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So this still stays at 14. And now since it now only has 6 protons, this is no longer nitrogen by definition. This is now carbon. And that proton that was bumped off just kind of gets emitted. So then let me just do that in another color. And a proton that's just flying around, you could call that hydrogen-1. And it ca... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And that proton that was bumped off just kind of gets emitted. So then let me just do that in another color. And a proton that's just flying around, you could call that hydrogen-1. And it can gain an electron some ways. If it doesn't gain an electron, it's just a hydrogen ion, a positive ion. Either way, or a hydrogen ... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And it can gain an electron some ways. If it doesn't gain an electron, it's just a hydrogen ion, a positive ion. Either way, or a hydrogen nucleus. But this process, and once again, it's not a typical process. But it happens every now and then. This is how carbon-14 forms. So this right here is carbon-14. | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
But this process, and once again, it's not a typical process. But it happens every now and then. This is how carbon-14 forms. So this right here is carbon-14. You can essentially view it as a nitrogen-14, and one of the protons is replaced with a neutron. And what's interesting about this is this is constantly being fo... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So this right here is carbon-14. You can essentially view it as a nitrogen-14, and one of the protons is replaced with a neutron. And what's interesting about this is this is constantly being formed in our atmosphere. Not in huge quantities, but in reasonable quantities. So let me write this down. Constantly being form... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Not in huge quantities, but in reasonable quantities. So let me write this down. Constantly being formed. Constant formation. And what happens is, and let me be very clear. Let's look at the periodic table over here. Typical carbon. | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Constant formation. And what happens is, and let me be very clear. Let's look at the periodic table over here. Typical carbon. So carbon by definition, if you have 6 protons, carbon by definition has 6 protons. But the typical isotope, the most common isotope of carbon, is carbon-12. So carbon-12 is the most common. | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Typical carbon. So carbon by definition, if you have 6 protons, carbon by definition has 6 protons. But the typical isotope, the most common isotope of carbon, is carbon-12. So carbon-12 is the most common. So most of the carbon in your body is carbon-12. But what's interesting is that a small fraction of carbon-14 for... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So carbon-12 is the most common. So most of the carbon in your body is carbon-12. But what's interesting is that a small fraction of carbon-14 forms, and then this carbon-14 can then also combine with oxygen to form carbon dioxide. And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oce... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And then that carbon dioxide gets absorbed into the rest of the atmosphere, into our oceans. It can be fixed by plants. When people talk about carbon fixation, they're really talking about using mainly light energy from the sun to take gaseous carbon and turn it into actual kind of organic tissue. And so this carbon-14... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And so this carbon-14 makes its way, it's constantly being formed, it makes its way into oceans. It's already in the air, but it completely mixes through the whole atmosphere. Oceans and the air. And then it makes its way into plants. And then it makes its way, and plants are really just made out of that fixed carbon, ... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And then it makes its way into plants. And then it makes its way, and plants are really just made out of that fixed carbon, that carbon that was taken in gaseous form and put into, I guess you could say, into kind of solid form, put into living form. That's what wood pretty much is. It gets put into plants, and then it... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
It gets put into plants, and then it gets put into the things that eat the plants. So that could be us. Now why is this even interesting? I've just explained a mechanism where some of our body, even though carbon-12 is the most common isotope, some of our body, while we're living, gets made up of this carbon-14 thing. ... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
I've just explained a mechanism where some of our body, even though carbon-12 is the most common isotope, some of our body, while we're living, gets made up of this carbon-14 thing. Well, the interesting thing is the only time you can take in this carbon-14 is while you're alive, while you're eating new things. Because... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And what's interesting here is once you die, you're not going to get any new carbon-14, and that carbon-14 that you did have at your death is going to decay via beta decay, and we learned about this, back into nitrogen-14. So this process reverses. So it'll decay back into nitrogen-14, and beta decay, you emit an elect... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
