Cosmic Queries: Time Travel

In this Cosmic Queries episode, Neil deGrasse Tyson gets all wibbly-wobbly, timey-wimey as he answers fan questions about time travel with Colin Jost, Saturday Night Live’s new Weekend Update anchor. Image courtesy of Wikimedia Commons, Credit: aussiegall from Sydney, Australia.

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

• 0:01Neil deGrasse Tyson?

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

• 0:21Neil deGrasse Tyson?

  Welcome back to StarTalk Radio. I'm your host Neil deGrasse Tyson, astrophysicist with the American Museum of Natural History in New York City. We're going straight into time travel questions. Time travel question, I need help because these questions come to us from the internet, from Facebook and Twitter and on the phone and Google Plus. And so I combed the neighborhood and I found Colin Jost wandering. Colin, welcome to StarTalk Radio.

• 0:53Speaker 01

  Thank you very much. It's great to be here.

• 0:54Neil deGrasse Tyson?

  So you've been like a comedian your whole life. When you were a kid, did your parents say, "What are you, a comedian?" Were you one of those?

• 1:02Speaker 01

  I totally was. I was in like grade school, I was impersonating David Letterman and doing David Letterman shows.

• 1:09Neil deGrasse Tyson?

  You were the class clown.

• 1:10Speaker 01

  I was, I was, well, I wasn't like the goofy class clown. I was trying to, you know, aspiring to be the smart class clown.

• 1:17Neil deGrasse Tyson?

  The smart class clown. Good, good, good. I wonder if anyone ever thought that it would amount to anything in your life?

• 1:22Speaker 01

  I don't know.

• 1:23Neil deGrasse Tyson?

  Well, actually, has it?

• 1:25Speaker 01

  Well, that's a great first question. Enough that I'm here, I guess.

• 1:30Neil deGrasse Tyson?

  Well, welcome, welcome. You come quite pedigreed. You're a writer for Saturday Night Live. I did a little bit of homework on you, excellent. And also you do stand up and you can be found around town. And you're tweeted at TheColinJost.

• 1:45Speaker 01

  That's right, yeah.

• 1:46Neil deGrasse Tyson?

  All right, we'll be following you there. So I brought you in to just kind of cull these questions. I haven't actually seen the questions yet, but you have. And so just fire them, fire them in.

• 1:56Speaker 01

  Fire away.

• 1:57Neil deGrasse Tyson?

  I'm sitting and ready for you.

• 1:58Speaker 01

  This is great. They look really good to me. So the first one is just a pretty great question to start off time travel, which is, it's coming from Facebook, from a guy named Sean Karp on Facebook.

• 2:08Neil deGrasse Tyson?

  Sean Karp.

• 2:10Speaker 01

  And the question starts, what is time? Really nice intro. It continues, what is time?

• 2:16Neil deGrasse Tyson?

  Although, so he's not satisfied with just-

• 2:18Speaker 01

  He's not satisfied. This is not, you'll see, there's a paragraph here, so he's not satisfied with anything.

• 2:23Neil deGrasse Tyson?

  Okay, let's go.

• 2:24Speaker 01

  So, what is time? And he says, in A Sound of Thunder by Ray Bradbury, he speaks of time as a linear thing, which can be altered. However, in Star Trek, the 2009, he points out Star Trek, time is also linear, but can be diverted into parallel streams like a river or a highway. The Doctor refers to time like this. People assume-

• 2:45Neil deGrasse Tyson?

  Excuse me, Doctor as in Doctor Who? The show, Doctor, The Doctor Who, yeah, yeah.

• 2:48Speaker 01

  I'm assuming, I'm assuming, unless it's just his own personal physician launching into-

• 2:54Neil deGrasse Tyson?

  Into the metaphysics of time.

• 2:56Speaker 01

  Let me tell you about time first, you know? Uh, in the middle of a proctology exam, let me, let's talk about time for a second. The Doctor refers to time like this. People assume that time is a strict progression of cause to effect, but actually, from a nonlinear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff. And he says, are any of these explanations more true, or none even close? Other thoughts?

• 3:21Neil deGrasse Tyson?

  Well, okay, excellent. And a beautiful reference there with three sources of science fiction, including the late Ray Bradbury.

• 3:29Speaker 01

  That's right.

• 3:30Neil deGrasse Tyson?

  In fact, so, so, time, all we can tell you of time is how we measure it and what consequences different phenomenon and, uh, behavior of the universe have upon it. So, here we are, sort of progressing through time, second after second, and we're prisoners of the present, forever moving between the past and the future. That's how we think of it. However, if I set you into motion, the very clearly identified and well-tested laws of relativity tell you that I can slow down or speed up your time relative to other things around you. So, time in that sense is not linear. It can be stretched or shrunk.

• 4:14Neil deGrasse Tyson?

  Relative to other things that are around it. And not only that, in the vicinity of supermassive black holes that distort the fabric of space and time, because the fabric of the universe is not just what it does structurally to the space, it's the fabric of what the time is doing as well. So imagine two black holes ready to collide. That's an awesome disturbance in the fabric of spacetime.

• 4:42Speaker 01

  And so, a black hole is an area where the light, the energy in it is traveling faster than the speed of light?

• 4:50Neil deGrasse Tyson?

  Well, no, so, once you fall into a black hole, you never come out, not even if you are a beam of light. So, so that's why it's black, and that's why we sensibly call it a hole.

• 5:00Speaker 01

  So, if you think of like a beam of light struggling to get out of a drain, it's not even getting out?

• 5:04Neil deGrasse Tyson?

