Traveling Through Space and Time, with Janna Levin

What awaits us beyond our solar system? Janna Levin and comedian Matt Kirshen answer questions on interstellar travel, black holes, and the furthest reaches of our universe. What mysteries can we uncover once we venture further beyond our home star?

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.

• 0:14Janna Levin?

  Welcome to StarTalk All-Stars. Hi, Matt.

• 0:18Matt Kirshen?

  Hey, Jana.

• 0:19Janna Levin?

  I am your All-Stars host, Janna Levin. I am a professor of physics and astronomy at Barnard College of Columbia University and also Director of Sciences here at Pioneer Works where we are. And I'm welcoming Matt, who is co-host of Probably Science, as well as a hysterical comedian.

• 0:36Matt Kirshen?

  Thank you.

• 0:37Janna Levin?

  But his role here is just to, like, beam a pail today.

• 0:40Matt Kirshen?

  I want to know how you end up on the All-Stars. Like, how does this work?

• 0:43Janna Levin?

  Yeah, I don't know how you do end up on the All-Stars. Who selected you?

• 0:46Matt Kirshen?

  I don't know. I think I just got selected. I think you got called up to the main team, and then I'm just subbing in.

• 0:51Janna Levin?

  I think I selected you.

• 0:52Matt Kirshen?

  Well, I appreciate that.

• 0:54Janna Levin?

  Well, welcome. Today, we're going to do Cosmic Queries. It's been a long day, and we're, like, you've been traveling the world.

• 1:00Matt Kirshen?

  I have. By the world, you mean the west to the east coast of America.

• 1:03Janna Levin?

  Isn't that the world?

• 1:05Matt Kirshen?

  It is, as far as baseball is concerned. It's the World Series area.

• 1:11Janna Levin?

  And if only we could, you know, control time, then it would all be so much more relaxing to have this conversation.

• 1:19Matt Kirshen?

  Well, there may or may not be questions about that right now.

• 1:21Janna Levin?

  Oh, my gosh, really?

• 1:23Matt Kirshen?

  I don't know.

• 1:24Janna Levin?

  I had no idea.

• 1:27Matt Kirshen?

  Well, these questions, these are all themed. The hashtag was #CQInterstellarTravel. I think the CQ is Cosmic Queries, so it's just the interstellar travel bit.

• 1:39Janna Levin?

  I should have known that lingo.

• 1:41Matt Kirshen?

  Right.

• 1:41Janna Levin?

  I feel a little slow. Okay.

• 1:43Matt Kirshen?

  So, everything here is interstellar travel-based. Manos on Twitter says, "Unless we come up with a way to rip spacetime, wormholes, etc., it's not going to happen. Am I right? Is Manos right?"

• 1:57Janna Levin?

  About temporal travel. Well, I mean...

• 2:00Matt Kirshen?

  About space travel, I think, specifically.

• 2:02Janna Levin?

  Okay, well, so here's the thing about... Well, let's do time travel first. So, here's the thing about time travel, is that the question... There's two points to that question. One is whether we're going to do it. Right, through technology, or whether it's possible in terms of nature. So it's possible, nature could create its own time machine. And that we don't have to do it technologically, but it wouldn't be us, right? Some, some other entity in the universe. Like you could have two cosmic strings crossing that create these weird conical folds that allow some, like some critter, not where we live, right? But some critter to do a loop where they come back in time. So that's actually naturally possible, doesn't require technology.

• 2:46Matt Kirshen?

  So that doesn't contravene the rules of physics, the laws of physics as we know them?

• 2:50Janna Levin?

  You know, it's really disturbing, but the laws of physics as, as Einstein set them down, allow for time travel. And, and there's a couple of circumstances that occur naturally, but not in our universe. So Gödel, the famous mathematician, knew that there was a rotating spacetime. Like if the entire universe was spinning, which is not our universe, right? So it's not gonna be us. But if the entire universe was spinning, that he could find a path, a world line, a, a, the line of some naturally occurring entity that would go into its past. And he used to walk to the institute in Princeton with Einstein and talk about it. And Einstein was astounded that Gödel found the solution, but didn't disbelieve it,

• 3:33Janna Levin?

  understood that it was, it was allowed, and his theory was very concerned.

• 3:37Matt Kirshen?

  But then didn't Gödel also starve to death because his wife went to hospital?

• 3:41Janna Levin?

  Um, yeah.

• 3:43Matt Kirshen?

  So, you know.

• 3:45Janna Levin?

  So that happened, but.

• 3:47Matt Kirshen?

  So on the one hand, he knew a lot more about space and time than I do. But on the other hand, I can cook.

• 3:53Janna Levin?

  Yeah, you can, yeah, you can feed yourself.

• 3:55Matt Kirshen?

  So I'd say we're pretty much equal.

• 3:57Janna Levin?

  Yeah, you know, it's, um, you know, nature gives greatness and weakness in equal measure.

• 4:03Matt Kirshen?

  And that's a law?

• 4:04Janna Levin?

  We're all about average. We're all about average at the end of the day.

• 4:06Matt Kirshen?

  So interstellar travel, is that gonna be possible without something like wormholes?

• 4:11Janna Levin?

  Um, so, man, if we could figure out what the dark energy was, and we could make it, then you might be able to do warp drive, which would allow interstellar travel. So right now, Voyager spacecraft has just broken out of the sun's magnetic influence, right? It's barely, barely out of the solar system. It's the first interstellar probe humans have ever sent, right? And we, we mailed it in like the seventies. So it's taken its time. To get out there, and it'll take something like 10,000 years for Voyager to hit another star system, or something like that. But if you were traveling at the speed of light, you could get there in a few years. So if we can harness things like dark energy, if we figure out what it is, and we can make

• 4:56Janna Levin?

  it at the Large Hadron Collider, and we can like, put it in a barrel, and take it out into space, we could suck distant parts of space closer, step across it, and then expand it again. And so it wouldn't be that we'd be traveling faster than the speed of light, it's that we'd be pulling spacetime in, making a small step for humankind, and then pushing it back out again. And you can do that faster than the speed of light and not violate any laws. So that's kind of what warp drive would look like. Not technologically impossible. It's just very unlikely, given the way, you know, the vote goes in Congress this week. You know what I'm saying?

• 5:35Matt Kirshen?

  Right.

• 5:35Janna Levin?

  Like, the way North Korea's looking.

• 5:37Matt Kirshen?

  So we're likely to blow ourselves up before...

• 5:39Janna Levin?

  Yeah.

• 5:40Matt Kirshen?

  I gotcha.

• 5:40Janna Levin?

  Yeah.

• 5:41Matt Kirshen?

  Well, that's a dark way to end it.

• 5:43Janna Levin?

  Odds are good, yeah.

• 5:44Matt Kirshen?

  So Neil Cochran on Twitter asks, "If we can achieve the speed to explore the universe, isn't inertial dampening going to be an issue?"

• 5:53Janna Levin?

  Inertial dampening, um...

• 5:56Matt Kirshen?

  What is inertial dampening first?

• 5:58Janna Levin?

