Things You Thought You Knew – Faster Than Light

What’s up with the fourth dimension? Can anything travel faster than light? Neil deGrasse Tyson and Chuck Nice explore things you thought you knew about dimensions, tachyons, and isotopes.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Neil deGrasse Tyson?

  Coming up on StarTalk, we've got another Things You Thought You Knew episode. This time, we talk about dimensions, isotopes, and tachyons. Check it out.

• 0:13Neil deGrasse Tyson?

  Welcome to StarTalk, your place in the universe where science and pop culture collide.

• 0:22Neil deGrasse Tyson?

  StarTalk begins right now.

• 0:29Neil deGrasse Tyson?

  So Chuck, here's a topic I don't think we talk enough about: dimensions.

• 0:33Chuck Nice?

  Dementia, huh?

• 0:34Neil deGrasse Tyson?

  No, no. I can say to you, Chuck, I'll meet you tomorrow at Starbucks.

• 0:39Chuck Nice?

  Right.

• 0:40Neil deGrasse Tyson?

  And what's your reply to me?

• 0:41Chuck Nice?

  I'll be there all day waiting, man, because I've got nothing to do. I've got nothing to do. So I'll just be at Starbucks. I'll start off in the morning with some breakfast, maybe a little muffin, and then I'll just stay there until you get there.

• 0:54Neil deGrasse Tyson?

  Okay, sorry. I'll meet you at Starbucks at 12 noon, okay?

• 0:57Chuck Nice?

  Oh, thanks, thanks. I appreciate that.

• 1:00Neil deGrasse Tyson?

  I gave you a location in space, and you had to wait until I gave you a location in time.

• 1:06Chuck Nice?

  Time, right.

• 1:07Neil deGrasse Tyson?

  And that intersection of space and time is called your world line.

• 1:11Chuck Nice?

  Whoa, love it.

• 1:13Neil deGrasse Tyson?

  It's called a world line.

• 1:14Chuck Nice?

  World line.

• 1:15Neil deGrasse Tyson?

  So for our world lines to intersect, we have to be at the same place at the same time.

• 1:22Chuck Nice?

  See, now, fellas, if you're smart and you're single, you will hold this one in the back, put it away in your back pocket.

• 1:28Neil deGrasse Tyson?

  Okay.

• 1:29Chuck Nice?

  Girl, I just need you as a part of my world line, you know?

• 1:33Neil deGrasse Tyson?

  Rap lines from Relativity, right?

• 1:37Chuck Nice?

  Exactly.

• 1:37Neil deGrasse Tyson?

  Okay, and let's reverse that. I'll say, Chuck, I'll meet you tomorrow at noon.

• 1:41Chuck Nice?

  North America, good for you.

• 1:43Neil deGrasse Tyson?

  Thank you, Earth. Yeah, Earth.

• 1:45Chuck Nice?

  Is that all right?

• 1:46Neil deGrasse Tyson?

  Yeah. So we know intuitively you need both the time and the space coordinates conjoined in order to actually meet. Absurd variance in that would be you cross the street, and 10 minutes later, a truck barrels through in that same location.

• 2:03Chuck Nice?

  Right.

• 2:04Neil deGrasse Tyson?

  So you are in the same location as the truck. But not at the same time. You wouldn't say, oh, man, I almost died today. You wouldn't, because your world lines missed each other. Right. And you can do that another way. You exist at the same time as the truck, but you know we're near each other in location. Right. So what made Zoom and other video conferencing so useful during COVID is that you only had to be at the same time. Right. You didn't have to be at the same place. So you take away one of the components of the world lines. Right.

• 2:47Neil deGrasse Tyson?

  And then many more people can participate. But you are converging at the same place, virtually or digitally, so.

• 2:58Neil deGrasse Tyson?

  Uh, okay, well, your image is on, I mean, I have my image of you on my computer, but it's not you. That, this is. So let's keep talking about dimensions, ready? So we have one dimension, which is just a line. The measure of the line is the length. There's no other measurement you can make of it that has any meaning. Right. Right, it does not have a width. Now you can add another dimension, that, we call that X. We add a Y. Mm hmm. And now you have a surface. A plane. A plane, and that is two dimensions, X and Y. Okay, so you can make a square out of that, couldn't you? Yeah.