  It's not even getting out, therefore, it's black. And so, the consequence of this, it's not just simply that the light can't get out, space curves back upon itself, so that the light is trying to get out, but there is no pathway for it to occupy. And that is a severe curvature of space and time. And so, of these three definitions here, as represented in science fiction, I'd have to go with the doctor.

• 5:29Speaker 01

  All right.

• 5:30Neil deGrasse Tyson?

  And the series Doctor Who.

• 5:32Speaker 01

  Doctor Who.

• 5:33Neil deGrasse Tyson?

  Wiggly, wobbly, wimy.

• 5:37Speaker 01

  Yeah, wibbly, wobbly, timey, wimy stuff.

• 5:40Neil deGrasse Tyson?

  Yeah, it's, it's, now, about whether time can split, we simply don't know. Is there some other universe where you are left-handed and not right-handed, that's split at some point in your, I mean, we just don't know.

• 5:52Speaker 01

  Right.

• 5:52Neil deGrasse Tyson?

  We just got, we have a hard enough time trying to understand our one universe.

• 5:56Speaker 01

  Yeah.

• 5:57Neil deGrasse Tyson?

  Much less rivers that might flow from it.

• 5:59Speaker 01

  People have that, I think, that people have that fantasy of, oh, if I had another life, I would do this, and if I had another life...

• 6:04Neil deGrasse Tyson?

  And they're hoping that that life is actually going on right now.

• 6:07Speaker 01

  Somewhere, yeah.

• 6:07Neil deGrasse Tyson?

  In another universe. So, I go with the Doctor Who on that one.

• 6:10Speaker 01

  And when we were talking about black holes, so, is it, maybe this is a more elementary question, but where does all the stuff go that's getting sucked in?

• 6:18Neil deGrasse Tyson?

  Yeah, that's a, it's an elementary and extraordinarily good question. It can be both at the same time.

• 6:26Speaker 01

  In parallel worlds, I'm dumb and smart.

• 6:29Neil deGrasse Tyson?

  So, uh, every law of physics that we know says that once you fall into a black hole, you will collapse down to what we call a singularity. The, by the way, that was our word first. Uh, who's this guy who's been using it for, um?

• 6:42Speaker 01

  With cell phones with singularity like?

• 6:43Neil deGrasse Tyson?

  Yeah. So, uh, Ray Kurzweil's been using that. He stole that from us. Just let, just some telling you right now. He's saying that's the day in the future where computers get faster and computationally than the human brain. And then you can't distinguish the two and you can upload your mind into a computer and live forever. It's our word, singularity. So in the center of a black hole, all matter and energy collapsed to that infinitesimal point. And we don't know what happens at that point. Our physics ends.

• 7:12Speaker 01

  Well.

• 7:13Neil deGrasse Tyson?

  At that point. And so, uh, we need new laws of physics, like string theory and other things, but they're working on it. We've got top people working on that.

• 7:21Speaker 01

  And is there, what, is there a black hole that's anywhere near enough that even in, you know, centuries from now, we'll send something into it to find out or no?

• 7:29Neil deGrasse Tyson?

  Uh, well.

• 7:30Speaker 01

  Is that a hard?

• 7:31Neil deGrasse Tyson?

  Yeah, you wanna, you wanna go?

• 7:32Speaker 01

  Well, so I thought we'd start like the traditional way, monkey, you know?

• 7:39Neil deGrasse Tyson?

  Oh, I see. Send a, yeah, a hamster first.

• 7:41Speaker 01

  Yeah, exactly. Yeah.

• 7:43Neil deGrasse Tyson?

  Anyway, we gotta close out this segment. We'll see you after the break.

• 8:05Neil deGrasse Tyson?

  This is StarTalk Radio and we're in the Cosmic Queries part of the show. I'm your host, Neil deGrasse Tyson, and I'm with Colin Jost. Colin, welcome to StarTalk. Did I pronounce your name right?

• 8:17Speaker 01

  Colin, but Colin.

• 8:19Neil deGrasse Tyson?

  Colin Jost.

• 8:20Speaker 01

  Most people get Jost wrong, so you're, you're already ahead of the game.

• 8:22Neil deGrasse Tyson?

  No, I'm only half. Okay, because I did better than others in that and worse than the other. All right. No, that makes me dead even, I think.

• 8:30Speaker 01

  Yeah.

• 8:30Neil deGrasse Tyson?

  I got you on to just ask me these questions. You're gonna be sort of the everyman person out there.

• 8:36Speaker 01

  That's right.

• 8:36Neil deGrasse Tyson?

  Because we get questions, and for this particular show, we've culled together all the questions on time travel, because that's what this show's been about. And I've not seen these questions in advance, but you've reviewed them from Facebook and Twitter and every other way people have access to us. So, fire on.

• 8:53Speaker 01

  Oh, yeah. So, this one, this next one is from Google Plus, like, even better.

• 8:58Neil deGrasse Tyson?

  I never met Google Plus.

• 8:59Speaker 01

  Even better than Google. Just a little bit better.

• 9:01Neil deGrasse Tyson?

  So, Mr. Plus asked a question.

• 9:03Speaker 01

  A little more charged. This question comes from Frasier Cain of the website Universe Today, and it's a question I've also wondered many times. Doesn't the fact that there are no time travelers now prove that time travel will never be invented in the future?

• 9:17Neil deGrasse Tyson?

  Yeah, that's an excellent point, and I've always thought about that. Because I said to myself, in fact, if you watch the TV, the CBS sitcom, The Big Bang Theory, in the roommate contract of... I know, you gotta be totally in the show for this.