I won't go into the details of that. But essentially what you have happening here is you have one of the neutrons is turning into a proton and emitting this stuff in the process. Now why is this interesting? So I just said while you're living, you have kind of straight-up carbon-14, and carbon-14 is constantly doing th... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So I just said while you're living, you have kind of straight-up carbon-14, and carbon-14 is constantly doing this decay thing. But what's interesting is as soon as you die and you're not ingesting any more plants or breathing from the atmosphere, if you are a plant, or fixing from the atmosphere, and this even applies... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And then you can use that rate to actually determine how long ago that thing must have died. So the rate at which this happens, so the rate of carbon-14 decay is essentially half disappears, half gone in roughly 5,730 years. And this is actually called a half-life. And we talk about it in other videos. This is called a... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And we talk about it in other videos. This is called a half-life. And I want to be clear here. You don't know which half of it's gone. It's a probabilistic thing. You can't just say, oh, all of the carbon-14s on the left are going to decay and all the carbon-14s on the right aren't going to decay in that 5,730 years. W... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
You don't know which half of it's gone. It's a probabilistic thing. You can't just say, oh, all of the carbon-14s on the left are going to decay and all the carbon-14s on the right aren't going to decay in that 5,730 years. What it's essentially saying is any given carbon-14 atom has a 50% chance of decaying into nitro... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
What it's essentially saying is any given carbon-14 atom has a 50% chance of decaying into nitrogen-14 in 5,730 years. So over the course of 5,730 years, roughly half of them will have decayed. Now why is that interesting? Well, if you know that all living things have a certain proportion of carbon-14 in their tissue a... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
Well, if you know that all living things have a certain proportion of carbon-14 in their tissue as kind of part of what makes them up, and then if you were to find some bone, let's just say find some bone right here. You dig it up on some type of archaeology dig. And you say, hey, that bone has one half the carbon-14 o... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
So it would be a pretty reasonable estimate to say, well, that thing must be 5,730 years old. Even better, maybe you dig a little deeper and you find another bone. Maybe you find another bone, maybe a couple of feet even deeper. And you say, wow, this thing right over here has 1 4th the carbon-14. This has 1 4th the ca... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
And you say, wow, this thing right over here has 1 4th the carbon-14. This has 1 4th the carbon-14 that I would expect to find in something living. So how old is this? Well, if it only has 1 4th the carbon-14, it must have gone through two half-lives. After one half-life, it would have one half the carbon. And then aft... | Carbon 14 dating 1 Life on earth and in the universe Cosmology & Astronomy Khan Academy.mp3 |
In the video on black holes, several people asked what is actually a pretty good question, which is if the mass of, say, a black hole is only two or three solar masses, why is the gravity so strong? Obviously, the sun's gravity isn't so strong that it keeps light from escaping. So why would something, or even a star th... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Why would a black hole that has the same mass, why would that keep light from escaping? And to understand that, let's just think a little bit about, and I'll just do Newtonian classical physics right here. I won't get into the whole general relativity of things. And this really will just give us the intuition of why a ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
And this really will just give us the intuition of why a smaller, denser thing of the same mass can exert a stronger gravitational pull. So let's imagine, so let's take two examples. Let's say I have some star here. Let's just call that mass m1. And let's say that its radius, let's just call this r. And let's say that ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Let's just call that mass m1. And let's say that its radius, let's just call this r. And let's say that I have some other mass right at the surface of this star. It's somehow able to survive those surface temperatures. And this mass over here has a mass of m1. This mass over here has a mass of m2. The universal law of ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
And this mass over here has a mass of m1. This mass over here has a mass of m2. The universal law of gravitation tells us that the force between these two masses is going to be equal to the gravitational constant times the product of the masses. So m1 times m2, all of that over the square of the distance. Now let me be... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So m1 times m2, all of that over the square of the distance. Now let me be very clear. You might say, wait, this magenta mass right here is touching this larger mass. Isn't the distance 0? And you have to be very careful. This is the distance between their center of masses. So the center of mass of this large mass over... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Isn't the distance 0? And you have to be very careful. This is the distance between their center of masses. So the center of mass of this large mass over here is r away from this mass that's on the surface. Now with that said, let's take another example. Let's say that this large, massive star, or whatever it might be,... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So the center of mass of this large mass over here is r away from this mass that's on the surface. Now with that said, let's take another example. Let's say that this large, massive star, or whatever it might be, eventually condenses into something 1,000 times smaller. So let me draw it like this. And obviously I'm not... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So let me draw it like this. And obviously I'm not drawing it to scale. So let's say we have another case like this. And I'm not drawing it to scale. So this object, maybe it's the same object, or maybe it's a different object, that has the exact same mass as this larger object, but now it has a much smaller radius. It... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