• 3:37Neil deGrasse Tyson?

  Two dimensional beings who live in that surface to everyone else in that surface, they only have an outer perimeter. Right. You can't see inside their bodies. They're all inside the flat plane. They're inside the flat. That's all they can see. All you see is the edge of them. Right, the edge. So medical surgery in a two dimensional universe, they'd have to cut you open, part you, and then reach in and do what they need to, come out and then stitch you up again. Okay? Right. If we live in three dimensions.

• 4:16Neil deGrasse Tyson?

  You get to look down on that flat world and see all the inner guts of every living creature in that universe. Because there is no boundary above and below, it's only within the plane itself. You can see the heart beating, you can see the spleen, the liver, the pancreas, the lungs. You can see it all. In fact, if you wanted to be a surgeon for that world, you could go in, cut out the appendix if they needed appendectomy, and never have to cut through their outer boundary. You'd be like magically going into their body.

• 5:00Chuck Nice?

  Dimensional surgery.

• 5:01Neil deGrasse Tyson?

  Dimensional surgery. They would have no access or even awareness that that was even possible, but you do.

• 5:09Chuck Nice?

  Right.

• 5:09Neil deGrasse Tyson?

  And you can go in and rectify that. So now, we are in three dimensions. We reveal our skin in all directions to the other people.

• 5:19Chuck Nice?

  Right.

• 5:19Neil deGrasse Tyson?

  So our skin is the boundary between our innards and a medical doctor. If they want to get inside you, they gotta cut you open.

• 5:28Chuck Nice?

  Right.

• 5:29Neil deGrasse Tyson?

  A four-dimensional creature can just look inside our bodies.

• 5:35Chuck Nice?

  Oh, I feel violated.

• 5:36Neil deGrasse Tyson?

  I know.

• 5:39Chuck Nice?

  I hope no one's watching right now.

• 5:43Chuck Nice?

  God.

• 5:44Neil deGrasse Tyson?

  Anyone from the fourth spatial dimension has full access to your entire body's innards.

• 5:50Chuck Nice?

  Oh.

• 5:50Neil deGrasse Tyson?

  They could pull stuff out, put stuff in, operate, whatever.

• 5:54Chuck Nice?

  We are the game operation to anybody in the fourth dimension.

• 6:00Neil deGrasse Tyson?

  What I'm saying is, if you had what you beautifully refer to as dimensional surgery, you would be able to operate without ever cutting someone open, provided you come from a higher dimension inward.

• 6:13Chuck Nice?

  Right.

• 6:13Neil deGrasse Tyson?

  And it is completely analogous to be a four-dimensional surgeon operating on us without cutting us open, to be we as three-dimensional surgeons operating on two-dimensional creatures, because you could just see all their organs just sitting there. Now, we can move forward and back, left and right, up and down. Okay?

• 6:34Neil deGrasse Tyson?

  Those are the three spatial dimensions, but the time dimension, you don't have access to the past or the future. We are prisoners of the present, forever transitioning between our inaccessible past and our unknowable future. But let's think this through. How would you imprison a two dimensional creature? Draw a line. What kind of line? A square. A square, just draw a square. That's its prison cell. Yeah. But we say, wait, just step up out of it and then you escape. Good to go. I don't know what you're talking about. I'm fully locked in. Fully locked in. How do we put us in a cell? We have six walls. Right. A ceiling floor, four walls around us. Right. We think we are completely contained within it.

• 7:19Neil deGrasse Tyson?

  A higher dimensional creature says, just step out and then step back in and you're outside the cell. We said, I don't know what you're talking about. Right. Wait a minute. I said a four dimensional creature. If, if we had access to the fourth dimension, which for us is what? Time. Time, but wait, we're prisoners of time. So suppose we weren't prisoners of time. Suppose you could move through time the way we move through space. Could you then escape the prison? Yeah, just move to a time when I'm not in prison. Exactly. Just say, let me get out of these six walls here. You just go back to a time before you got put in a prison or go to the future where you would let go from the prison. Right.

