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That's a huge amount of time. So hopefully that put things in perspective a little bit. What I want to do in this video is kind of do the same thing, but relate the 13.7 billion years, if that were a distance or the length of a timeline, how big each of these periods would be. So just to start off, the timeline, I'm re... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So just to start off, the timeline, I'm recording this in high definition right now. There should be 1,280 pixels wide, depending on where you're watching it. So maybe you're watching it on a high def TV. If the timeline was the width of my screen right over here, so if that was 13.7 billion years from there, let's say... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
If the timeline was the width of my screen right over here, so if that was 13.7 billion years from there, let's say this is the beginning of the universe and this is our present time. If that was 13.7 billion years, the amount of time that humans have been on this planet, modern humans, the people who look and think li... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
The amount of time we've been here would not even be a pixel. In fact, a pixel, and that dot I drew here is about 4 pixels, but a pixel, just one little pixel on my screen, would represent 11 million years. 11, let me scroll over, it would represent 11 million years. So if this was the timeline, the dinosaurs would hav... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So if this was the timeline, the dinosaurs would have been extinct about 6 pixels from the end. When the dinosaurs would have gotten extinct, and the amount of time that modern humans are on the planet wouldn't even register here. It would be 1 20th of that pixel over there. In fact, if we just expanded that very last ... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
In fact, if we just expanded that very last pixel, I'll do it in yellow, that very last tiny pixel that you can't see, if we were to expand that to the entire length of this screen again, so if we were to just expand just that very last pixel, so I'm saying everything on this yellow line could be contained in that very... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Not even that. So 25 pixels on this screen, at least at my resolution, is about that distance. So this is the fraction of just that pixel. That is the amount of time humans have been on the planet. If you want the time since Jesus, it would be 1 4th of a pixel on this yellow scale. On this yellow scale, it would be 1 4... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
That is the amount of time humans have been on the planet. If you want the time since Jesus, it would be 1 4th of a pixel on this yellow scale. On this yellow scale, it would be 1 4th of a pixel. And the amount of time since the Declaration of Independence would be even a more minuscule amount of time. So that's one wa... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
And the amount of time since the Declaration of Independence would be even a more minuscule amount of time. So that's one way to think about it. But these timelines, to some degree, also don't give justice. So another way to think about it, what if we had a timeline that stretched from here, where I am, in the San Fran... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So another way to think about it, what if we had a timeline that stretched from here, where I am, in the San Francisco Bay Area, if it stretched 1,300 kilometers to Seattle. So if this thing stretched 1,300 kilometers all the way to Seattle, then how? So this thing, the Big Bang, would be sitting in Seattle. Well, the ... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
Well, the formation of the Earth and the solar system, this would be about 200 kilometers away, a little over 200 kilometers. And in the direction of Seattle, I don't know, that would get us in probably some part of northern California with redwoods and whatnot. But just to give an idea of 200 kilometers, that would ge... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So still a pretty good distance relative to the entire timeline. The last land dinosaurs, when the Earth got hit by an asteroid, this, so remember, our whole timeline now stretches all the way to Seattle. This event now would have only occurred about 3,000 meters away, or maybe I should just say 3 kilometers away, or r... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So that still seems like a pretty good distance. But remember, our timeline stretches all the way to Seattle from the San Francisco area. So it's a pretty big timeline. So this is already a pretty small distance. But it gets even smaller. Australopithecus, this right over here, when they were roaming the Earth 3 millio... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
So this is already a pretty small distance. But it gets even smaller. Australopithecus, this right over here, when they were roaming the Earth 3 million years ago, this gets reduced to a little bit more than a football field. About 150 meters, not kilometers. Let me write that in a color where there's some contrast. 15... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
About 150 meters, not kilometers. Let me write that in a color where there's some contrast. 150 meters is where, so 150 meters in the direction of Seattle, if that's the timeline that we're talking about. And then the first humans, even shorter. It's only going to be 10 meters of this timeline that stretches all the wa... | Cosmological time scale 2 Scale of the universe Cosmology & Astronomy Khan Academy.mp3 |
We've already talked a lot about plate boundaries, where essentially new crust material is being created, and the plates are actually moving apart. We call these divergent boundaries. And the example we showed of this was the Mid-Atlantic Ridge, where essentially new crustal material is being created. Now on the other ... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
Now on the other side of the equation, you have areas where plates are ramming into each other. We see that over here, where the Nazca plate is running into the South American plate. We see it over here, where the Pacific plate is running into the Filipino plate. They're running into each other. So what happens over th... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
They're running into each other. So what happens over there? So what we're going to do is just go through the different scenarios. The general idea is that one plate is going to get subducted under another. They're ramming into each other. One is going to get essentially pushed under the other one. This diagram shows s... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