And I'm not drawing it to scale. So this object, maybe it's the same object, or maybe it's a different object, that has the exact same mass as this larger object, but now it has a much smaller radius. It now has a much smaller radius. So that radius now, the radius is 1 over, let's just say it's 1,000th of this radius ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So that radius now, the radius is 1 over, let's just say it's 1,000th of this radius over here. So it's 1, maybe I'll just call it r over 1,000. So if this had a million kilometer radius, so that would make it roughly about twice the radius of the sun. If this was a million kilometer radius right over here, this would ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
If this was a million kilometer radius right over here, this would be 1,000 kilometer radius. So maybe we're talking about something that's approaching a neutron star. But we don't have to think about what it actually is. Let's just think about the thought experiment here. So let's say I have this thing over here. And ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Let's just think about the thought experiment here. So let's say I have this thing over here. And let's say I have something on the surface of this. So let's say I have that same mass, it's on the surface of this thing. So this is m2 right over here. So what is going to be the force between these two masses? How strong... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So let's say I have that same mass, it's on the surface of this thing. So this is m2 right over here. So what is going to be the force between these two masses? How strong are they going to want to, what's the force pulling them together? So let's just do the universal law of gravitation again. The force, let's just ca... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
How strong are they going to want to, what's the force pulling them together? So let's just do the universal law of gravitation again. The force, let's just call this force 1, and let's call this force 2. Once again, it's going to be the gravitational constant times the product of their masses. So the big m1 times the ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Once again, it's going to be the gravitational constant times the product of their masses. So the big m1 times the smaller mass, m2, all of that over this distance squared, this radius squared. Remember, it's the distance to the center of masses. This center of mass here, we're considering m2 to kind of be just a point... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
This center of mass here, we're considering m2 to kind of be just a point mass right over there. So what's the radius squared? It's going to be r over 1,000 squared. Or if we simplify this, what will this be? This is the same thing, and I'll just write it in one color just because it takes less time. Gravitational cons... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Or if we simplify this, what will this be? This is the same thing, and I'll just write it in one color just because it takes less time. Gravitational constant m1, m2 over r squared over 1,000 squared, or over 1 million. Over 1 million. That's just 1,000 squared. Or we can multiply the numerator and the denominator by a... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Over 1 million. That's just 1,000 squared. Or we can multiply the numerator and the denominator by a million, and this is going to be equal to 1 million, I'm going to write it out, 1 million, let me scroll to the right a little bit, times the gravitational constant times m1, m2, all of that over r squared. Now what is ... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
Now what is this thing right over here? That's the same thing as this F1. So this is going to be 1 million times F1. So even though the masses involved are the same, this yellow object right here is the same mass as this larger object over here. It's able to exert a million times the gravitational force on this point m... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So even though the masses involved are the same, this yellow object right here is the same mass as this larger object over here. It's able to exert a million times the gravitational force on this point mass, and actually vice versa. They're both being attracted. They're both exerting this on each other. And the reality... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
They're both exerting this on each other. And the reality is, is because this thing is smaller, because this m1 on the right here, this one I'm coloring in, because this one is smaller and denser, this particle is able to get closer to its center of mass. Now you might be saying, OK, well I can buy that. This just come... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
This just comes straight from the universal law of gravitation. But wouldn't something closer to this center of mass experience that same thing? If this was a star, wouldn't photons that are over here, wouldn't this experience the same force? If this distance right here is r over 1,000, wouldn't some photon here, or at... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
If this distance right here is r over 1,000, wouldn't some photon here, or atom here, or molecule, or whatever it's over here, wouldn't that experience the same force, this million times the force as this thing? And you've got to remember, all of a sudden when this thing is inside of this larger mass, what's happening?... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
It's no longer pulling it in that inward direction. You now have all of this mass over here. Let me think of the best way of doing it. So you could think of it all of this mass over here is pulling it in an outward direction. It's not telling you what that mass out there is doing, since that mass itself is being pulled... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So you could think of it all of this mass over here is pulling it in an outward direction. It's not telling you what that mass out there is doing, since that mass itself is being pulled inward. It is pushing down on this. It is exerting pressure on that point. But the actual gravitational force that that point is exper... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