• 8:02Neil deGrasse Tyson?

  Each of those counts as escaping the prison without ever breaking down the wall. Right. So time can serve that same role if you had access to the past and to the future. That's pretty cool, man. Of course, we go higher this fifth dimension, six dimensions, this sort of thing. And mathematically, you can calculate what all the properties are. And it's fascinating to watch. I, I know the quick one, you ready? Go ahead. Knots in strings only exist in three dimensions.

• 8:38Neil deGrasse Tyson?

  Okay. In other words, in a fourth dimension, you hand them a knot in the fourth dimension and say, wait, just, just pull the ends. Right. And it unravels itself. That's the same thing as we three dimensional people looking at two dimensional people. And they have a string that just has this loop in it. One loop. Right. And they say, how do I untie this? I can't untie. Say, don't pick up the two ends and stretch. They can't do that. Right. They can't do that. So knots are different things in higher dimensions. The way to do it is you have to make a knot out of a two dimensional ribbon. And there are ways to do that, I think, and rather than just out of a string.

• 9:19Neil deGrasse Tyson?

  So a lot of interesting things change and are mind boggling for ascending to a higher dimension. Sweet. One last quick thing. Mm hmm. Why does anyone want a flying car? So you can get up and over traffic. So you only really think about flying cars in cities where you're like plugged with traffic. And what a flying car gets you is another dimension of travel. True. You know, when I'm stuck in a one lane road, because that's bad, all right? But even if you go two dimensions and you have multiple lanes, because now you're in a plane, that can get cloggy too. Right. So get a third dimension is wide open. But wait a minute. That means we already have flying cars.

• 10:06Neil deGrasse Tyson?

  It's called the subway. Ooh. Instead of being in the air, it's underground, bypassing the traffic you're in. It still invoked the third dimension.

• 10:17Neil deGrasse Tyson?

  But also, it means overpasses, where the freeway goes right through and the overpass goes, oh, that's a flying car right there. You invoked another dimension. You have a very low bar for what's called flying.

• 10:46Speaker 02

  I'm Joel Cherico and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 11:02Neil deGrasse Tyson?

  Chuck.

• 11:03Chuck Nice?

  Yeah.

• 11:03Neil deGrasse Tyson?

  Have you ever wanted to travel faster than light?

• 11:06Chuck Nice?

  Sure. I mean, who doesn't? I mean, I spent countless hours just sitting around saying to myself, I wish I could go to like Proxima B and just float above it and be there.

• 11:18Neil deGrasse Tyson?

  You may know that Voyager 1 is the fastest thing we've ever sent out of the solar system.

• 11:25Chuck Nice?

  Right.

• 11:25Neil deGrasse Tyson?

  If we had aimed that towards Alpha Centauri.

• 11:29Chuck Nice?

  Uh huh.

• 11:30Neil deGrasse Tyson?

  The star system that contains Proxima, this very closest star to the sun.

• 11:34Chuck Nice?

  Right.

• 11:35Neil deGrasse Tyson?

  You would get there in plus or minus a few months, 70,000 years.

• 11:43Neil deGrasse Tyson?

  But even if you went there at the speed of light, we would watch you take four years. Your time would stop.

• 11:48Chuck Nice?

  Right.

• 11:49Neil deGrasse Tyson?

  So you would get there instantly, but you want to cross the galaxy. That's 100,000 years, Earth time for you to do that. So we need other ways to travel experimentally and theoretically that you cannot travel faster than light.

• 12:01Chuck Nice?

  Right.

• 12:02Neil deGrasse Tyson?

  Through space.

• 12:03Chuck Nice?

  Right.

• 12:03Neil deGrasse Tyson?

  However, some decades ago, someone hypothesized, suppose you don't increase your speed to try to get to the speed of light. Suppose you exist on the other side of that boundary. You just start life on the other side of that boundary. What would that be? What does that even mean? Okay. So if you look at the equations of relativity, there are three things that happen as you travel faster. Your time slows down as you near the speed of light.

• 12:37Chuck Nice?

  Right.

• 12:38Neil deGrasse Tyson?