The general idea is that one plate is going to get subducted under another. They're ramming into each other. One is going to get essentially pushed under the other one. This diagram shows some subduction over here. This is essentially an oceanic plate being subducted under another oceanic plate. So not too different th... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
This diagram shows some subduction over here. This is essentially an oceanic plate being subducted under another oceanic plate. So not too different than what might happen where the Pacific plate runs into the Filipino plate right over here. And then on this side of the diagram, we see an oceanic plate and the oceanic ... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And then on this side of the diagram, we see an oceanic plate and the oceanic crust getting subducted under a continental plate right over here. And this is what's happening when the Nazca plate is getting subducted under the South American plate. And when that happens, a couple of things. So you have the oceanic plate... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
So you have the oceanic plate being pushed under. And what happens at the same time, the continental plate gets pushed upwards, causing mountain ranges like the Andes, and that's exactly what has created the Andes. It's that upward force from the Nazca plate being pushed under the South American plate at that coastline... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And what you're also going to see is, and you can imagine, you have these huge plates grinding past each other. And it's not a very smooth process. Every now and then, you kind of reach a breaking point and huge amounts of energy get released. So you're also going to see a lot of earthquakes in those areas. And we know... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
So you're also going to see a lot of earthquakes in those areas. And we know that Chile has a lot of earthquakes. And then on top of that, this is going to result in a lot of heat and a lot of the friction of the plates grinding past each other, essentially allowing magma to form at that part of the rock. Because it's ... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
Because it's getting so heated, and so you'll also have volcanoes in these areas, where essentially something is being subducted underneath a continental plate. Now, we also talked about what's happening in the Pacific, where we have the Pacific plate being subducted under the Filipino plate. That's what we kept referr... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And that's doing a couple of interesting things. Whenever you have subduction, you have trenches. But it's most interesting, or at least in my mind, the deepest trenches have been created where you have an oceanic plate being subducted under another oceanic plate. So a couple of things are going to happen. You're going... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
So a couple of things are going to happen. You're going to have a very deep, you're going to have trenches form. Over here, we see in this diagram, we also have a trench in the first example. But you have trenches form where one oceanic plate is being subducted under another. And then you have that same type of frictio... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
But you have trenches form where one oceanic plate is being subducted under another. And then you have that same type of friction that you saw over here create volcanoes. And those volcanoes will initially be underwater volcanoes, since these are both oceanic plates. Or we're dealing with oceanic crust at that point of... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
Or we're dealing with oceanic crust at that point of the plate. It doesn't have to be entirely an oceanic plate. And they'll first be underwater volcanoes. But as the lava piles up and hardens, it'll eventually turn into a group of islands. And we have that happening where the Pacific plate runs into the Filipino plate... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
But as the lava piles up and hardens, it'll eventually turn into a group of islands. And we have that happening where the Pacific plate runs into the Filipino plate. And first, we have the trench. So let me just draw everything right here. So this is the boundary, roughly speaking, between the two plates. This is the P... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
So let me just draw everything right here. So this is the boundary, roughly speaking, between the two plates. This is the Pacific plate. And this is the Filipino plate, right over here. And so where it's being subducted, you have the Mariana Trench, which is the deepest trench in the world. It goes down 11 kilometers, ... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And this is the Filipino plate, right over here. And so where it's being subducted, you have the Mariana Trench, which is the deepest trench in the world. It goes down 11 kilometers, 11,000 meters. That's deeper than Mount Everest is high. Mount Everest is about 9,000 meters high. And we'll see that's also due to anoth... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
That's deeper than Mount Everest is high. Mount Everest is about 9,000 meters high. And we'll see that's also due to another convergent plate boundary, another place where plates are running into each other. So not only do you see the Mariana Trench here, because one plate is being subducted under the other, you see th... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
So not only do you see the Mariana Trench here, because one plate is being subducted under the other, you see the formation of the Mariana Islands, which are essentially created from underwater volcanoes because of all of the energy being released. And this is actually a depiction of what's the subduction that's happen... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And as lava just goes and starts building these islands. Now the last type of convergent boundary is when you have two parts of continental crust running into each other. So that's the situation that we have where the Indian plate is running into the Eurasian plate. And I think you might already guess what's going to h... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And I think you might already guess what's going to happen there. When you have two pieces of continental crust running into each other, one isn't more or less dense than the other. And so at least the crustal portions of them are just going to keep jamming into each other. And so they're just going to push things upwa... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