It is exerting pressure on that point. But the actual gravitational force that that point is experiencing is actually going to be less. It's actually going to be mitigated by the fact that there's so much mass over here pulling in the other direction. And so you can imagine if you were in the center of a really massive... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
And so you can imagine if you were in the center of a really massive object, there would be no net gravitational force being pulled on you, because you're at its center of mass. The rest of the mass is outward. So at every point, it will be pulling you outward. And so that's why if you were to enter the core of a star,... | Why gravity gets so strong near dense objects Cosmology & Astronomy Khan Academy.mp3 |
So we're all familiar with what a meter looks like. The average adult male is a little under 2 meters. If you were to divide a meter into a thousand units, you would get a millimeter. I think we probably know what a millimeter is if you've ever looked at a meter stick. It's the smallest measurement on that meter stick.... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
I think we probably know what a millimeter is if you've ever looked at a meter stick. It's the smallest measurement on that meter stick. So it's already pretty hard to look at. If you were to divide each of those millimeters into a thousand sections, you'd get a micrometer. Or another way to think about a micrometer is... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
If you were to divide each of those millimeters into a thousand sections, you'd get a micrometer. Or another way to think about a micrometer is it's one millionth of a meter. So this is kind of beyond what we're capable of really perceiving. If you were to take each of those micrometers and divide them into a thousand ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
If you were to take each of those micrometers and divide them into a thousand sections, you would get a nanometer. So now we're at one billionth of a meter. You divide that by a thousand. You get a picometer. So a picometer is one thousand billionth of a meter. Or you could say a trillionth of a meter. You divide one o... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
You get a picometer. So a picometer is one thousand billionth of a meter. Or you could say a trillionth of a meter. You divide one of those by a thousand and you would get a femtometer. So these are unimaginably small things. Now once you're familiar with the units, let's explore what types of things we can expect to f... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
You divide one of those by a thousand and you would get a femtometer. So these are unimaginably small things. Now once you're familiar with the units, let's explore what types of things we can expect to find at these different scales. I'll start over here, and I've written them on the left as well, but it's more compel... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
I'll start over here, and I've written them on the left as well, but it's more compelling when you see the pictures. We'll start over here with the b. I've arbitrarily picked something of this scale. There's many, many, many, almost an infinite number of things I could have picked at this scale. But the average b is ab... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But the average b is about two centimeters long. This b right over here. It's about, give or take, one hundredth the length of the average adult human being. But once again, a honey bee, not too exciting, although it is pretty exciting to see it zoomed in like this. But a honey bee is something that we can relate to. W... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But once again, a honey bee, not too exciting, although it is pretty exciting to see it zoomed in like this. But a honey bee is something that we can relate to. We've all seen honey bees. Now, what I want to do is zoom in or look at something that's fifty times smaller than a honey bee. So something that if I were to k... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Now, what I want to do is zoom in or look at something that's fifty times smaller than a honey bee. So something that if I were to kind of show how big it is relative to this honey bee, it would look something like this. I'm doing it very rough. And that is a dust mite. And this right here, these are both pictures of d... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
And that is a dust mite. And this right here, these are both pictures of dust mites. Now, dust mites look like these strange and alien creatures. But what's amazing about them is that they are everywhere. They're all around us. You probably have many of them lying on your skin or wherever right now, which is kind of a ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But what's amazing about them is that they are everywhere. They're all around us. You probably have many of them lying on your skin or wherever right now, which is kind of a creepy idea. But we're talking about scale here. And the average dust mite, so we were talking about centimeters before. Now we'll talk about mill... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But we're talking about scale here. And the average dust mite, so we were talking about centimeters before. Now we'll talk about millimeters. The average dust mite is less than half of a millimeter. Or if you want to talk in micrometers, it's about 400 micrometers long. So this length right over here is about 400 micro... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
The average dust mite is less than half of a millimeter. Or if you want to talk in micrometers, it's about 400 micrometers long. So this length right over here is about 400 micrometers, so about 150th the length. Remember, this huge thing that I'm showing right here, this is a honey bee. It's about 150th the length of ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Remember, this huge thing that I'm showing right here, this is a honey bee. It's about 150th the length of a honey bee. Or maybe to put it in other terms that you might be familiar with, this is a zoomed in picture of human hair. And you might say, oh my god, this person has horrible hair. But no, if you were to look a... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