  Your length shortens.

• 12:40Chuck Nice?

  Okay.

• 12:40Neil deGrasse Tyson?

  In the direction of your motion and your, your mass increases.

• 12:45Chuck Nice?

  Okay.

• 12:46Neil deGrasse Tyson?

  If you try to get to the speed of light as a physical object, your length shortens to zero, your mass, mass goes to infinity.

• 12:57Neil deGrasse Tyson?

  And time stops. Okay, this is just insane. This is insane because the equations blow up there.

• 13:03Chuck Nice?

  That's the numbers, right?

• 13:04Neil deGrasse Tyson?

  Okay, the numbers give you.

• 13:05Chuck Nice?

  All right.

• 13:05Neil deGrasse Tyson?

  So it was hypothesized, suppose you come at it from the other side.

• 13:12Neil deGrasse Tyson?

  So you're not working your way towards the speed of light. You just exist with speeds that are already faster than the speed of light. So you don't have this violation of approaching the speed of light itself.

• 13:23Chuck Nice?

  Okay.

• 13:25Neil deGrasse Tyson?

  When you do that, what comes out the other side is that you live backwards in time.

• 13:34Chuck Nice?

  Oh, that's a Benjamin Button.

• 13:36Neil deGrasse Tyson?

  Okay, so it's not just that, you know, time slows down. Time now goes backwards. A, B, the slowest you can travel is the speed of light.

• 13:47Chuck Nice?

  Right.

• 13:48Neil deGrasse Tyson?

  And in fact, it would take infinite energy to slow you down to that speed.

• 13:52Chuck Nice?

  Right.

• 13:53Neil deGrasse Tyson?

  In the same way, it would take infinite energy to speed on this side of that universe.

• 13:57Chuck Nice?

  To speed you up.

• 13:58Neil deGrasse Tyson?

  Speed you up to that speed.

• 14:01Chuck Nice?

  Right.

• 14:01Neil deGrasse Tyson?

  So someone said, could anything exist there? And so we came up with, we, people decades ago, came up with the name tachyon.

• 14:09Chuck Nice?

  And that's because they dress poorly.

• 14:11Neil deGrasse Tyson?

  Tachyon.

• 14:12Chuck Nice?

  They just mix of stripes and polka dots and all kinds of madness.

• 14:17Neil deGrasse Tyson?

  Electrons or protons, they're badass.

• 14:19Chuck Nice?

  Electrons or protons, they GQ to the max.

• 14:23Neil deGrasse Tyson?

  Tachyons don't invite them.

• 14:26Neil deGrasse Tyson?

  Plus they'll come late, or they'll come early.

• 14:29Chuck Nice?

  They don't even know when to show up.

• 14:32Chuck Nice?

  You know, what are you all? I'm on tachyon time, brother.

• 14:35Neil deGrasse Tyson?

  Tachyons from the Greek is a word for speed.

• 14:38Chuck Nice?

  Okay.

• 14:38Neil deGrasse Tyson?

  So tachyons, the slowest they can go is the speed of light and the fastest they can go is infinite speed.

• 14:44Chuck Nice?

  Right, yeah.

• 14:45Neil deGrasse Tyson?

  So in that case, you can go any distance.

• 14:47Chuck Nice?

  You can go any distance you want.

• 14:48Neil deGrasse Tyson?

  Any amount of time.

• 14:48Chuck Nice?

  Right, because at that point, you don't need a warp engine, you need a tachyon engine.

• 14:52Neil deGrasse Tyson?

  You need a tachyon, tachyon.

• 14:53Chuck Nice?

  A propulsion.

• 14:54Neil deGrasse Tyson?

  A tachyon chariot to carry you through the galaxy.

• 14:57Chuck Nice?

  Look at that. Well, you made it very poetic and it's the vehicle of the Greek gods.

• 15:02Neil deGrasse Tyson?

  Here's an interesting fact, that the early universe expanded faster than the speed of light.

• 15:08Chuck Nice?

  Right.

• 15:09Neil deGrasse Tyson?

  Okay, now, the way that happened was.

• 15:13Neil deGrasse Tyson?