• 9:34Speaker 01

  Yeah, no, no, no.

• 9:35Neil deGrasse Tyson?

  But in the roommate contract, it stipulated that, if I'm getting the details of it wrong, the sense of it is right.

• 9:40Speaker 01

  They'll still be very excited.

• 9:42Neil deGrasse Tyson?

  If any one of them invents a time machine in the future, they have to go back to that moment that they're reading that phrase in the roommate contract to show up in the room. And so, so they're going through the contract, and then they pause for a moment. Nope, okay, we have, you know, you're not the one who invents the time machine in the future.

• 10:00Speaker 01

  That's the ultimate, like, let's agree to meet back here 10 years from now, but it's at the same time.

• 10:04Neil deGrasse Tyson?

  Exactly. And so, I think that's a, that's a pretty good argument, and I don't have a rebuttal to that.

• 10:11Speaker 01

  But, you know, what if people are hiding it? What if people have come back but are not telling people for some reason because they wanna give something away?

• 10:18Neil deGrasse Tyson?

  There's a quote, I think it was from Raoul Dahl, but others perhaps have said it, that "The only secret that can be kept between two people is when one of them is dead." So I'm pretty sure that if a time machine were out there, people would have figured that one out. It's been rumored that the, uh, the reason why the Titanic sank is because in the future they invented a time machine and everyone wanted to go back to the Titanic to see the iceberg when it hits. And then it overloaded the Titanic and it sank.

• 10:48Speaker 01

  Oh, well, now I'm convinced.

• 10:50Neil deGrasse Tyson?

  So here's the evidence. You're looking for evidence?

• 10:52Speaker 01

  There we go.

• 10:53Neil deGrasse Tyson?

  That's hardcore evidence. So, uh, that's a pretty good one.

• 10:57Speaker 01

  Yeah.

• 10:58Neil deGrasse Tyson?

  And it may, it might be that your time travel machine can only take you into the future. And then you don't have these paradoxes of killing your grandmother and then you're never born.

• 11:07Speaker 01

  Yeah, weird Back to the Future stuff.

• 11:09Neil deGrasse Tyson?

  Yeah, yeah, exactly.

• 11:10Speaker 01

  Cause there's a movie too called Looper or Loopers that with Bruce Willis and he goes back in time. He's like an assassin that goes back in time and he goes back and he's scheduled to kill himself. So he has to like figure out what to do about it.

• 11:21Neil deGrasse Tyson?

  You know what's interesting? All these TV shows, they have people going back and killing people. All you have to do, all you have to do is pick a time where two of your ancestors who mated produced one of your ancestors. And all you have to do is prevent them from mating. You don't have to kill anybody. Just, just, just your great, great, great, great, great grandparents, prevent them from mating. You would have never been born.

• 11:44Speaker 01

  Yeah, just enough with the killing.

• 11:45Neil deGrasse Tyson?

  Right, right. Forget the blood and guts. And so it doesn't take much to completely alter the path of who's alive and who was never born or who was never conceived in this world.

• 11:56Speaker 01

  Yeah. All right. Next question here comes from Facebook, Deray Pringle or Dare Pringle. And the question is, if I had a time machine like HG Wells, if I traveled back in time six months, would I not find myself floating in space with the earth on the other side of the sun? And if I was in LA and traveled back in time three hours, wouldn't I find myself roughly in New York and a few feet off the ground?

• 12:20Neil deGrasse Tyson?

  Okay. So what's going on there of course is it presumes that the time machine is only working in the time coordinate. But to quote, uh, who was it? It was not Einstein. I think it was, it'll come to me in a moment, one of the great physicists of the early twentieth century, upon realizing the implications of relativity noted that no one has ever been at a place. Without there having been a time attached to it, and no one has existed in time without being at a place. And so forever, space and time, now in our new understanding of the fabric of the universe, space and time are part of the same coordinate system.

• 13:05Neil deGrasse Tyson?

  So, an intelligently rendered time machine, and this is a very clever and perceptive point of Mr. Pringle, a clever, a properly conceived time machine would recognize, maybe it's a setting, in the settings function, your time machine. It's like, put me back in time and the same place that I am relative to everything else. But otherwise, if you're only moving back in time, you are, you're correct. You go back in time six months, you are floating in space and Earth is on the other side of the sun, and you'll, the side of you not facing the sun will freeze, and the side of you facing your sun will burn.

• 13:40Speaker 01

  Wow.

• 13:41Neil deGrasse Tyson?

  That's what happens when you're in space.

• 13:42Speaker 01

  So definitely you want to specify.

• 13:44Neil deGrasse Tyson?

  Well, you can rotate, rotisserie style, to stay warm, but then you'll just suffocate. So, you gotta specify location as well as time. Otherwise, you're, you're hosed.

• 13:53Speaker 01

  Is that when you talk about, like, when, not you, but when just one talks about time as a dimension, is that a way to think about it too, that it's almost like on an axis? And they're all one?

• 14:03Neil deGrasse Tyson?

  It is totally an axis. It's totally an axis. And so you want to choose the axis, the movement in time, back in time, so that the space carries you with the object that you care about, be it the planetary surface or whatever else you're doing. By the way, the sun is in orbit around the center of the galaxy. If you go back in time a million years, you want to make sure you were not only on Earth, but that Earth was still part of the sun, in the sun's orbit around the center of the galaxy. Not only does Earth and the moon orbit each other, Earth and the sun orbit each other, and the sun in the center of the galaxy do their dance as well. So it's quite the ballet.