And you might say, oh my god, this person has horrible hair. But no, if you were to look at your own hair under an electron microscope, you'd be lucky if it looked this good. This person actually I've seen pictures of more damaged hair than this. This is probably smooth and silky hair right here. But the diameter of hu... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
This is probably smooth and silky hair right here. But the diameter of human hair, and this is on average. It depends on whose hair you're talking about. The diameter of human hair is about 100 micrometers thick. That's the diameter. So it's about a fourth the length of a dust mite. Or if I were to draw some human hair... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
The diameter of human hair is about 100 micrometers thick. That's the diameter. So it's about a fourth the length of a dust mite. Or if I were to draw some human hair relative to this honey bee, it would look something like this. And I'm drawing the whole hair, so its width would be the width of this thing that I just ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Or if I were to draw some human hair relative to this honey bee, it would look something like this. And I'm drawing the whole hair, so its width would be the width of this thing that I just drew. Remember, we're looking at a honey bee here. It looks like some type of giant, but it is a honey bee. Let's zoom in even mor... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
It looks like some type of giant, but it is a honey bee. Let's zoom in even more. So we started with the honey bee. We zoomed in by 50 to get the dust mite. We zoomed in by another factor of 4 to get the width of human hair. If we zoom in, we're in the micrometer range now. If we zoom in by roughly another factor of 10... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
We zoomed in by 50 to get the dust mite. We zoomed in by another factor of 4 to get the width of human hair. If we zoom in, we're in the micrometer range now. If we zoom in by roughly another factor of 10, we get to the scale of cells. And this right here is a red blood cell. I think this is a white blood cell right ov... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
If we zoom in by roughly another factor of 10, we get to the scale of cells. And this right here is a red blood cell. I think this is a white blood cell right over here. About 6 to 8 micrometers. So once again, if I were to draw a cell relative to this human hair, it would probably look something like this. Something o... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
About 6 to 8 micrometers. So once again, if I were to draw a cell relative to this human hair, it would probably look something like this. Something on a similar scale that we can still kind of relate to is the width of spider silk. It's about 3 to 8 micrometers. So if I were to draw some spider silk on the same diagra... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
It's about 3 to 8 micrometers. So if I were to draw some spider silk on the same diagram, it would look something like this. This is an actual image of spider silk. So once again, something that we can kind of perceive. You can bump into it. You can touch spider silk. You can see it if the sun is reflecting just right ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
So once again, something that we can kind of perceive. You can bump into it. You can touch spider silk. You can see it if the sun is reflecting just right or if it has a little bit of moisture on it. But it's about the thinnest thing that humans can perceive. And this is in the ones of micrometer range. At that same ra... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
You can see it if the sun is reflecting just right or if it has a little bit of moisture on it. But it's about the thinnest thing that humans can perceive. And this is in the ones of micrometer range. At that same range, you start to have some of your larger bacteria. Bacteria can be anywhere from, and I'm speaking ver... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
At that same range, you start to have some of your larger bacteria. Bacteria can be anywhere from, and I'm speaking very roughly, 1 to 10 micrometers. So in general, they're smaller than cells. Most bacteria are smaller than most cells. And just to figure out where we sit on our scale, have it over here. So we started ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Most bacteria are smaller than most cells. And just to figure out where we sit on our scale, have it over here. So we started off, I want to keep reminding ourselves, humans, you divide by 100, you get to the B. So each of these slashes right here are dividing by 10. So this is divide by 10. Divide by 10 again, you're ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
So each of these slashes right here are dividing by 10. So this is divide by 10. Divide by 10 again, you're divided in size by 100. Divide by 10 again, you get to millimeter. You've divided by 1,000. Divide by 10 again, you are doing tenths of millimeters, which is about the size of the human hair. You divide again by ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Divide by 10 again, you get to millimeter. You've divided by 1,000. Divide by 10 again, you are doing tenths of millimeters, which is about the size of the human hair. You divide again by 10, you're going into tens of micrometers. By 10 again, you get into the micrometer range. So now we're talking about cells, we're t... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
You divide again by 10, you're going into tens of micrometers. By 10 again, you get into the micrometer range. So now we're talking about cells, we're talking about bacteria. Now things are going to get really crazy. This was in the ones of micrometer range. Now we're going to start getting into the hundreds of nanomet... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Now things are going to get really crazy. This was in the ones of micrometer range. Now we're going to start getting into the hundreds of nanometer range. Just to get a sense of things. So remember, a nanometer is a thousandth of a micrometer. Or 100 nanometers would be a tenth of a micrometer. And this picture right h... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Just to get a sense of things. So remember, a nanometer is a thousandth of a micrometer. Or 100 nanometers would be a tenth of a micrometer. And this picture right here, this big, enormous planet or asteroid looking thing, this is a white blood cell. The enormous blue thing in this picture. And so if I were to zoom out... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