  The space itself is expanding. Right. Nothing is moving through. Nothing's moving through space. Right. Right. Space is no longer a medium. It's the actual vehicle. But medium through which you're moving, it is the thing itself. It's the thing that's moving. There's no, that's, there's no violation of the speed of light there. And we learned that from the general theory of relativity, which generalizes all of the parameters for which there were very specific descriptions in the special theory of relativity. Right. In other words, the special theory of relativity involve a constant motion with no acceleration. So it was a simplified case. Uh, if we can call relativity simple at all, the simplified case, the general relativity involves accelerations and gravity and curved spacetime and all the rest of this. Right.

• 15:58Neil deGrasse Tyson?

  When you learn about space and time as a fabric of the universe, it can stretch at any speed at all. And the early universe stretches faster than light. So that's where that's coming in. Right. In case there was a question about it. Yeah. But now, it turns out you can travel faster than light in a medium where light travels with a lower speed than it would in a vacuum. Okay. So like water going, like water. Water, light going through water, light going through glass, light going through diamond, all travel slower than light going through a vacuum. Got you. Those lower speeds, hey, we can go fa- we know how to send particles faster than those speeds.

• 16:43Neil deGrasse Tyson?

  We do that all the time. When we accelerate electrons and protons and particle accelerator. So in a diamond, light travels forty percent as fast as it does in empty space. Wow. If light were sixty, sixty miles an hour, in a diamond, light's going twenty-four miles an hour. Right. So what happens now if we send a particle faster than light in the medium?

• 17:09Neil deGrasse Tyson?

  We didn't know and it was tested and we found out that when that happens. The whole universe explodes. Everything disintegrates like a Thanos snap.

• 17:23Neil deGrasse Tyson?

  So you have water and so now you take a particle and accelerate it not only to the speed of light in water but exceeding it and when that happens there's a flash of light and it's called in that case Shrenkov radiation. Shrenkov radiation. The speed of light would be faster in air but still slower than the vacuum of space. So air is less dense, the water is less dense than diamond. Okay. So we're getting slow light when it hits our atmosphere and comes down to us. It's already slowed down. It's already slowed down. It's already slowed down. So it bends in the atmosphere and then it bends again going into the water. If you have a diamond ring underwater, it bends going into the diamond ring. Wow. So you got to, you know, get a four bend path on that.

• 18:06Neil deGrasse Tyson?

  So my point is going faster than light triggers this reaction between the charged particle, electron and proton and the medium and flashes of blue light come out. It's called Shrenkov radiation. It's just Shrenkov light, uh, just to be simple. All light is radiation. Exactly. People say it was radiation, oh my God. But it, um. Yeah, you're being bombarded with radiation every single day, all day. Correct. It's just low energy radiation. Your arms don't fall off, right? Okay. High energy radiation that is ionizing, that's bad for you. Low energy radiation, it makes no difference to your body. Body doesn't care. Exactly. So this thing about going faster than light and then emitting this energy is kind

• 18:51Neil deGrasse Tyson?

  of like a sonic boom, right? I mean, it's, it's conceptually similar. You go faster than sound in the medium, then there's this shockwave that comes out upon doing so. So think of it as kind of a light shockwave. Oh, that's pretty cool. You know what will just bypass tachyons? What's that? Wormholes. Of course, yes. Yeah, wormholes, you don't need rockets. You don't need transporters like what they have on Star Trek. Right. Just open a portal, step through, you're there. There you go. You don't have to be dematerialized, beamed, and then re-materialized on the other side. All right. And not only that, that material, I think, only goes at the speed of light. It's still limited by the speed of light, even when they do beam. Right. All right, that's all I got for you. All right.

• 19:36Neil deGrasse Tyson?

  This is the most time we've ever spent about talking about something that we don't know exists. That we don't know exists. That's, that's pretty cool. There it is.

• 20:07Neil deGrasse Tyson?