• 14:38Speaker 01

  Yeah. This is a related question from Twitter from Sean Sanford. And this says, when time traveling, would one need to travel in exact one-year increments to show up at the same location on Earth?

• 14:50Neil deGrasse Tyson?

  Yeah, so if you only had the capacity to travel in time, yeah, you'd have to sort of do the one-year increment. But like I said, the sun in that one year has moved mightily in its orbit around the center of the galaxy.

• 15:01Speaker 01

  And other things have changed, obviously, relative to where you were.

• 15:03Neil deGrasse Tyson?

  Exactly. So you have to be, you have to think about that. I'm glad people are concerning themselves.

• 15:08Speaker 01

  I know. It's a very, it's a very high level of concern for time travel.

• 15:13Neil deGrasse Tyson?

  Exactly. It's a very deep, it's a much deeper...

• 15:15Speaker 01

  Than like, do I get a toothbrush? What do I, what's the situation there?

• 15:18Neil deGrasse Tyson?

  Exactly.

• 15:19Speaker 01

  Very high, high-level concerns. This next one is on Twitter. It's from Adrian Jones. And the question is, if we could fold two points of spacetime together, what would happen to the matter that was between those two points?

• 15:32Neil deGrasse Tyson?

  Fold two points in spacetime? Oh, so, ooh, so, well, you can't, because the two points in time will not correspond. They're two different places on the time axis. So you can't have time t equals zero in the same place as time t equals five, because they're different places on the axis. If you folded them, you're folding them in a higher dimension, and so they're kind of near each other. If you stepped above them in a higher dimension...

• 15:59Speaker 01

  But they're not actually the same.

• 16:01Neil deGrasse Tyson?

  They're not actually in the same place. And so, just to make that clearer, if you took a sheet of paper, and I've got one right here, even though it's radio, you can, you can listen to it. And I've got a sheet of paper, eight and a half by 11, and I'm curling the two edges, and I have the two edges sort of touching each other now.

• 16:18Speaker 01

  Yeah.

• 16:19Neil deGrasse Tyson?

  And I can say they're in the same place, but no, they're not.

• 16:20Speaker 01

  They're not actually.

• 16:21Neil deGrasse Tyson?

  They're not actually. Now, what I'll do is, I'll punch a hole through one to get to the other, a little wormhole, and I just warped the fabric of space, traveled through a wormhole, landed on the other side. Now I unfold a sheet of paper, and I just crossed the sheet of paper instantly in what might have otherwise taken me some, some unacceptably long period of time, such as what they do in Star Trek. They invoke their warp drives, they take their destination, warp their location close to it, they travel through this warp in the fabric of space and time, they unfold it, and they cross the galaxy during the TV commercial. That's how that works.

• 16:57Speaker 01

  That sounds awesome. That's a great commute.

• 16:58Neil deGrasse Tyson?

  And what would have otherwise taken a course the galaxy hundreds of thousands of years, even at the speed of light. So it's a legitimate way to cheat the laws of relativity.

• 17:07Speaker 01

  So the D train going uptown is like the exact opposite of that.

• 17:10Neil deGrasse Tyson?

  (laughing)

• 17:11Speaker 01

  It somehow manages to

• 17:12Neil deGrasse Tyson?

  To lengthen the time it takes you.

• 17:15Speaker 01

  (laughing) Wow, that's awesome.

• 17:18Neil deGrasse Tyson?

  That's a New York City reference there.

• 17:20Speaker 01

  That's a new, yes, that's a train that runs uptown in New York City. All right, next question here is from a website. It's from Drew McDowell. "I've heard Star Trek: The Voyage Home" used as a reference on the show before and actually had a burning question in my mind. They're talking about using certain velocities to use the sun's pull to time travel with. My question is, would there really be enough safe distance where the sun's pull could be used to gather enough speed, or would it just pull you in?"

• 17:45Neil deGrasse Tyson?

  So they're talking about Star Trek, uh, movie four.

• 17:49Speaker 01

  So it's like using what the gravity of your location with the sun to increase the velocity?

• 17:55Neil deGrasse Tyson?

  So Colin, what we'll do is we'll get back to that after this break.

• 17:58Speaker 01

  Oh, it's a cliffhanger. It's a cliffhanger.

• 18:00Neil deGrasse Tyson?

  We'll see you in a moment.

• 18:20Neil deGrasse Tyson?

  This is StarTalk Radio. I'm your host, Neil deGrasse Tyson, astrophysicist. We're in the Cosmic Queries, part of the Time Travel Show. And I found him wandering the streets, Colin Jost. Colin, welcome to StarTalk.

• 18:32Speaker 01

  Thank you. Great to be here.

• 18:33Neil deGrasse Tyson?

  He's gonna be reading questions submitted by all means of communication back to StarTalk. And by the way, Colin, if you want to find you, you're the Colin Jost.

• 18:43Speaker 01

  That's right.

• 18:44Neil deGrasse Tyson?

  On Twitter.

• 18:45Speaker 01

  Yeah.

• 18:46Neil deGrasse Tyson?

  So it's like

• 18:47Speaker 01

  And I've been enjoying all your tweets, too.

• 18:48Neil deGrasse Tyson?

  Oh, thank you.

• 18:49Speaker 01

  All the curiosity. So it's really cool.

• 18:50Neil deGrasse Tyson?

  Thank you. Thank you.

• 18:51Speaker 01

  A lot of great Mars facts that I did not know.

• 18:54Neil deGrasse Tyson?

  So before the break, you left off with a question. Who's it from?