And so they're just going to push things upward. This is a depiction right here that I got from the USGS. And what's kind of depicting is this is the Indian plate, this is the Eurasian plate. This is if you rewind a good bit before they've really had a chance to jam into each other. But as they're jamming into each oth... | Plate Tectonics-- Geological features of Convergent Plate Boundaries.mp3 |
A star that started forming a core of iron. It has enormous pressure, enormous inward pressure on this core. Because as we form heavier and heavier elements in the core, the core gets denser and denser and denser. And so we keep fusing more and more elements into iron. This iron core becomes more and more massive, more... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And so we keep fusing more and more elements into iron. This iron core becomes more and more massive, more and more dense. It's squeezing in on itself. And it's not fusing. That is not exothermic anymore. If iron were to fuse, it would not even be an exothermic process. It would require energy. | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And it's not fusing. That is not exothermic anymore. If iron were to fuse, it would not even be an exothermic process. It would require energy. So it wouldn't be even something that could be helped to fend off this squeezing, to fend off this increasing density of the core. So we have this iron here, and it just gets m... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
It would require energy. So it wouldn't be even something that could be helped to fend off this squeezing, to fend off this increasing density of the core. So we have this iron here, and it just gets more and more massive, more and more dense. And so at some mass, already a reasonably high mass, the only thing that's k... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And so at some mass, already a reasonably high mass, the only thing that's keeping this from just completely collapsing is what we could call electron degeneracy pressure. So let me write this here. Electron degeneracy pressure. And all this means is we have all of these iron atoms. We have all of these iron atoms gett... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And all this means is we have all of these iron atoms. We have all of these iron atoms getting really, really, really close to each other. The only thing that keeps it from collapsing at this earlier stage, the only thing that keeps it from collapsing altogether is that they have these electrons. You have these electro... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
You have these electrons, and these are being squeezed together now. We're talking about unbelievably dense states of matter. And electron degeneracy pressure is essentially what it's saying. These electrons don't want to be in the same place at the same time. I won't go into the quantum mechanics of it, but they canno... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
These electrons don't want to be in the same place at the same time. I won't go into the quantum mechanics of it, but they cannot be squeezed into each other anymore. So that, at least temporarily, holds this thing from collapsing even further. And in the case of a less massive star, in the case of a white dwarf, that'... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And in the case of a less massive star, in the case of a white dwarf, that's how a white dwarf actually maintains its shape, because of the electron degeneracy pressure. But as this iron core gets even more massive, more dense, and we get more and more gravitational pressure, so this is our core now, even more gravitat... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Which is essentially the electrons get captured by protons in the nucleus. They start collapsing into the nucleus. It's kind of the opposite of beta negative decay, where you have the electrons get captured, protons get turned into neutrons, you have neutrinos being released, but you can imagine, an enormous amount of ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So this is kind of a temporary, and then all of a sudden this collapses. This collapses even more, until all you have, and all the protons are turning into neutrons, because they're capturing electrons. So then what you eventually have is this entire core is collapsing into a dense ball of neutrons. So dense neutrons. ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So dense neutrons. You can kind of view them as just one really, really, really, really, really massive atom, because it's just a dense ball of neutrons. At the same time, when this collapse happens, you have an enormous amount of energy being released in the form of neutrinos. Did I say that neutrons are being release... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Did I say that neutrons are being released? No, no, no. The electrons are being captured by the protons, protons turning into neutrons, this dense ball of neutrons right here, and in the process neutrinos get released, these fundamental particles. We won't go into the details here. But it's an enormous amount of energy... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
We won't go into the details here. But it's an enormous amount of energy. And this actually is not really, really well understood of all of the dynamics here, because at the same time, that this iron core is undergoing through this, it first kind of pauses due to the electron degeneracy pressure, and then it finally gi... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But when it does it, all of this energy is released. It's not clear how, because it has to be a lot of energy, because remember, this is a massive star, so you have a lot of mass in this area over here. But it's so much energy that it causes the rest of the star to explode outward in an unbelievable, I guess, unbelieva... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And the reason why it's called nova, it comes from, I believe, I'm not an expert here, Latin for new. And the first time people observed a nova, they thought it was a new star, because all of a sudden, something they didn't see before, all of a sudden, it looks like a star appeared, because maybe it wasn't bright enoug... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So just to kind of fathom the amount of energy that's being released in a supernova, it can temporarily outshine an entire galaxy, and in a galaxy, we're talking about hundreds of billions of stars. Or another way to think about it, in that very short period of time, it can release as much energy as the sun will in its... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And so you actually have the material that's not in the core being shot out of the star at appreciable percentages of the actual speed of light. So we're talking about things being shot out at up to 10%, 10% the speed of light. That's 30,000 kilometers per second. That's almost circumnavigating the Earth every second. ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