  Inertial dampening really only matters, well, I guess it matters anywhere, because there's gravity anywhere. Um, so, it's hard to push a car.

• 6:08Matt Kirshen?

  Uh-huh.

• 6:09Janna Levin?

  Um, but it's easier to push me around.

• 6:12Matt Kirshen?

  Right.

• 6:13Janna Levin?

  Right. And that's because I have less inertia than the car. But in completely, um, outer space, it's not that expensive to push anything.

• 6:22Matt Kirshen?

  Right.

• 6:23Janna Levin?

  It's really easy. Um, it's really quite easy. But F equals ma, you know, Newton's laws. Oh my god, a sudden equation in audio, but everyone knows F equals ma, and if they don't, they're gonna learn it today. Newton's laws, the force equals the mass times the acceleration. Yes, it requires greater force, the greater something, the greater the inertial mass. That's true, but it's still pretty easy to push a car in outer space. It's a lot easier than it is to, to do it down here on Earth.

• 6:49Matt Kirshen?

  So you just, surely, whenever you're moving anything across space, you just need as much deceleration as you have acceleration?

• 6:57Janna Levin?

  Yeah, I mean-

• 6:58Matt Kirshen?

  On the other end.

• 6:58Janna Levin?

  The thing, the difference is, is that if I push something in space, okay, maybe it's a little bit expensive to get it going.

• 7:04Matt Kirshen?

  Yep.

• 7:05Janna Levin?

  But once it's going, like, I can pretty much just kick back and it's gonna go forever.

• 7:09Matt Kirshen?

  Mm-hmm.

• 7:09Janna Levin?

  Right? It's gonna be very little that slows it down or stops it, unlike on Earth, where there's all kinds of forces, friction and gravity, that slows things down. And, you know, if I get something launched in interstellar space, it'll keep going for a long, long time. I see you reading.

• 7:25Matt Kirshen?

  I am reading.

• 7:26Janna Levin?

  I see you looking pensive. What do you got?

• 7:27Matt Kirshen?

  I am reading. So, um, so Marco Pedrosso-

• 7:32Janna Levin?

  Do I get to ask you some of these questions?

• 7:33Matt Kirshen?

  Yes, throw these questions at me, professor of fast throw physics. And see how the idiot comedian fares.

• 7:42Janna Levin?

  Come on, you have a degree in math.

• 7:44Matt Kirshen?

  I, I do, but I, I scraped my way through it. And that was well over a decade ago, and I have done nothing with it since, apart from create a podcast that tenuously has science in the title. So-

• 7:56Janna Levin?

  It's only probably science.

• 7:57Matt Kirshen?

  That's why we put it in there.

• 7:58Janna Levin?

  It's not definitively science.

• 7:59Matt Kirshen?

  It's the, it was named very carefully. The only thing we do carefully on that show.

• 8:05Janna Levin?

  Hey, I've been on that show.

• 8:07Matt Kirshen?

  You have. We carefully book people who know a lot more than we do. That's the other thing we do carefully. Marco Pedrosso on Twitter says, "Guys, honest question." I like that little preface.

• 8:19Janna Levin?

  As opposed to the rest, aren't? Like, is he implicating the others?

• 8:22Matt Kirshen?

  Yeah, or implicating the-

• 8:23Janna Levin?

  His other friends, who like 30 seconds earlier pressed send?

• 8:26Matt Kirshen?

  Every other question you're getting is bullshit, but this one-

• 8:29Janna Levin?

  This one's honest.

• 8:33Janna Levin?

  Well, my answer may or may not be, depending.

• 8:35Matt Kirshen?

  Yeah, so, um, "Honest question. Ships navigating deep space should be shrouded in total darkness, right?"

• 8:46Janna Levin?

  Well, I mean, except for the light from the galaxy. That's not total darkness. What's deep space? Galactic space?

• 8:54Matt Kirshen?

  I don't know. What counts as deep space?

• 8:56Janna Levin?

  Okay, away from the sun, it gets dark. I mean, it's pretty dark at Pluto. It gets dark the further away you are from any individual stars. I mean, I guess you could go intergalactic, and that's pretty dark, yeah.

• 9:06Matt Kirshen?

  But then you would still have-

• 9:07Janna Levin?

  Wait, we're only on the first clause. He's got a comma here. There's more coming. Wait, he would have what?

• 9:11Matt Kirshen?

  No, that is the full question. So, yeah, so hang on, just thinking. I don't know what you count as deep space. Do you mean, is deep space the space between individual stars? Or is it the space between individual galaxies, or?

• 9:23Janna Levin?

  Can we write him back and ask him what he means?

• 9:24Matt Kirshen?

  I don't know. I mean, it's an honest but ambiguous question.

• 9:27Janna Levin?

  If it's interstellar, it's dim. If it's intergalactic, it's really pretty dark.

• 9:32Matt Kirshen?

  But you are still getting the light from millions of galaxies, but each of those is just a pinpoint, like a single star, right?

• 9:37Janna Levin?

  Yeah, like if you were a planet, a rogue planet, that had somehow been ejected from the galaxy, and you were floating-

• 9:44Matt Kirshen?

  Which I'm sure happens, right?

• 9:44Janna Levin?

  Okay, planets, it's hard to eject, but maybe stars, an entire system. So, like, let's say when we collide with Andromeda, where somehow the two galaxies, the Milky Way Galaxy and Andromeda Galaxy collide, and our solar system gets knocked about.

• 9:58Matt Kirshen?

  Right.

• 9:59Janna Levin?

  And it gets thrown, possibly unlikely, but possibly completely out of the galaxy. So, the whole solar system's floating, intergalactic.

• 10:07Matt Kirshen?

  And it takes us with it, because we're just still traveling in its wake and its gravitational?

• 10:11Janna Levin?

  Yeah, it's actually, it's probably kind of normal for us, because the sun's still illuminating us.

• 10:15Matt Kirshen?

  Right.

• 10:16Janna Levin?

  So, we have to lose the sun.

• 10:18Matt Kirshen?

  Okay.

• 10:18Janna Levin?

  Okay, so let's say we make up some scenario where some evil genius ejects the planet and sends it intergalactic. It's gonna be dark, yeah. If you could survive that utter darkness, you would see galaxies and you would see other things in the universe, but you would not have the warmth to survive, probably.

• 10:39Matt Kirshen?

  Right.

• 10:40Janna Levin?

  Yeah.

• 10:40Matt Kirshen?

  Or the light to see anything in your locality.

• 10:43Janna Levin?

  Right, exactly.

• 10:45Matt Kirshen?

  There wouldn't be enough light coming from these galaxies or stars to then bounce off things and illuminate.

• 10:49Janna Levin?

  Right, but imagine, like, the decrease in light pollution.

• 10:52Matt Kirshen?

  I was just thinking that. That would probably be a great way to go stargazing.

• 10:56Janna Levin?

  Great stargazing, seriously good astronomy.

• 10:58Matt Kirshen?

  Because right now, we're in New York City, which has to be one of the worst places in the world for light pollution, right?

• 11:03Janna Levin?

  It is terrible, but we are in Red Hook. And so we're in, as far as New York City goes, we're probably ideally located because we're right on the water.