• 18:58Speaker 01

  Uh, this is a question from Drew McDowell.

• 19:00Neil deGrasse Tyson?

  Drew McDowell. So he'd asked about the Star Trek, The Voyage Home, Star Trek IV, which has been dubbed Save the Whales. Right, that's the subtitle of that show.

• 19:10Speaker 01

  That's right.

• 19:10Neil deGrasse Tyson?

  Where they go back in time to the present day of the time of the film. So it was 1984, I think it was, or 85. And so he wants to know, is there an actual speed with which you can swing by slingshot past the sun, such as what they did in that show?

• 19:25Speaker 01

  Right.

• 19:25Neil deGrasse Tyson?

  In that movie, in order to go back in time?

• 19:27Speaker 01

  Right. And it says, can you use the sun's pull, but is there a safe enough distance that it wouldn't just pull you in?

• 19:34Neil deGrasse Tyson?

  Yeah. So first of all, you cannot do what they did in the show, in the movie.

• 19:37Speaker 01

  Regardless of.

• 19:38Neil deGrasse Tyson?

  Regardless, right. So, so just would nip that one in the bud.

• 19:41Speaker 01

  Yes.

• 19:42Neil deGrasse Tyson?

  Okay, so, and the only way you could do something like that is if you had vastly more powerful gravity than the sun. And you needed a, the fabric of space and time has to be so warped that, in fact, there's a colleague of mine who studies this, his name is Rich Gott. In fact, he's been on StarTalk before. He wrote a book called Time Travel in Einstein's Universe. And he found a solution to Einstein's equations that allows backwards time travel with a kind of a slingshot trajectory, but not around the sun. The sun does not disturb the fabric of space and time nearly enough.

• 20:19Speaker 01

  What would, what's the kind of thing that would?

• 20:21Neil deGrasse Tyson?

  Two black holes that are in orbit around each other. And so you'd have to do a kind of a a wiggly path around these black holes and you can end up in the past of your own world line before you had left to go on that trip.

• 20:35Speaker 01

  Wow.

• 20:36Neil deGrasse Tyson?

  Yeah, it's, it's a very whoa moment. And so Star Trek, it was more exciting to do it around the edge of the sun. Because visually, rather than just two black things in space, which is already black. But in principle, that, but in fact, I don't know that this equation had been discovered at the time the movie was conceived. They surely would have tapped it. They've got very good writers for Star Trek. So, so, yeah. And now, in terms of how close you can get to the sun, the, the ship, unless it had deflector shields working against thermal energy, uh, the ship would have just vaporized. Yeah.

• 21:07Speaker 01

  Yeah. And when, so like when you, that, that, uh, process he was talking about with the black holes, they have way more gravity, obviously.

• 21:14Neil deGrasse Tyson?

  Yes, with much more.

• 21:15Speaker 01

  What determines, what determines the gravity of an object or a, like, how do you get more gravity?

• 21:20Neil deGrasse Tyson?

  Yeah, yeah. You want more gravity? You don't weigh enough on Earth?

• 21:23Speaker 01

  I know, I know, opposite diet. What do we do?

• 21:26Neil deGrasse Tyson?

  So, yeah, two ways to gain weight. One of them is to eat more. Another one is to add more mass to the Earth, but keep it same size. So here's what happens. If Earth just got bigger, here's the problem. What makes you weigh more is how close you are to the center of gravity, the center of mass of an object. The closer you are to it, the more you will weigh. The farther away you are from it, the less you will weigh. All right? Another thing that matters is what is the mass of the object you're attracted to? So, you combine these together in an equation that Isaac Newton came up with, and you have two, two factors operating opposite each other. Okay? So, so, so, watch what happens.

• 22:07Neil deGrasse Tyson?

  The, um, if I take Earth and just make it bigger without increasing its mass?

• 22:14Speaker 01

  Your gravity's actually less.

• 22:15Neil deGrasse Tyson?

  That gravity's gonna be less. Gravity's gonna be less.

• 22:18Speaker 01

  And so, on the moon, our gravity is, there's less gravity. Is that because the mass is smaller?

• 22:22Neil deGrasse Tyson?

  Well, so, the moon is 1/81st as massive as the Earth.

• 22:27Speaker 01

  Gotcha.

• 22:28Neil deGrasse Tyson?

  1/81st as massive. So you'd think, well, you'd only weigh 1/81st of what you do now. If you were 160 pounds, you'd think you might weigh two pounds on the moon. No, you weigh 1/6th of what you do here. You weigh much more than you would otherwise weigh on the moon.

• 22:42Speaker 01

  Because you're closer to the center.

• 22:43Neil deGrasse Tyson?

  Because you're closer to the center of the moon. Exactly.

• 22:46Speaker 01

  Nice.

• 22:47Neil deGrasse Tyson?

  Exactly. So the moon has 1/6th Earth's gravity, even though it is 1/81st the mass of the Earth.

• 22:54Speaker 01

  There you go.

• 22:55Neil deGrasse Tyson?

  That, that, that's how it is.

• 22:56Speaker 01

  Problem solved.

• 22:57Neil deGrasse Tyson?

  And so, in fact, when people undergo weight loss programs, by the way, you could go to a mountaintop, and you're farther away from Earth, that's one way to lose-

• 23:04Speaker 01

  That's the easiest way to lose-

• 23:05Neil deGrasse Tyson?

  That's one way to lose weight, but you really-

• 23:07Speaker 01

  Plus, getting up there, you might lose some pounds.

• 23:09Neil deGrasse Tyson?