  There's a word, a subject, a topic of interest that I think people don't know as much about as they should. Okay. It's all about isotopes. There's a sequence of elements, beginning with hydrogen, and they get sort of heavier and heavier and heavier. Right. And they each have a number. So hydrogen is number one, helium is number two. So we're not just numbering them. That is the count of protons in their nucleus. Right. Who's got 12 protons? Who's got six protons? There is an element, and only one element, that has that many protons in the nucleus. There you go. Some famous ones, carbon has six protons. Six protons.

• 20:49Neil deGrasse Tyson?

  Oxygen has eight protons. I left one out. Nitrogen has seven protons. Okay. Uranium has 92 protons. Okay. When the periodic table of elements was being discovered, there were gaps. So you knew exactly what to look for if you were missing an element. Look for the one with 39 protons. Go, go back to the lab. It's like a, a chemical Lego set.

• 21:19Neil deGrasse Tyson?

  You just put it in a slot, clicks right in and you move on. And so we have found 92, quote, "natural elements" in the universe, 1 through 92. Hydrogen right on up through uranium. And we have another, how many, up to 118 now, going beyond uranium. We made those in the laboratory.

• 21:44Chuck Nice?

  You think you can play God, sir? Is that so? You're just making elements now?

• 21:51Neil deGrasse Tyson?

  The answer is frankly, yes.

• 21:53Chuck Nice?

  There you go.

• 21:54Neil deGrasse Tyson?

  So these are the protons and they're immutable. What I mean is if you take away a proton, it's no longer that element, it's the other element.

• 22:02Chuck Nice?

  Right.

• 22:03Neil deGrasse Tyson?

  If you add a proton, it's now a different element. Wait a minute, protons all have the same charge.

• 22:12Neil deGrasse Tyson?

  They all have positive charge. So what does it mean to cram them into the nucleus of an atom? If left to their own devices, they would what?

• 22:22Chuck Nice?

  Oh, man, they, you know, it's, they'd be the Real Housewives of New Jersey. That's what, that's what they'd be.

• 22:36Neil deGrasse Tyson?

  So what holds them together? Well, there's a whole other force of nature called the strong force.

• 22:41Chuck Nice?

  Fundamental force of nature?

• 22:42Neil deGrasse Tyson?

  Fundamental force of nature. And it's propagated by a particle called the gluon.

• 22:47Chuck Nice?

  Right.

• 22:47Neil deGrasse Tyson?

  Aptly named, I might add. And this happens by the presence of neutrons in the nucleus.

• 22:55Chuck Nice?

  Right.

• 22:56Neil deGrasse Tyson?

  So neutrons tamp down the resistive forces and they act as a sort of a glue for the nucleus.

• 23:05Chuck Nice?

  Unless you're a Martha Stewart atom, in which case it's a hot gluon.

• 23:11Neil deGrasse Tyson?

  That was terrible. They all can be winners, like you said. Exactly. You know, I would say Martha should not have gone to prison for that. I should have. So hydrogen in its native state only has one proton. Right. It doesn't need a neutron. Right. To hold anything together. So native hydrogen is just one proton and then one electron on the outer side. Oh, by the way, in a red blooded atom, they have as many electrons as as protons. So they're electrically neutral. Right. Okay, so uranium would have how many electrons? As many as it has neutrons. No, no, it's amazing it has protons. Protons. Protons. So how many is that? Um, I don't know. You don't remember? I said it. Ninety two.

• 23:52Neil deGrasse Tyson?

  Ninety two, exactly. So so matter is generally neutral for this reason. Okay, hydrogen is happy. Let's go to helium. Helium has two protons. Right. Its native state has two neutrons. Okay. Suppose I force hydrogen to accept a neutron and I cram it in there. Okay, I can do that. Now I have what's called heavy hydrogen. Heavy hydrogen. It has a whole word that we have for it. It's called deuterium. Oh. You might have heard the word deuterium. Do tell. What is what does deuterium do? You can make a water molecule out of deuterium. H two O. If one of those hydrogens is a deuterium,

• 24:36Neil deGrasse Tyson?

  then it's D H O. Is that heavy water? That's heavy water. Heavy. You might have heard of heavy water. Yeah. You can add two neutrons to it. Okay. We have a word for that. Obese water.

• 24:52Neil deGrasse Tyson?