• 11:10Matt Kirshen?

  Mm-hmm.

• 11:11Janna Levin?

  We're looking at Manhattan, which is way, way over there. And there's not a lot of street, there's not, not a lot of streetlights or a lot of light pollution around here. We actually have pretty good viewing.

• 11:20Matt Kirshen?

  That's pretty good. I like, I, I live in Los Angeles most of the year and that's terrible. But again, you can just go a little bit out of town. You can get into sort of Joshua Tree, that kind of area, and suddenly you're in the middle of a desert.

• 11:32Janna Levin?

  Yeah. Yeah. I mean, strictly speaking, Los Angeles is a desert.

• 11:36Matt Kirshen?

  It is.

• 11:36Janna Levin?

  I don't mean that as a jab, I just mean that literally, like technically it's a desert.

• 11:39Matt Kirshen?

  And you sometimes forget that.

• 11:41Janna Levin?

  Yeah.

• 11:42Matt Kirshen?

  Because you're surrounded by the trappings of non-desert, like a lot of grass that has been expensively imported.

• 11:49Janna Levin?

  Palm trees, which have been imported.

• 11:51Matt Kirshen?

  With a lot of unnecessary water usage and you forget that. And then you go out for the day.

• 11:56Janna Levin?

  And you're looking down so much that you forget to like, look up at the sky.

• 11:59Matt Kirshen?

  Yeah, and then you realize, why am I so exhausted today? Oh, because I haven't drunk water and I'm in a desert. Like, it's a little trip for anyone, little tip for anyone who's visiting California, drink water.

• 12:10Janna Levin?

  Any questions about hydration?

• 12:12Matt Kirshen?

  Yeah, throw them my way. Remember to tag them, CQ Matt's Hydration Tips.

• 12:20Matt Kirshen?

  Okay, so we're, we're on to our first Instagram question, Jana.

• 12:26Janna Levin?

  Does it come with a picture?

• 12:28Matt Kirshen?

  Uh, it doesn't. It doesn't, it's just, uh, it's just text. Rishi Rish, um, on Instagram asks, "Traveling at light speed is now just an engineering problem. Care to explain?"

• 12:42Janna Levin?

  Really?

• 12:43Matt Kirshen?

  Uh, so that, that's in quotes, the first bit of that's in quotes. So I'm wondering whether that's something that Neil or someone else on the show has said at some point.

• 12:51Matt Kirshen?

  Because it's, or, or this is just something that Rishi Rish has read. In quotes, it says, "Traveling at light speed is now just an engineering problem," close quotes.

• 13:01Janna Levin?

  I'm gonna actually back him up on this. So there are these nano satellites that are like the size of a postage, a postage stamp that they want to put like a couple of computer chips on and send into space.

• 13:13Matt Kirshen?

  Okay.

• 13:14Janna Levin?

  And, um, they're gonna kind of laser them, like...

• 13:19Janna Levin?

  Accelerate them with the pressure of a laser. And they think that they can get them to lights, very nearly light speed. Meaning, meaning a fraction, like even if it's point one, the speed of light, that's really fast.

• 13:35Matt Kirshen?

  Yep.

• 13:36Janna Levin?

  That's insanely fast. So light speed is 300,000 kilometers per second, so you're going 30,000 kilometers per second. That's insane.

• 13:42Matt Kirshen?

  Yeah.

• 13:43Janna Levin?

  And they think they can do it with these tiny postage stamp things because they're so light. So what happens when you try to boost things to the speed of light is that it becomes energetically more and more expensive. Technically, the inertial question, we can tie it to one of the earlier questions, things get effectively heavier. They get more inertia.

• 14:01Matt Kirshen?

  This is something, this is something I vaguely remember from, this is special relativity, right?

• 14:06Janna Levin?

  Yeah, special relativity, just straightforward, special relativity.

• 14:08Matt Kirshen?

  The faster something gets, the closer the speed of light, the heavier it becomes, the more inertia it gets.

• 14:11Janna Levin?

  Right, the more inertia it gets, and so the harder it is, like, you know, to push it. And so, so in that sense, it is just an engineering problem. So you want to send postage stamp sized stuff.

• 14:24Matt Kirshen?

  Right. Because also in space-

• 14:26Janna Levin?

  You can't send astronauts and fuel and rockets because that, that as an engineering problem is insurmountable at the moment.

• 14:33Matt Kirshen?

  But in space, you also have the advantage that you talked about at the beginning of the show where there is almost nothing slowing things down. So any acceleration is just cumulative. You can just keep accelerating things.

• 14:44Janna Levin?

  That's right. That's right. So you can get something to some speed, maybe it's a hundredth or a thousandth the speed of light, and it'll pretty much keep going that way. I mean, it's, you know, if it's really tiny especially, because it won't be slowed down by passing by big planets or passing by new star systems.

• 14:57Matt Kirshen?

  Or even particles just floating in space.

• 14:59Janna Levin?

  Well, that could be a problem.

• 15:00Matt Kirshen?

  Okay.

• 15:01Janna Levin?

  That could be a problem, like winds. Solar winds could blow you back pretty bad, you know. So that could be a concern for these projects, I think, in general. But they're talking about sending many, right? So just if they send many, it's like running a lot of horses.

• 15:16Matt Kirshen?

  So how-

• 15:17Janna Levin?

  And you just hope a couple make it.

• 15:18Matt Kirshen?

  So where is this laser that's going to be powering it going?

• 15:21Janna Levin?

  It's like turtles.

• 15:22Matt Kirshen?

  Yeah.

• 15:23Janna Levin?

  Yeah, so the, I mean, that sounds very sci-fi. I don't know that much about the technology, but I guess the laser's mounted here on Earth? And, you know, light doesn't tire. It can make it as far as you can send it. And they'll just keep blasting this thing. So they, I think they recently, wasn't there, um, from the ISS, I think one of the astronauts manually tossed out a nanosatellite, literally. Like he was spacewalking and he just sort of like

• 15:48Matt Kirshen?

  Sprinkled it.

• 15:49Janna Levin?

  Threw it.

• 15:50Matt Kirshen?

  Yeah.

• 15:50Janna Levin?

  And hoped for the best. Um, so I think they're starting like preliminary ideas on these tiny, tiny satellites. Yeah.

• 16:00Matt Kirshen?

  That's a, but you could never actually,

• 16:04Matt Kirshen?

  I said traveling at light speed. Now, at light speed itself, anything that has mass can never reach

• 16:10Janna Levin?

  No.

• 16:10Matt Kirshen?

  Light speed, right?

• 16:11Janna Levin?

  That's right. It can never reach light speed because it becomes infinitely heavy and infinitely hard to push just that little bit further, right? But it can go a fraction of the speed of light. It's pretty good. So, I mean, point one, the speed of light, like we said, that's 30,000 kilometers per second. I mean, how long did it take you to get from California? Half our ways, California.

• 16:31Matt Kirshen?

  We would definitely, so.

• 16:33Janna Levin?

  3,000 miles and it took you six hours?

• 16:37Matt Kirshen?

  I know.