  Yeah, so, what really, people usually mean is that it's a mass loss problem. They want to lose mass.

• 23:14Speaker 01

  Yes.

• 23:15Neil deGrasse Tyson?

  Not just weight. Plus, you can go into orbit and weigh nothing.

• 23:17Speaker 01

  Right.

• 23:18Neil deGrasse Tyson?

  But you'll still be chubby if you went up, started that way.

• 23:21Speaker 01

  It's more expensive.

• 23:22Neil deGrasse Tyson?

  That's way more expensive than Jenny Craig.

• 23:25Speaker 01

  Yeah, that's a Richard Branson diet. All right, and then so this next question here is from Peter Baxter. It's from Google Plus and it says, if you took one year to get to the largest black hole in the universe, then you orbited it for one year, measured by a clock onboard the spaceship, at the closest safe orbit you could, which is kind of what we're talking about almost, then afterward, it took you one year to get back to Earth. How much time would have elapsed on Earth during the three years the astronaut experienced? Overall, is the astronaut traveling backward in time from the perspective of Earth?

• 24:00Neil deGrasse Tyson?

  Okay.

• 24:00Speaker 01

  It's like an intergalactic trains traveling.

• 24:03Neil deGrasse Tyson?

  There you go. Yeah, the train going from Chicago. Yeah, the word problem from hell, seventh grade. I'll start the answer to that, but we'll have to get back to the final part of that answer after this break. But let me begin by saying that it depends on how fast he traveled en route to the black hole and how fast he traveled en route back. And so we'll address that in just a moment when we come back to StarTalk Radio. By the way, you can find us on the web, starTalkRadio.net. See you after the break.

• 24:52Neil deGrasse Tyson?

  This is StarTalk Radio, where we bring the universe down to Earth. I'm Neil deGrasse Tyson here with Colin Jost. Colin, welcome to StarTalk.

• 25:01Speaker 01

  Thank you.

• 25:02Neil deGrasse Tyson?

  We're in the Cosmic Queries Time Travel Show and you're bringing questions called from the cosmos.

• 25:08Speaker 01

  That's right.

• 25:08Neil deGrasse Tyson?

  Right here into the studio.

• 25:10Speaker 01

  Mostly from Earth so far, but we'll see.

• 25:12Neil deGrasse Tyson?

  So far.

• 25:13Speaker 01

  Yeah.

• 25:13Neil deGrasse Tyson?

  And so we left off with someone who wanted some numerical.

• 25:17Speaker 01

  Yeah.

• 25:17Neil deGrasse Tyson?

  Tell me that again.

• 25:18Speaker 01

  They wanted you to fully solve a math problem. It was basically a year to get to a giant black hole. You spend a year orbiting it and then a year back to Earth. So three years total. Are you actually traveling backward in time? How much time has really elapsed for the traveler?

• 25:33Neil deGrasse Tyson?

  Okay, so.

• 25:34Speaker 01

  Or I'm sorry, how much time has elapsed on Earth?

• 25:36Neil deGrasse Tyson?

  Fortunately, we just came out of a break.

• 25:42Speaker 01

  Fully solved this whole thing and it was great to watch.

• 25:44Neil deGrasse Tyson?

  Dust off my.

• 25:47Neil deGrasse Tyson?

  My relativity equations and my, so here's the thing, the, a nearby black hole is, is in the constellation Cygnus, and it was the very first black hole ever discovered and confirmed. It's called Cygnus X1, and it's called X because it comes from an X-ray catalog of objects, and we came to learn that when a star is getting flayed by a black hole, a star that's in orbit around a black hole, that the descending material can, in its attempt to spiral down the toilet bowl, can be heated to very extreme, to extreme temperatures, so hot, that it not only radiates red hot, and white hot, and blue hot, blue hot is

• 26:29Neil deGrasse Tyson?

  the hottest among the temperature, among the colors that you can radiate, it actually radiates in X-rays. You can do the calculation and show that that's how hot the material is, and so the first X-ray telescopes in the 1960s and early 70s were essentially discovering black holes in our midst.

• 26:47Speaker 01

  They picked up something and they discovered it was that mass accelerating so fast?

• 26:51Neil deGrasse Tyson?

  An ordinary star doesn't give us X-rays of that level, and then you look carefully and the star's orbiting something, you can't even see what's there, there's your black hole.

• 26:58Speaker 01

  Wow, and is that, is it speed that's making it build and heat?

• 27:01Neil deGrasse Tyson?

  Exactly, so as the material spirals down, it speeds faster and faster and faster, and there's friction as it spirals down, friction with itself, as it tries to get into this tiny little hole, and that heats it up, it heats it up ferociously, and you get lots of ultraviolet light, lots of X-rays, and occasionally gamma rays.

• 27:20Speaker 01

  If they could sell tickets to watch that?

• 27:24Neil deGrasse Tyson?

  I would so do it.

• 27:25Speaker 01

  Yeah, that would be like an even better Cirque du Soleil.

• 27:27Neil deGrasse Tyson?

  To watch a star get flayed by a black hole, that's...

• 27:30Speaker 01

  That'd be great.

• 27:33Neil deGrasse Tyson?

  So, Cygnus X1 is 6,000 light years away, alright, so a beam of light, if you watched it, you'd have to wait 6,000 years for it to get there. So, you want to get there in one year?

• 27:44Speaker 01

  Uh, yeah.

• 27:45Neil deGrasse Tyson?

  Okay.

• 27:45Speaker 01

  I would love to.

• 27:46Neil deGrasse Tyson?