That's almost circumnavigating the Earth every second. So this is unbelievably energetic events that we're talking about here. And so if the star, if the original star was, and these are rough estimates, people don't have kind of a hard limit here. If the original star is 9 to 20, I'll say approximately 9 to 20 times t... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
If the original star is 9 to 20, I'll say approximately 9 to 20 times the mass of the sun, then it will supernova, and the core will turn into what's called a neutron star. This is a neutron star. Which you can imagine is just this dense ball, it's this dense ball of neutrons. And just to give you a sense of it, it'll ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And just to give you a sense of it, it'll be something about maybe 2 times the mass of the sun, give or take, 1.5 to 3 times the mass of the sun. So this is 1.5 to 3 times the mass of the sun in a volume that has a diameter of about, on the order of tens of kilometers. So roughly the size of a city, in a diameter of a ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So this is unbelievably dense, diameter of a city. I mean, we know how much larger the sun is relative to the earth, and we know how much larger the earth is relative to a city, but this is something more mass than the sun being squeezed into the density or into the size of the city. So unbelievably dense. Now, if the ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now, if the original star is even more massive, if it's more than 20 times the sun, so let me write it over here, let me scroll up. If it's greater than 20 times the sun, then even the neutron degeneracy pressure, even the pressure, even the neutrons' inability to squeeze further will give up and it'll turn into a blac... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
But then you turn into a black hole where essentially all of the mass gets condensed into an infinitely small and dense point, so something unbelievably hard to imagine. And just to give you a sense of it, this will be more mass than even 3 times the mass of the sun, so we're talking about an incredibly high amount of ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
This is the Crab Nebula. This right here is the Crab Nebula. And it's about 6,500 light years away. So it's still, you know, from galactic scale, if you think of our galaxy as being 100,000 light years in diameter, it's still not too far from us on those scales, but it's an enormous distance. The closest star to us is ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So it's still, you know, from galactic scale, if you think of our galaxy as being 100,000 light years in diameter, it's still not too far from us on those scales, but it's an enormous distance. The closest star to us is 4 light years away, and it would take Voyager traveling at 60,000 kilometers an hour 80,000 years to... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
That is 6,500 light years. So this supernova, it's believed happened 1,000 years ago, right at the center. And so at the center here, we should have a neutron star. And this cloud, the shock wave that you see here, this is still the material traveling outward from that supernova over 1,000 years. This shock wave, or th... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And this cloud, the shock wave that you see here, this is still the material traveling outward from that supernova over 1,000 years. This shock wave, or the diameter of the sphere of material, is 6 light years. So we could say this distance right here is 6 light years. So this is an enormously big shock wave cloud. And... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So this is an enormously big shock wave cloud. And actually, we believe that our solar system started to form, it started to condense because of a shock wave created by a supernova relatively near to us. And just to answer another question that was kind of jumping up probably in the last video, and this is still not re... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So you can imagine when the star explodes, a lot of that material is released into the universe. And so that's why we have a lot of these materials in our own bodies. In fact, we could not exist if these heavier elements were not formed inside of the cores of primitive stars, stars that have supernovaed a long time ago... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
Now, the question is, how do these heavier elements form? How do we get all of this other stuff on the periodic table? How do we get all these other heavier elements? And they're formed during the supernova itself. It's so energetic. You have all sorts of particles streaming out and streaming in, streaming out because ... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
And they're formed during the supernova itself. It's so energetic. You have all sorts of particles streaming out and streaming in, streaming out because of the force of the shock wave, streaming in because of the gravity. You have all sorts of kind of a mishmash of elements forming, and that's actually where you have y... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
You have all sorts of kind of a mishmash of elements forming, and that's actually where you have your heavier elements forming. And because, and I'll talk more about this in future videos, most of the uranium, or actually all of the uranium on Earth right now must have been formed in some type of a supernova explosion,... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
So given that it looks to be about 4.6 billion years old, based on how fast it's decayed, and I'll do a whole video on that, that's why we think that Earth was probably, that our solar system was first formed from some type of supernova explosion because that uranium would have been formed right at about the birth of o... | Supernova (supernovae) Stars, black holes and galaxies Cosmology & Astronomy Khan Academy.mp3 |
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