• 16:37Janna Levin?

  Okay. So you would have gotten here in a fraction of a second.

• 16:39Matt Kirshen?

  And that, that's better. And I think we should really work towards that.

• 16:44Matt Kirshen?

  Cause you could even deal with economy class in that.

• 16:46Janna Levin?

  Are you for that?

• 16:47Matt Kirshen?

  I could do that. Yeah. Cause even like economy class in that kind of speed, you sort of be just cramped. Yeah.

• 16:51Janna Levin?

  Yeah. Two seconds. You know, the boredom of getting on the plane and.

• 16:55Matt Kirshen?

  Right. You'd have to add a couple of seconds on either end as well for the getting on, getting off. You're always stuck behind the one person who can't carry their bag.

• 17:11Speaker 03

  I'm Jasmine Wilson and I support StarTalk on Patreon. This is StarTalk with Neil deGrasse Tyson.

• 17:23Janna Levin?

  I'm ready to take more of these cosmic queries.

• 17:25Matt Kirshen?

  Well, let's go with-

• 17:26Janna Levin?

  Did people send us more?

• 17:28Matt Kirshen?

  They certainly did. We've got to hold back to that. I was, at the beginning, I was like, are we going to have enough questions? So I was kind of spacing it out. And now I'm like, are we going to get through them?

• 17:36Janna Levin?

  Oh, hurry up, hurry up.

• 17:36Matt Kirshen?

  Are we going to get through them? So BoCraft on Twitter says, "Assuming interstellar travel is mastered by humans, what about it excites you and what scares you?"

• 17:48Janna Levin?

  Interstellar travel. Well, I mean, what about it would not be exciting? You know, it's amazing. We would go to a- we have planets now. We have exoplanets by the thousands in our own galaxy.

• 18:00Matt Kirshen?

  That is something strange that's happened in the last-

• 18:03Janna Levin?

  Ten years.

• 18:04Matt Kirshen?

  That's really recent, right?

• 18:05Janna Levin?

  Really recent.

• 18:05Matt Kirshen?

  The size of exoplanets has gone from, "We might find one," to, "We can't stop finding these things."

• 18:10Janna Levin?

  So now, pretty much, they think that, I mean, minimum one-fifth of all star systems have planets. There's 100 billion stars in the galaxy, so one-fifth is a big number, right?

• 18:21Matt Kirshen?

  So that's, again, the chance of us finding something approximating, like, what we- life of some way.

• 18:26Janna Levin?

  Right. So each one of those systems could have multiple planets. So that makes more planets than there are stars.

• 18:32Matt Kirshen?

  And each of those planets could also have moons, because like-

• 18:34Janna Levin?

  Yeah, and the moons are also habitable. So probably, like, if you were in the solar system, we talk about Mars, but like, in an emergency, don't go to Mars. Go to, I don't know, Europa.

• 18:44Matt Kirshen?

  We just had something about Europa on our show, and that's the only reason I know this, but I happen to know that Europa has a lot of water and-

• 18:51Janna Levin?

  Yeah. Well, you know, I don't work on anything that happened more recently than a billion years ago, so-

• 18:55Matt Kirshen?

  Right.

• 18:55Janna Levin?

  Europa's like-

• 18:57Matt Kirshen?

  This is way into practicality. You're this stuff. You're for the audio only, the people I'm pointing to a whiteboard behind us, covered in symbols and squiggles.

• 19:06Janna Levin?

  Yeah, that's the good stuff.

• 19:07Matt Kirshen?

  Yeah.

• 19:08Janna Levin?

  But, so, interstellar travel would mean we could actually go visit these planets. But like Interstellar the Movie, which was quite accurate in a lot of ways, because Kip Thorne, who's the great astrophysicist from Caltech, wrote the treatment for that movie and was very involved in consulting on it. And a lot of that's incredibly accurate. You would burn a lot of years traveling. It might be that your years were shortened. Like, you could interstellar travel for like, five years and come back to the Earth, but 100 years might have passed on Earth. So, um, so that's a pretty big sacrifice.

• 19:41Matt Kirshen?

  That's a scary thing.

• 19:42Janna Levin?

  Like, the guys who go up to- so I met Scott Kelly today, the astronaut.

• 19:45Matt Kirshen?

  That's right.

• 19:46Janna Levin?

  It was really great hanging out with him, like, for the few minutes. I don't know if it was great for him. I wanted to ask him stuff and I couldn't think of anything, but he probably aged a few seconds more slowly than his twin brother because of being on the International Space Station.

• 20:01Matt Kirshen?

  That's right. Scott Kelly was famed, has a twin brother who was also an astronaut, right?

• 20:05Janna Levin?

  Yes.

• 20:05Matt Kirshen?

  He's also part of NASA.

• 20:06Janna Levin?

  Yes, and part of the experiment was the brother stays on Earth and the other one goes to space.

• 20:10Matt Kirshen?

  Which was a thought experiment from decades back.

• 20:13Janna Levin?

  Insane. And, I mean, he had many more physical effects that were much more important than the time dilation, but basically he aged more slowly than his brother. But, you know, they're not going to notice, but if you interstellar travel, you're going to come back and, and let's say Scott Kelly goes and interstellar travels and comes back and then his brother is really, you know, maybe 70 years older and he's a couple of years older.

• 20:38Matt Kirshen?

  That is a, okay.

• 20:39Janna Levin?

  So that's scary.

• 20:40Matt Kirshen?

  That's a great answer.

• 20:41Janna Levin?

  That's the scary part.

• 20:41Matt Kirshen?

  That is a great answer.

• 20:42Janna Levin?

  Yeah.

• 20:43Matt Kirshen?

  From Jay-Z McGovern on Twitter, "What is hyperspace and how does that differ from warp?" Asking for a friend, says Jay-Z.

• 20:52Janna Levin?

  Um, okay.

• 20:53Matt Kirshen?

  Not having it, Jay-Z.

• 20:54Janna Levin?

  If this is like-

• 20:55Matt Kirshen?

  You own it. You own that question.

• 20:56Janna Levin?

  If this is like a game show and I'm allowed to reach for Lifeline, I'm allowed to pipe this back to you because you're the popular culture guy. I hardly know what year it is. Like, I'm surprised I know what day of the week it is, right?

• 21:11Matt Kirshen?

  That's right. You live in a world of dimensions and figures and-

• 21:13Janna Levin?

  So as the pop guy, I think you have to tell me what hyperspace is.

• 21:18Matt Kirshen?

  I, I, I think, I'm pretty sure the only difference is the science fiction franchise that the words have come from. Because I don't, I, they're, I, I'm pretty sure. I'm, I'm, I think we're just talking Star Wars and Star Trek.

• 21:35Janna Levin?

  Do you have stock in any of these franchises?

• 21:37Matt Kirshen?

  No, I, I don't. And also, I'm not good on pop culture either, but-

• 21:40Janna Levin?

  Well, I think hyperspace, I think what they probably mean is extra spatial dimensions. Should we just assume that that's what they mean? I don't know. Can we opt to answer whatever questions we want?

• 21:49Matt Kirshen?