  It's called tritium. Tritium. Point is, when you do this to an atom, adding neutrons, or possibly subtracting neutrons, if it has stuff it won't miss, you made an isotope. Ah. So deuterium and tritium are isotopes of hydrogen. Of hydrogen. Let's go to carbon. Carbon has six protons in the nucleus. Right. So red-blooded carbon would have how many neutrons? Uh, six. Six, and it'll have six electrons. Electrons. Carbon, bada bing, okay? Oh, wait a minute. I can add two neutrons to it. Ooh.

• 25:32Neil deGrasse Tyson?

  So now it has six protons and now eight neutrons. Add those two numbers to get, what do you get? Fourteen. Fourteen, huh? Carbon fourteen. Carbon fourteen. As in carbon fourteen dating? Yes, yes. You know, someone should make a carbon fourteen app, a dating app. That'd be, that'd be kinda cool. That'd be kinda cool. So, that's an isotope of carbon, alright? It turns out, carbon twelve is stable. Twelve is six protons, six neutrons. It's stable. Right. You add two neutrons, it's not stable. Right. It will decay. And a half-life. Yeah, a half-life. And the half-life of carbon fourteen, if I remember correctly,

• 26:15Neil deGrasse Tyson?

  it's around five thousand years, which means after that amount of time, half of the carbon fourteen is no longer there. Right. It has decayed. And then you wait another five thousand seven hundred years, half is gone again. Right. You wait another five thousand seven, it's half a half of a half is an eighth. Right. So you keep doing this, and you know what it does? It gives you access to dates across all of recent human history. From when we were in caves, up through recorded history, right on up back through a thousand years ago, five hundred years ago. So it's very useful for dating life on Earth.

• 27:00Neil deGrasse Tyson?

  Some carbon that's in your body is carbon fourteen. So how, how do we end up with the carbon fourteen in our bodies? So carbon in nature, add carbon thirteen in there too. So carbon twelve, stable. Carbon thirteen, stable, there's not much of that. Carbon fourteen, unstable. Unstable. Okay, so in the environment.

• 27:22Neil deGrasse Tyson?

  Carbon 14 would normally just disappear, except there are sources of carbon 14 from cosmic rays from space. Space rays? Space rays. Space rays. Space rays. We got space rays. Okay, you know what else boosted carbon 14 levels? What? Nuclear tests that went on in the 1950s and 60s. Ah. So here's what happens, when you are alive, you uptake that native amount of carbon 12, 13, and 14 into your body. Okay. And it stays at that level, okay, until you die, because then you stop ingesting more carbon, there's carbon in all food you eat, basically. Right. Or food that has any nutritional value, has carbon in it, okay?

• 28:05Neil deGrasse Tyson?

  The moment you die, you're no longer refreshing the carbon. And the carbon 14 then decays. And then that's when we can figure out the timing. Correct. The nuclear tests have interfered with some of the baseline measurements of what's going on in our environment. So you have to sort of get the nuclear tables together with the tables of nature in order to figure out what the starting levels were for life forms that were exposed to it. We've actually put the finger on the scale. The thumb on the scale. On the scale with the nuclear test. Yeah, with the nuclear test. Anyhow, I was just, you know, chewing the fat here with isotopes. I love it. And, you know, they're fun, other part of what's going on on the periodic table

• 28:50Neil deGrasse Tyson?

  of elements. Yes. And one other thing, hydrogen has one proton and helium, remember, has Has two. And helium in its native state has a total of four nucleons, two protons, two neutrons. Right. And it's stable. Okay. It turns out, that's called helium four, because it's got four particles in its nucleus, two protons, two neutrons, helium four. If you take away one of the neutrons. Right. Guess what you have? Um, helium 3? Yes.

• 29:21Neil deGrasse Tyson?

  Helium 3. Helium 3. Now, here's what's cool about helium 3. Helium 3 is one of the particles ejected by the sun. Right. And it gets embedded into the lunar surface. We might have talked about this in another show. So helium 3 is yet another isotope, but now that's one with one fewer neutrons instead of more neutrons. That was another installment of Things You Thought You Knew. Neil deGrasse Tyson here, as always. Keep looking up.