe will expand. Maybe I'll just draw half of it since it's expanded. It's obviously expanded much more. But now all of a sudden, we actually have stars. These are no longer just uniform atoms sprea... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
It's obviously expanded much more. But now all of a sudden, we actually have stars. These are no longer just uniform atoms spread through the universe. We actually have condensation into stars. And so if you look at what is being emitted from the points in space from which we're only now getting this cosmic background ... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We actually have condensation into stars. And so if you look at what is being emitted from the points in space from which we're only now getting this cosmic background radiation, if we wait a billion years, the light that we see from those points in space will not look like this uniform radiation. It'll start to look a... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
It'll start to, we'll essentially be looking at the universe a billion years after the Big Bang when stars have formed, other structures have formed. So the question is, in a billion years, will this cosmic microwave background radiation disappear? And I'm using the billion just because that's just to arbitrarily use a... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
But will it eventually disappear? And there's kind of, the answer to that is yes and no. So to think about it, it is true that this point in space will mature. It will mature in a billion years. It will no longer be this uniform haze of hot hydrogen atoms. But what you have to think about is, there were further points ... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
It will mature in a billion years. It will no longer be this uniform haze of hot hydrogen atoms. But what you have to think about is, there were further points in the universe. There were further points in the universe. At that same time, there were further points that were also emitting this radiation. And the origina... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
There were further points in the universe. At that same time, there were further points that were also emitting this radiation. And the original photons from those original points still haven't gotten to us. So from those further out points, right now the observable universe is, we can only see electromagnetic radiatio... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So from those further out points, right now the observable universe is, we can only see electromagnetic radiation that's been traveling for 13.7 billion years. In another billion years, the universe will be a billion years older. And then there will be radiation that has been traveling for 14.7 billion years. And so we... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
And so we will start to observe that. And we'll start to observe that radiation from the same time period in the universe. It will just be from further out. Now, what I want to make clear is that since those points were even further out, where that radiation was emitted, the stuff that we'll see in a billion years, it ... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Now, what I want to make clear is that since those points were even further out, where that radiation was emitted, the stuff that we'll see in a billion years, it will be even more redshifted. So at that point, the cosmic background radiation we see will have longer wavelengths than the radio spectrum. It will be redde... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
And I should say redder, because we're already more. Would redder have two D's? I've never written redder. Well, it would be more red than the microwave radiation. And of course, that's a funny thing, because microwave radiation is already more red than actual visible red light. It has a longer wavelength. Now, this wi... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Well, it would be more red than the microwave radiation. And of course, that's a funny thing, because microwave radiation is already more red than actual visible red light. It has a longer wavelength. Now, this will keep happening. And I don't know what, you know, it'll keep happening. We'll keep getting radiation as w... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Now, this will keep happening. And I don't know what, you know, it'll keep happening. We'll keep getting radiation as we go further and further into the future. We'll keep getting radiation from further out points in space. And it'll get more and more redshifted. The actual wavelengths of that electromagnetic light wil... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We'll keep getting radiation from further out points in space. And it'll get more and more redshifted. The actual wavelengths of that electromagnetic light will be bigger and bigger and bigger, until we really aren't able to even see it as electromagnetic light, because it'll be redshifted to infinity. It'll have an in... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
It'll have an infinite wavelength. And to make that point clear, I want to show you that there'll even be points, at some point, there'll be kind of a threshold where we can't even get radiation from further out. And let me show you. Let me draw a diagram of that. So let's say that this is the universe 13.7 billion yea... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Let me draw a diagram of that. So let's say that this is the universe 13.7 billion years ago, right when that radiation, what we now see as cosmic microwave background radiation, right when it started to be emitted. And let's say that this is the point in the universe where we are now. So this is us. Let's say that thi... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So this is us. Let's say that this is the point in the universe that where we now observe the background radiation. Or this is one of the points. We obviously could form a circle around us. It could be any of these points over here. We're only where the photons, the electromagnetic radiation that were emitted from this... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We obviously could form a circle around us. It could be any of these points over here. We're only where the photons, the electromagnetic radiation that were emitted from this point 380,000 years after the beginning of the universe, is only just now reaching us. So this is the point in the universe from which we are obs... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So this is the point in the universe from which we are observing the cosmic background radiation. And let me be very clear. That point in the universe has now matured into things that look into stars and galaxies and planets. And if they were to look at our point in space, they are also going to see cosmic background r... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
And if they were to look at our point in space, they are also going to see cosmic background radiation from us. It's not like this is some type of permanently old place. It's just the light we're getting from them right now is old light, light that that point in space emitted way before it was able to mature into actua... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So this is the point in space from which we are receiving cosmic background radiation right now. I don't want to write all that. It'll take me forever. Now, let's take another point in space that's whatever this distance is. Well, it's actually estimated to be about now. It's estimated to be about 46 billion light year... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Now, let's take another point in space that's whatever this distance is. Well, it's actually estimated to be about now. It's estimated to be about 46 billion light years. At that time, when things were just beginning to be emitted, this was only about 36 million light years. And this is a very rough estimate. I shouldn... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
At that time, when things were just beginning to be emitted, this was only about 36 million light years. And this is a very rough estimate. I shouldn't even write it down, because that's really based on how fast we assume the universe is expanding and all of that type of thing. But it was just a lot smaller than 46 bil... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
But it was just a lot smaller than 46 billion light years. Now, let's go that same distance again from this point in space. So let me make it clear. This is 380,000 years ago. Now, let's fast forward. Let's fast forward. Sorry, not 380,000 years ago. | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
This is 380,000 years ago. Now, let's fast forward. Let's fast forward. Sorry, not 380,000 years ago. 380,000 years after the Big Bang, which is approximately, it's still 13.7 billion years ago. So that's then. Now, let's look at now. | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Sorry, not 380,000 years ago. 380,000 years after the Big Bang, which is approximately, it's still 13.7 billion years ago. So that's then. Now, let's look at now. Now, I'll just draw it a little bit bigger. It's actually going to be much, much bigger now. Now, if we do it a little bit bigger, so when I draw it like thi... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Now, let's look at now. Now, I'll just draw it a little bit bigger. It's actually going to be much, much bigger now. Now, if we do it a little bit bigger, so when I draw it like this, this is where we are now. This point in space is this point in space from which we are only now receiving that cosmic background radiati... | Cosmic background radiation 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
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