  I, I honestly think they're just two different ways that different sci-fi things have used to describe going faster than light.

• 21:54Janna Levin?

  But you know what? Sci-fi, sci-fi can be very provocative in terms of generating ideas.

• 21:58Matt Kirshen?

  Right.

• 21:58Janna Levin?

  So I'm not dissing sci-fi. And, but I'm going to answer the, the extra spatial dimension question because I can. Is that fair?

• 22:06Matt Kirshen?

  Yes, go for it.

• 22:06Janna Levin?

  So it's completely possible we live in extra spatial dimensions. I work on this as a serious science project, science thesis, that the universe has more than three spatial dimensions and that it's an illusion. Because every day, we do this experiment where we live in three dimensions. Every day, around the world, billions of people confirm this experiment. There are three spatial dimensions. But it actually could be an illusion. And so, one of the interesting possibilities is that something like dark energy is actually a quantum energy trapped in extra spatial dimensions that are just very, very small.

• 22:40Matt Kirshen?

  Well, isn't extra dimensions also one of the reasons, one of the things that's positive is the reason why gravity is so much weaker than all the other forces?

• 22:48Janna Levin?

  Yeah, so it's a very clever suggestion by a bunch of theoretical physicists, like Nima Arkani-Hamed, Lisa Randal, Demopoulos, DiWali, a lot of interesting people worked on this, that it's like you've diluted gravity over this huge volume. Even though the extra dimensions are small, they're kind of everywhere, right?

• 23:10Matt Kirshen?

  Because gravity is...

• 23:11Janna Levin?

  And so, it makes it very diluting. Like, if you ask, "Which direction is up?", right here, there's up. But if I go a little bit over, where's up? It's right here. So the dimension up exists everywhere.

• 23:23Matt Kirshen?

  Okay.

• 23:23Janna Levin?

  Do you know what I'm saying? So those extra dimensions similarly would exist everywhere. If I was right here, I'd be like, "Where's the extra dimension?" Well, I can't really point to it, but it's at every single point in space, there's that extra dimension.

• 23:34Matt Kirshen?

  This could theoretically explain why a tiny magnet can override the gravitational pull of the entire Earth.

• 23:41Janna Levin?

  Yeah, because the argument would be that the electromagnetic force, which is responsible for the magnetic pull, is bound to three dimensions. Maybe it's glued to a sticky brain, which is a membrane which lives in three dimensions. But gravity has to live in spacetime. However big spacetime is, that's where gravity has to live.

• 23:59Matt Kirshen?

  Which is why it's...

• 23:59Janna Levin?

  It is equivalent to spacetime. So gravity doesn't have the option to confine itself to a smaller space, so it kind of blobs out. And as a result, it actually makes it, it dilutes the strength of gravity. Yeah.

• 24:11Matt Kirshen?

  How widespread is that?

• 24:12Janna Levin?

  Why would you know this weird?

• 24:14Matt Kirshen?

  I don't know. I don't know where that little thing.

• 24:16Janna Levin?

  Come up with this kooky knowledge.

• 24:19Matt Kirshen?

  But I do know that gravity is incredibly weak compared to electromagnetic force.

• 24:23Janna Levin?

  It is incredibly weak. It's something like a trillionth of a trillionth of a trillionth. The strength between two electrons gravitationally versus electromagnetically.

• 24:33Matt Kirshen?

  Well, that conveniently leads us straight into the next question from ADVed on Instagram. What kind of gravitational force exists in space such that smaller bodies revolve around the bigger bodies and not fall upon them?

• 24:46Janna Levin?

  Oh, well, I can put an apple into orbit just by throwing it fast enough. So the International Space Station is traveling at 17,000, over 17,000 miles an hour, I think it is. Maybe Lindsay over there has got a little fancy machine where she can, I don't know, connect to space and find. But I think it's over 17,000 miles per hour. And if it was going slower, it would drop to earth like a stone.

• 25:12Matt Kirshen?

  Right.

• 25:12Janna Levin?

  Okay, so it's not about sizes of bodies. It's about how much you fling them. You know, so if I take an apple and I drop it, it goes straight to the earth. Bang, splat. If I throw it, it travels a little bit further on an arc. If I throw it at 17,000 miles per hour, I could put that thing in orbit.

• 25:29Matt Kirshen?

  Right.

• 25:30Janna Levin?

  Right, at happy apple. Doesn't matter how big it is.

• 25:32Matt Kirshen?

  How is that experiment going? How far have you got it so far?

• 25:35Janna Levin?

  I've gotten like not to the wall. You see the apple splats progressively?

• 25:40Matt Kirshen?

  It's a big room. It's a big room and that's impressive and I really.

• 25:43Janna Levin?

  These are our beautiful new science studios, which we are proud to have renovated with support from the Simons Foundation.

• 25:49Matt Kirshen?

  Good plug. Good getting in the plug in the middle of that.

• 25:52Janna Levin?

  I didn't, I didn't even think I was gonna get a plug in. I didn't, it occurred to me. I should have thought of that sooner.

• 25:57Matt Kirshen?

  Okay, Holly Anne Lang on Instagram. When you're traveling in space, do you feel the effects of time dilation as you move closer to strong gravitational forecast?

• 26:07Janna Levin?

  Love this stuff.

• 26:08Matt Kirshen?

  Does the G-force affect your experience of time?

• 26:10Janna Levin?

  Okay, so here's something that took me a very long time to struggle with studying relativity. Your experience of time is unchanged. You don't notice that your time is dilated relative to somebody else's time. And that's really interesting. So literally, if I am falling across the event horizon of a black hole, like what could be worse than that?

• 26:34Matt Kirshen?

  Right.

• 26:35Janna Levin?

  I

• 26:35Matt Kirshen?

  Which is about as strong gravitational pull as you can find.

• 26:38Janna Levin?

  Like if it's dark, yeah, the strongest, right, except for the interior, which is your worst fate, which you're, you know, impending fate. You would absolutely, nothing you could do would let you know that your clocks were acting in any way funny at all. You would feel totally normal, and this is something that people really struggle with. They think if your time is dilating, that you experience it in a strange way, but you don't. You think it's absolutely normal as you're crossing the event horizon. You're looking at your clock, you're looking at your watch, whatever, you know, you're juggling. I don't know what you're doing, there's no gravity, forget it, you're not juggling.

• 27:13Matt Kirshen?

  Well, you could juggle quite impressively because just by placing each ball in the air and then picking it out in a triangle.

• 27:19Janna Levin?

  Exactly, because you're free falling, you're free falling, like the astronauts on the space station. But it's only when you compare to somebody far away that you realize like, oh wow, something weird's going on. They're going really slowly.

• 27:30Matt Kirshen?

  So when we're comparing our Kelly twins, our twin astronauts.

• 27:33Janna Levin?

  Yeah.

• 27:34Matt Kirshen?

  Each Kelly.

• 27:35Janna Levin?

  You have to compare them, otherwise.

• 27:36Matt Kirshen?

  Each Kelly thinks that the time is perfectly normal, and so only when they re-meet up and realize that one of them is decades older than the other.

• 27:42Janna Levin?