  You want to get there in one year. Okay. So by your, by your own time. So we get bringing the equations of relativity.

• 27:53Speaker 01

  Mm hmm.

• 27:54Neil deGrasse Tyson?

  Um, if you must know, um, you're comparing two times the time you on earth would measure versus the time the person traveling.

• 28:01Speaker 01

  Experiences.

• 28:02Neil deGrasse Tyson?

  Would, would experience. And in there, there is a factor of the square root of one minus the V squared over C squared. And V squared is your velocity. C squared is of course the speed of light.

• 28:12Speaker 01

  Yes.

• 28:12Neil deGrasse Tyson?

  There it is. It's just.

• 28:13Speaker 01

  Of course.

• 28:14Neil deGrasse Tyson?

  Did I have to say?

• 28:15Speaker 01

  What else? No.

• 28:15Neil deGrasse Tyson?

  Of course.

• 28:16Speaker 01

  I wasn't, I wasn't thinking cookie. I was thinking.

• 28:20Neil deGrasse Tyson?

  All right. So what happens is the faster you go, the slower time ticks for you. And so we're going to slow down your time so much so that only one year passes by. Meanwhile, 6,000 years passes by for people on earth. That speed is 99.9999986% of the speed of light.

• 28:44Speaker 01

  I was going to guess that.

• 28:46Neil deGrasse Tyson?

  So that's damn near the speed of light. The point is you're going to speed essentially the speed of light, but not quite, but close enough so that we watching you, it'll take you 6,000 years to get there. You, however, your clock, your watch, your metabolism, your brain thoughts, the timer on your microwave oven, everything in your ship has slowed down as far as we can tell, looking at you. Okay? So there it is.

• 29:14Speaker 01

  You're experiencing, you think it's a year, but we would say it's 6,000 years from here.

• 29:19Neil deGrasse Tyson?

  That's correct. You're, I think you're taking 6,000 years and you're just moving really slow.

• 29:24Speaker 01

  Wow.

• 29:25Neil deGrasse Tyson?

  That's right. So that's 6,000 years there.

• 29:26Speaker 01

  So, so if I'm someone who's perennially late and I'm trying to find up kind of find new excuses for my employer, this might be one I might want to look into.

• 29:36Neil deGrasse Tyson?

  Maybe we'll find you a black hole to do this. So it's 6,000 years there. Then we just add the year that you're in orbit around the black hole. 6,000 years back, you would have gone into our future by 12,001 years and you would have aged only three years. There it is. But everyone would have forgotten about you.

• 29:53Speaker 01

  So people wouldn't even be able to say, "Oh, you look so good," because they'd be like...

• 29:57Neil deGrasse Tyson?

  Anyone who would've said that would've been long decomposed in the earth. When we come back, our final segment here in Cosmic Queries, we'll see you in a moment.

• 30:27Neil deGrasse Tyson?

  We're back in the Cosmic Queries portion of StarTalk Radio. By the way, we're in the Twitterverse at StarTalk Radio. Like us on Facebook. Guess what we're called? We're called StarTalk Radio. And of course, you can get our archive of shows and read blogs and get engaged in our website, StarTalkRadio.net. And as always, I've got a comedian with me here in the studio who's reading me the questions. Colin Jost, who's a lifetime comedian, ever since you were a kid in elementary school.

• 31:01Speaker 01

  Long as I can remember, I think.

• 31:03Neil deGrasse Tyson?

  Were teachers complaining about you, or are they...?

• 31:06Speaker 01

  Yeah, they were surprisingly supportive, I would say.

• 31:10Neil deGrasse Tyson?

  Really?

• 31:10Speaker 01

  When I look back, I'm like, "Why were they letting me do this?"

• 31:12Neil deGrasse Tyson?

  Okay, so that meant you were not a disruptive comedian. You were just...

• 31:15Speaker 01

  No, I somehow managed to, I guess, convince them that it was...

• 31:19Neil deGrasse Tyson?

  That was a good thing. It's for your own good that I'm telling these jokes. Excellent, excellent. So, we're doing Cosmic Queries. This is our time travel show, and people wrote in. So what do you have?

• 31:31Speaker 01

  Here's one that I think's really interesting.

• 31:33Neil deGrasse Tyson?

  Oh wait, by the way, we left off with this guy asking, he wants to go to the nearest black hole, take a year, hang out for a year and come back. And I said, "You know, he ages three years, and we age 12,001." I was just trying to back, reverse that and say, "Suppose Cro-Magnon Man, 12,000 years ago, figured this out, and they just showed up today."

• 31:53Speaker 01

  That might explain Geico. You've created a scientific explanation for the Geico commercial.

• 32:02Neil deGrasse Tyson?

  I was wondering how we would finally resolve.

• 32:05Speaker 01

  How we would get to it.

• 32:05Neil deGrasse Tyson?

  They had already figured out time travel back then and they just showed up. So what else you got?

• 32:11Speaker 01

  This is a question from Facebook, from Daniel Owens. And he writes, what would be the most surprising thing to not find if you travel 100 years into the future? As in, they haven't figured out that yet? So this is more speculative, I think, question on your part, you know, for you to answer.

• 32:28Neil deGrasse Tyson?

  I'm surprised at stuff we haven't figured out today. I don't have to go, you don't need to send me 100 years into the future. You know, if an alien visited us today, I'd be embarrassed. You know, look, we're still pulling energy out of the ground and we still fight each other. We fight wars over this, like, oil. We'd be the laughing stock of intelligent species in the galaxies. And they said, what do you do with volcanoes? We run. What do you do with hurricanes? We run. What do you do with tornadoes? We run. Haven't you solved any? No, I'm embarrassed.