And this picture right here, this big, enormous planet or asteroid looking thing, this is a white blood cell. The enormous blue thing in this picture. And so if I were to zoom out, it might look something like this right over here. But what's really fascinating about this picture for multiple reasons are these little g... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But what's really fascinating about this picture for multiple reasons are these little green things that are emerging, that are essentially reproducing, emerging from the surface of this white blood cell. And these things right here, these are AIDS viruses. So now if we zoom in, roughly another factor of about 100 to 1... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
And all of the genetic material necessary to replicate that virus is right inside each of these little capsids, right inside each of these little green containers. So now going back to our scale, we are down to the scale of a virus. So we're in the hundreds of nanometer range. If we divide by 10 and then divide by 10, ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
If we divide by 10 and then divide by 10, you get to the nanometer range. And right in the ones of nanometer range, you get to the width of the double helix of a DNA molecule. So this right here is, if you were to zoom in, and this is an artist's depiction of it, obviously this is not a picture, so to speak, of a DNA m... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But the width of this double helix is about 2 nanometers, or another way to think about it, about 160th the diameter of one of these viral capsids. It would have to be, because it's going to have to get all wound up and fit into one of these viral capsids. And DNA, just to make it clear, this is just the width of DNA. ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
It's much, much, much, much, much, much longer, and we can talk about that in future videos. So once again, we're at a very, very small scale. If you want to think of it in terms of meters, we're at 2 billionths of a meter. You could put 500 million of these side by side to get to a meter. Or you could even think of it... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
You could put 500 million of these side by side to get to a meter. Or you could even think of it this way. This is 2 millionths of a millimeter. So once again, super small. You could put these side by side, one DNA, another DNA. If you made them touch, you could put 500,000 next to each other in a millimeter. So this i... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
So once again, super small. You could put these side by side, one DNA, another DNA. If you made them touch, you could put 500,000 next to each other in a millimeter. So this is an unbelievably small amount of space. It's going to fit into another unit that's not kind of in the conventional prefix followed by meters, an... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
So this is an unbelievably small amount of space. It's going to fit into another unit that's not kind of in the conventional prefix followed by meters, and this is an angstrom. And 10 angstroms equal 1 nanometer. So the width of this DNA double helix would be 2 nanometers or 20 angstroms. Now, if we were to divide agai... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
So the width of this DNA double helix would be 2 nanometers or 20 angstroms. Now, if we were to divide again by 10, you get to something that's 2 angstroms or 0.2 nanometers wide, and that is a water molecule. Maybe instead of using red, I should have used blue or something. But this right here is the oxygen, and it is... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But this right here is the oxygen, and it is bonded to the two hydrogens right over here. So this is beyond, frankly, human perception, or even really stuff that we can conceptualize, not to even speak of perception. We're still imagining how small we're dealing with right over here. Remember, we're dealing with less t... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
Remember, we're dealing with less than a fifth of a billionth of a meter, or a fifth of a millionth of a millimeter, something that I really can't fathom. But we're going to get even smaller than that. If we were to zoom in on one of these hydrogen atoms, and now things start to get kind of abstract, and we start deali... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But if we try our best to do it, if we were to zoom in and we were to put some boundary on a hydrogen atom, because the electrons actually could jump around anywhere, but if we set some boundary of where the electrons are most likely to be found, the diameter of a hydrogen atom is roughly one angstrom, which makes sens... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
But what's crazier than that is that it's mostly free space. We've gotten this small. We're trying to get to these fundamental units, and this thing right here is mostly free space. And that's because if you look at an electron, and when we say radius here, it's really hard to define where it starts and ends, and you h... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
And that's because if you look at an electron, and when we say radius here, it's really hard to define where it starts and ends, and you have to do some things related to the charge, and we're not even thinking about quantum effects and all of that. An electron has a radius of 3 times 10 to the negative 5th angstroms, ... | Scale of the small Scale of the universe Cosmology & Astronomy Khan Academy (2).mp3 |
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