  Yeah, it's, nobody gains extra time, it's not a way to get more, squeeze more life out.

• 27:47Matt Kirshen?

  Right.

• 27:47Janna Levin?

  Okay, it doesn't work like that, your experience is totally normal. No matter what, and then you've got about a millisecond before you're crushed to death in the center of the black hole, so that's not good.

• 27:57Matt Kirshen?

  Yeah, can, well, is it possible to skirt the edge of a black hole, just skirt the event horizon without falling in?

• 28:03Janna Levin?

  It's pretty hard, it's pretty hard, it's the same, exactly the same argument as we made earlier about inertial mass. Is that it requires like a tremendous amount of fuel to boost you out of it, right?

• 28:16Matt Kirshen?

  But it's still just like your, it's still your apple going around the earth problem, it just needs to be going quicker, right?

• 28:22Janna Levin?

  It's just an engineering problem, as one of our earlier questions read, so like to get off the earth. I can't remember the number. I feel like it's 200 and I don't know, it's maybe 20 kilometers a second. I don't know, the escape velocity from the earth, something. I don't remember the exact number. But if you're getting closer and closer to the black hole, your escape velocity, how fast you need to be moving. So you have to accelerate until you reach the speed, becomes closer and closer to the speed of light.

• 28:47Matt Kirshen?

  And the closer and closer to the speed of light.

• 28:49Janna Levin?

  The closer, the harder it is to accelerate, exactly. And the more inertial mass, you know, the more inertial resistance you're going to experience. So, so it requires just more fuel than exists in the entire solar system to boost a postage stamp off the event horizon, basically.

• 29:06Matt Kirshen?

  So I've got a question for you. So you're, you're near the black hole.

• 29:10Janna Levin?

  Yeah.

• 29:10Matt Kirshen?

  You're accelerating faster and faster, closer and closer to the speed of light.

• 29:13Janna Levin?

  Yeah.

• 29:14Matt Kirshen?

  Due to special relativity, as you're doing that, you become heavier and heavier.

• 29:17Janna Levin?

  Yeah.

• 29:18Matt Kirshen?

  But that's your weight, not your mass, right?

• 29:21Janna Levin?

  Yeah.

• 29:22Matt Kirshen?

  Your mass doesn't, so like, because the gravitational pull between you and the black hole is proportional to your, your combined masses. But your gravitational pull to each other doesn't increase as you get faster, right? It doesn't?

• 29:36Janna Levin?

  Well, no, it's not that it increases when you get faster. It's that you would be better off just turning off your rockets and falling in.

• 29:42Matt Kirshen?

  Right.

• 29:42Janna Levin?

  And letting gravity do the work for you. And we do that in the solar system. We use slingshots, like we slingshot past Jupiter to send probes faster than they were going when they passed the planet by using gravity to our advantage. So if I were you and you really wanted to go into that black hole, just turn off your engines and fall.

• 30:03Matt Kirshen?

  That is actually a question the nerdy dolphin on Instagram actually asked. Also, Jack from Australia, it says underneath that, will exploiting the density of a black hole to slingshot a ship be an effective method, method of travel?

• 30:17Janna Levin?

  Oh, yeah.

• 30:17Matt Kirshen?

  According to you, potentially, yes.

• 30:18Janna Levin?

  Awesome. Awesome.

• 30:20Matt Kirshen?

  Because you would steal a tiny amount of the energy of that black hole.

• 30:23Janna Levin?

  There's so much energy, like if I drop a rock from the Empire State Building, you know, even including air resistance, it hits the earth pretty hard.

• 30:33Matt Kirshen?

  Right.

• 30:34Janna Levin?

  Right? If I take a little piece of atmosphere like cotton candy off a neighboring star and drop it onto a black hole, it's going near the speed of light by the time it splats.

• 30:44Matt Kirshen?

  Right.

• 30:44Janna Levin?

  And it usually only splats because it's bumped into other stuff that's orbiting the black hole, right? And so that creates this incredibly bright illumination. It's one of the brightest things in the entire galaxy that we have to see is the luminosity of stuff dropping onto black holes. So there's tremendous amounts of energy gravitationally just from falling that you can extract.

• 31:06Matt Kirshen?

  But if you're using it as a method of travel.

• 31:08Janna Levin?

  So instead of splatting, if you went on a little bit of a slingshot, just, you know, like it's what we were saying, the person was asking, why do you, why do you go into orbit? It's just because you're, you know, you're not traveling straight down. You're like being tossed. So if you just travel a bit around it and not falling in, you could slingshot and get a lot of energy out of it.

• 31:24Matt Kirshen?

  And you're stealing a tiny amount of the speed that that black hole is moving through space.

• 31:28Janna Levin?

  It's not even that the black hole's moving through space, it's that the black hole literally slingshots you.

• 31:32Matt Kirshen?

  Okay.

• 31:32Janna Levin?

  It's literally, it slingshots you. And, um, and so you're borrowing your gravitational energy that's released when you fall. So like I take a rock from rest. If I let it go, it's fastest right before it hits the ground.

• 31:46Matt Kirshen?

  But don't you lose that, doesn't some of that speed go when you're then moving away from the black hole again? Because it's going to be pulling you back in.

• 31:52Janna Levin?

  Yes.

• 31:53Matt Kirshen?

  So how do you?

• 31:54Janna Levin?

  You still can win.

• 31:55Matt Kirshen?

  Okay.

• 31:55Janna Levin?

  I mean, strictly speaking, you know, something like, you know, the whole pendulum experiment? Like if I take a pendulum?

• 32:03Matt Kirshen?

  Uh huh.

• 32:03Janna Levin?

  Um, and I let it go, I have to trust that if I let it go right at my face.

• 32:08Matt Kirshen?

  Yes.

• 32:09Janna Levin?

  I have to trust that it can't swing faster.

• 32:12Matt Kirshen?

  Right.

• 32:12Janna Levin?

  And hit me in the face.

• 32:13Matt Kirshen?

  Yes.

• 32:14Janna Levin?

  Right? So if I let it go right in front of my face, it will swing away and come back and just, I've seen people do these demos with these huge, huge, um, uh, like bobs that would knock them out, right?

• 32:27Matt Kirshen?

  Uh huh.

• 32:27Janna Levin?

  But they don't flinch because they believe in the laws of physics. It can never come back closer.

• 32:45Matt Kirshen?

  If a black hole carries the possibility of being a wormhole for space travel, what happens to both ends, point A and point B, when two black holes merge?

• 32:56Janna Levin?

  Oh, I think, okay, I think the person is envisioning that inside a black hole is a wormhole. So you get through, you fall through the event horizon. Like, so the event horizon is a region beyond which not even light can escape. So we live outside event horizons by definition. We live over on this side of the one-way window, right? But if you're a fool who crosses and goes to the center of the black hole, maybe you discover in your last microsecond of living that there's a little wormhole that connects to some other part of spacetime. And people have, you know, pontificated about this, but it's very hard to justify or prove. And it's probably not the truth, but it's an interesting idea, right? So I think the person's asking, now two black holes collide, what happens to the wormholes at the center?