• 33:01Speaker 01

  Yeah.

• 33:01Neil deGrasse Tyson?

  This is the 21st century. We should be in charge of the Earth and not have the Earth be in charge of us.

• 33:07Speaker 01

  Imagine if they came and the aliens came back and they just found like a Spencer's Gifts and they thought that was like, that was like their leading thing instead of a museum, it would be even worse.

• 33:15Neil deGrasse Tyson?

  Yeah, you know, you don't know who they meet first, right? They land in some nudist colony or something or whatever, you know. I always wonder if they had ever, maybe they've already landed like in Times Square, but nobody noticed because they just fit right in.

• 33:29Speaker 01

  There's just so much going on there already. Like, uh huh, yeah, where do you want to go?

• 33:34Neil deGrasse Tyson?

  Exactly. They land in Hollywood, they just fit in, you know? No, if they landed, I tweeted this, there was some very attractive alien in full garb.

• 33:43Speaker 01

  Oh, yeah.

• 33:44Neil deGrasse Tyson?

  But I just tweeted, I said, I meant the only, only real alien, but no one noticed. They accidentally landed in Comic Con.

• 33:50Speaker 01

  I know, that would be the worst place for an alien to land, that's true.

• 33:53Neil deGrasse Tyson?

  Total worst place, total worst place.

• 33:54Speaker 01

  That should be probably the, at least the beginning of a movie of an alien coming Earth.

• 33:58Neil deGrasse Tyson?

  Exactly, exactly.

• 33:59Speaker 01

  It's a really good opening scene.

• 34:00Neil deGrasse Tyson?

  So this question was what?

• 34:01Speaker 01

  It was kind of, what do you think in the, in 100 years from now, you're going to be like, you're going to be shocked that I haven't?

• 34:06Neil deGrasse Tyson?

  Okay, if we still are not in control of Earth forces that would otherwise kill us. I'd be very disappointed.

• 34:12Speaker 01

  Right.

• 34:13Neil deGrasse Tyson?

  One day I want to tap a volcano for its energy.

• 34:15Speaker 01

  Of course.

• 34:16Neil deGrasse Tyson?

  And then.

• 34:16Speaker 01

  And some places I do, you know, I mean, I remember going to Iceland and seeing some of the. Have they have there.

• 34:22Neil deGrasse Tyson?

  The geothermal energy. Yeah, yeah. Yeah. I mean, it's maybe we have to put beer in the volcano and then we'll learn how to tap. Tap kegs just fine. So to somehow tap the cyclonic energy of hurricanes.

• 34:34Speaker 01

  Yeah.

• 34:35Neil deGrasse Tyson?

  I'd be surprised if we haven't sort of figured that one out.

• 34:37Speaker 01

  Have you seen how they have, you know, people have proposed things out in the ocean that are floating, that are circulating the water temperature? So it never gets that hot and cold or.

• 34:47Neil deGrasse Tyson?

  Oh, okay. So what they're trying to do is prevent the hurricane happening in the first place. Well, I don't mind a hurricane if it's a source of energy for us to tap.

• 34:53Speaker 01

  Of course, yeah.

• 34:54Neil deGrasse Tyson?

  So the hurricane is ready to strike the coast, then you put some device in the middle, sucks all the energy.

• 34:59Speaker 01

  Yeah.

• 34:59Neil deGrasse Tyson?

  And then you power the city that the hurricane would have otherwise leveled.

• 35:02Speaker 01

  That's a pretty good come up for the hurricane.

• 35:04Neil deGrasse Tyson?

  Exactly. But in fact, what's really going on there is that you're tapping solar power. The sun is what's driving the hurricane. So in fact, there's a lot of wasted solar energy first that's just hitting rooftops that don't have solar panels. But also solar energy that is otherwise creating things that would destroy us. And also just earthquakes, the amount of energy in an earthquake. So I want to be in command of Earth's forces a hundred years from now. And I'd be disappointed if we weren't.

• 35:30Speaker 01

  Yeah, that's a really good, uh, goal.

• 35:33Neil deGrasse Tyson?

  We're running out of time. Oh, my gosh.

• 35:35Speaker 01

  My last thing, I was curious because it's all over the place now is with the Higgs boson particle. How does that affect time travel? Are there any thoughts about how that can either explain or help?

• 35:45Neil deGrasse Tyson?

  Yeah, it's not obvious that it could affect time travel, but if you get really science, if I can get really science fiction on you.

• 35:51Speaker 01

  Yeah, please.

• 35:51Neil deGrasse Tyson?

  Right. Uh, the Higgs boson controls the mass of particles. Imagine you go into a Higgs boson spa. It changes your mass just by walking in and walking back out.

• 36:01Speaker 01

  Wow.

• 36:02Neil deGrasse Tyson?

  That would be total command of particle physics. That would be an awesome weight loss program.

• 36:06Speaker 01

  Yeah, I'm sure that would be the first thing someone uses it for is to commercialize. Want to look 10 pounds thinner?

• 36:13Neil deGrasse Tyson?

  Not to advance our understanding of the universe, but to take fat off your belly and butt. Anyhow, we got to call it a day. Thanks, Colin, for being on StarTalk Radio.

• 36:23Speaker 01

  It's a pleasure. Thank you for having me.

• 36:24Neil deGrasse Tyson?

  You've been listening to StarTalk Radio. I'm Neil deGrasse Tyson, signing off, as always, bidding you to keep looking up.