• 33:39Matt Kirshen?

  Right.

• 33:40Janna Levin?

  Um, I don't know.

• 33:42Matt Kirshen?

  There's almost-

• 33:43Janna Levin?

  I don't know. I don't know. It's too crazy. It's too crazy a scenario. But it would be kind of interesting, like, maybe they make a third bridge. I mean, I don't know. You have to, in my field, you have to be able to do the math to answer the question. And we can't do it yet. We don't know how to follow the chalk. We don't know how to write down the equations and pursue them to the end, right?

• 34:05Matt Kirshen?

  Can you test to see if those equations are right? Because by definition, you can't see inside an event horizon, right? You can't see anything that's come out of it.

• 34:12Janna Levin?

  You know-

• 34:13Matt Kirshen?

  Or nothing comes out of it.

• 34:13Janna Levin?

  It's a really good question. If I had the equations and I could pursue them to the end, and I told you, this is what I think happens, you could rightfully say to me, "Well, you can't test experimentally, so how can you have so much faith in it?" And I would say, "Okay, fair enough." Like, there are limits, you know, but I can't even do that, right? So we're not even at the point of being like, "Well, experiment's gonna verify or falsify my theoretical work." We're not even at the stage of being able to do the theoretical work, right?

• 34:38Matt Kirshen?

  Now, I've got a backup question to that as well. The event horizon is- The point at which even light can't escape, like even light is going too slowly to

• 34:48Janna Levin?

  Yes, you can actually, like if I was falling across the event horizon and I and I was to flick a flashlight, like just one photon. One photon at exactly the right instant, I could get it to hover right there at the event horizon. There's a funny, funny condition where the light is racing out at the speed of light, as it should. But the spacetime in some sense is like a waterfall falling in at the speed of light.

• 35:12Matt Kirshen?

  So it's like sort of walking up some escalators that are moving at the same speed that they're coming down.

• 35:16Janna Levin?

  Literally, and it's a mathematical solution in Einstein's equations that where a photon hovers exactly at the event horizon trying to get out. That's crazy, but if you fall past it, like if you're if you're behind me, you're like Jenna, wait.

• 35:28Matt Kirshen?

  But you'd never be able to see that photon.

• 35:30Janna Levin?

  You could actually see the photon, but you would it'd look to you like it was traveling at the speed of light because you're falling in at the speed of light.

• 35:37Janna Levin?

  So there's so there's no way for anybody to see it hovering except another photon.

• 35:44Matt Kirshen?

  Okay. Here's my backup question because that was, I think that's far more interesting than what I was about to ask.

• 35:51Janna Levin?

  Your hair is literally standing on end.

• 35:52Matt Kirshen?

  But I'm becoming more like Einstein by the minute, but.

• 35:56Janna Levin?

  Oh, my God, you're gray.

• 35:57Matt Kirshen?

  Is that how it works?

• 35:57Janna Levin?

  You're gray, you have more gray than I last time saw you.

• 36:00Matt Kirshen?

  Everything's changing. Perhaps a marry, marry, maro.

• 36:02Janna Levin?

  My God, your eyebrows, what is happening?

• 36:04Matt Kirshen?

  Anyway.

• 36:06Matt Kirshen?

  But that the event horizon is the boundary for light. But everything else, like a person or a spacecraft or a satellite or even just even a molecule or an atom.

• 36:17Janna Levin?

  Yeah.

• 36:18Matt Kirshen?

  That event, the the horizon for that would be much further out, right? Because that would never be able to travel that fast. So its boundary would be.

• 36:26Janna Levin?

  Technically, again, back to the engineering problem, you can get arbitrarily close and in principle.

• 36:33Matt Kirshen?

  Right.

• 36:33Janna Levin?

  Be able to escape in principle. It might require more energy than exists in the entire universe to accelerate you to escape. So, yes, you could probably define horizons that were more sensibly defined. Like if I used all the energy of the sun, what's the boundary beyond which? Matt can escape the black hole and it would be much further out than the event horizon.

• 36:57Matt Kirshen?

  Right.

• 36:57Janna Levin?

  But in principle, it's the event horizon for everything.

• 37:02Matt Kirshen?

  Sounds good.

• 37:03Janna Levin?

  You're buying it?

• 37:04Matt Kirshen?

  I'm buying it.

• 37:05Janna Levin?

  I can say any old crap right now.

• 37:06Matt Kirshen?

  No, you're saying it with enough confidence and plausibility that I'm fully sold.

• 37:10Janna Levin?

  I'm very confident.

• 37:12Matt Kirshen?

  Well, we've covered it.

• 37:13Janna Levin?

  Are you sorting through the crazy stuff now?

• 37:14Matt Kirshen?

  I'm sorting through this question because we've kind of covered quite a few of these just through chance, through a conversation, like what boundaries set us from achieving the speed of light? Well, you already covered that. That's the amount of energy and the mental you need to overcome.

• 37:28Matt Kirshen?

  If time is relative, can we send a satellite somewhere else to look back in time upon our Earth?

• 37:36Janna Levin?

  Well, we do that already to some extent. It's actually both a hindrance, but also really a gift that the speed of light is a fixed speed because it means that the further away something is, and the longer the signal is taken to get to us, the deeper into the past we're able to look. So it actually allows us to look into the past. So if the speed of light was infinite, we would not be able to see into the past. But we can see the universe the way it was billions of years ago because the light we're collecting now from far away is that old. And so it's like an archaeological record. It's actually spectacular.

• 38:18Matt Kirshen?

  I think this question is asking one level beyond that. And that's like, could we, I believe, I believe this question is asking, and apologies for misinterpreting, but if not, I'm asking my own question now.

• 38:30Janna Levin?

  Yeah.

• 38:30Matt Kirshen?

  If there was some way...

• 38:31Janna Levin?

  I think that's your prerogative as co-host.

• 38:34Matt Kirshen?

  Screw you, questioners.

• 38:39Matt Kirshen?

  If there is some way using, using some kind of warp technology, using some way of wormholes or curving, curving the spacetime itself so we can effectively travel faster than light without breaking the speed of light, and therefore travel further away, I think the question is asking, would it then be possible for us to look back on Earth and see our own history?

• 39:00Janna Levin?

  Oh, I see what you're saying. Oh, I see. That's good. That's a good twist.

• 39:03Matt Kirshen?

  I think it would.

• 39:04Janna Levin?

  No, we can't because we would have to outrace. So imagine the light leaves the Earth. And here we are, a few centuries later, developing the technology to try to go out into space.

• 39:14Matt Kirshen?

  Right.

• 39:14Janna Levin?

  We would have to outrace that light pulse. And we've already established we can't do that. So to see into the past. But there is one trick. If the universe is finite, if it's not infinite, and if the light has to wrap around the space, then we don't even have to go anywhere. We can just sit here on Earth and look out into space at a distant galaxy, and it would be the galaxy as it was in the past because of what we just discussed. But we might be able to realize somehow, oh, man, that's actually an image of the Milky Way as it was in the past because the light wrapped around this finite space over and over again. And then finally, we developed the technology to intercept it. And so, that's the only circumstance I can think of

• 39:58Janna Levin?

  when we could see the Earth and the Milky Way in the past.

• 40:00Matt Kirshen?

  So we could then tune to the right time.

• 40:02Janna Levin?

  You could figure out who shot JFK.

• 40:04Matt Kirshen?

  That was exactly the example I was gonna use. Weird, right?

• 40:06Janna Levin?

  I just shot it.

• 40:07Matt Kirshen?

  But we couldn't... So we couldn't say, okay, the light from... The sun hits JFK and the shooter and flies off into space into the universe.

• 40:20Janna Levin?

  Right, but let's say somebody broadcasts it and somebody knows, and they broadcast it into space out of the Earth's atmosphere.

• 40:26Matt Kirshen?

  That's flying away at the speed of light.

• 40:28Janna Levin?

  Yes.

• 40:28Matt Kirshen?

  Now, that's traveling at the speed of light.

• 40:31Janna Levin?

  Yes.

• 40:32Matt Kirshen?

  But let's...

• 40:33Janna Levin?

  But the light wraps around and it comes back to us.

• 40:35Matt Kirshen?

  But let's say, ignoring that, let's say at some point, we then develop this sort of warp technology where we can bend spacetime itself. So that light has traveled one light year, but then we travel...

• 40:46Janna Levin?

  Okay, so that's...

• 40:47Matt Kirshen?

  Can we travel like five light years in an instant?

• 40:49Janna Levin?

  Okay, so that's a good example.

• 40:50Matt Kirshen?

  And then sort of leapfrog ahead and capture that light.

• 40:52Janna Levin?

  If we could figure out how to manipulate the entire spacetime, even if it was infinite, we could probably figure out a way to bounce the light back to us, right?

• 41:01Matt Kirshen?

  So in theory, we could do that and then have a telescope that could see into the past.

• 41:04Janna Levin?

  Yeah, we could do that, yeah, in theory. But I mean, it's hard to... I think we would have to collude with a civilization that was far away. Because you can't... Even then, it would be kind of impossible to imagine because I would have to send a signal to that distant civilization and say, "The light pulse is coming your way."

• 41:21Matt Kirshen?

  But couldn't we out...

• 41:22Janna Levin?

  Send it back to us, but that signal would have to outrate the light pulse. You see, so it's a pretty sticky territory. We might be able to pre-plan it. Or you know, or you know what? The distant civilization takes it upon themselves without our communication to send it back to us. That's pretty much the way in which it could possibly work.

• 41:39Matt Kirshen?

  Okay.

• 41:39Janna Levin?

  Yeah. So, do we have time for another cosmic query? Oh, we do. Okay.

• 41:44Matt Kirshen?

  All right. Well, this one, we've touched on this a little bit. I think this is the last good question in this list.

• 41:52Janna Levin?

  The others are bad.

• 41:54Matt Kirshen?

  Well, I think there's only one or two other questions, but they're things that we've accidentally.

• 41:57Janna Levin?

  There's no such thing as a bad question.

• 41:59Matt Kirshen?

  They're things we've accidentally already covered during the course of this. But this is something we've touched on, and I'd like to know more about it because it still confuses me greatly. So, how does dark energy and dark matter play into the science of interstellar travel? And I think wrapped up in that question as well is, what is dark energy and what is dark matter? Because you mentioned this briefly.

• 42:20Janna Levin?

  Okay, so...

• 42:21Matt Kirshen?

  And they're two very different things, right?

• 42:22Janna Levin?

  So, dark matter is just a proxy for a form of matter that we don't know what it is. So, it just generically means we don't know what that is, except that it doesn't interact with light. There are examples of dark matter. People make out that dark matter is so exotic. It's not that exotic. There are neutrinos. Neutrinos are dark. They don't interact with light. So, it's not that exotic. But we don't know what is responsible for so much of the universe being in dark matter. It's like a quarter of the energy content of the universe. So, that's why it's a big deal, not because it's so strange for something to not to be dark. It's really invisible. It's not even dark. Light passes right through it.

• 42:56Matt Kirshen?

  Okay.

• 42:58Janna Levin?

  So, and then dark energy similarly is just a vague name for something else that we don't know what it is, but we see its consequences. Like, we see that the universe is accelerating faster and faster, and we have no idea what's responsible, and so we just label it with this thing. The weird thing is that, so let's say dark energy is seventy-some percent of the energy content of the universe, and dark matter is a quarter, you know, twenty-five percent. Why are they in roughly equal proportions? That's really confusing to people. What's the relationship between them? And so, I think that it's one of the great mysteries, because it means that most of what exists in the universe is just like a little bit of residue. It's like a little bit of dirt left over from the Big Bang.

• 43:40Matt Kirshen?

  So, the fact that this thing, dark energy, that we don't really know, and this thing, dark matter, that we have a vague idea of, but can't really detect very easily, are in the same proportions to...

• 43:52Matt Kirshen?

  The energy we know and the matter we know,

• 43:54Janna Levin?

  Yeah.

• 43:55Matt Kirshen?

  they think is probably not a coincidence?

• 43:56Janna Levin?

  Well, it just seems very strange for it to be a coincidence. I know it sounds like, well, what's the big deal? But it's just that the universe is, you know, 14 billion years old. And right now, the energy content in light is like incredibly low by, you know, 100, you know, 10 billion lower. So why is this equal proportions? You know, so, so it is, it is kind of a real question. But I think that the person was asking, how would it relate to interstellar travel?

• 44:26Matt Kirshen?

  Yes.

• 44:26Janna Levin?

  And you could definitely use dark energy for interstellar travel. It's hard to harness dark matter. I mean, it's hard to harness dark energy for sure, since we don't know what it is. But like in principle, dark energy warps space in this spectacular way, right? It can accelerate the universe. When we were talking about warp drive, they're usually based on dark energy. Like, imagine a dark energy that has the opposite effect of the one that we observed. So it pulls things closer. That would be a dark energy phenomenon. Then you do the jump across and then you push it back out again. And so dark energy is warp drive.

• 44:58Matt Kirshen?

  And then you get out on the other side and then you can see who's struck JFK.

• 45:00Janna Levin?

  Yeah. I know. I don't know. But you don't have jet lag when you get back from California.

• 45:04Matt Kirshen?

  That's true.

• 45:06Janna Levin?

  Well, I think it's time for us to wrap up this episode. We could talk for hours. We're probably going to talk for a couple more hours.

• 45:12Matt Kirshen?

  Excellent. I hope so. I very much hope so.

• 45:15Janna Levin?

  You've been listening and watching possibly StarTalk All-Stars. I'm Janna Levin. My guest was Matt Kirshen. Thanks, Matt.

• 45:22Matt Kirshen?

  Thanks for having me.

• 45:22Janna Levin?

  We're going to warp drive you back to California in a microsecond.

• 45:25Matt Kirshen?

  Thank you.

• 45:27Janna Levin?

  Coach, though. I hope that's okay.

• 45:28Matt Kirshen?

  I can deal with it for a second.

• 45:29Janna Levin?

  And in the meantime, we'll see you next time. Salutations from the multiverse.