Traveling Through Space and Time, with Janna Levin

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Jana Levin
Welcome to Startalk, your place in the. Universe where science and pop culture collide. Startalk begins right now. Welcome to Star Talk all stars. Hi, Matt.

Matt Kirschen
Hey, Jana. I am your all stars host, Jana 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. Thank you.

Jana Levin
But his role here is just to, like, be my pal today. I want to know how you end up on the all stars. Like, how does this work? Yeah, I don't know. How did you end up on the all stars?

Who selected you? 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. I think I selected you.

Matt Kirschen
Well, I appreciate that. 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 I have. By the world, you mean the west to the east coast of America?

Jana Levin
Isn't that the world it is? As far as baseball is concerned, it's the World Series. If only we could, you know, control time, then it would all be so much more relaxing to have this conversation. Well, there may only not be questions about that right now. Oh, my gosh.

Really? I don't know. I had no idea. What do we got? Well, these questions, these are all themed.

Matt Kirschen
The hashtag was CQ. Interstellar travel. I think the CQ is cosmic query. So it's just the interstellar travel bit. I should have known that lingo.

Right? I feel a little slow. So everything here is interstellar travel based. Manus on Twitter says, unless we come up with a way to rip spacetime work, brackets, wormholes, et cetera, it's not going to happen. Am I right?

Jana Levin
Is Manus right about temporal travel? Well, about space travel, I think specifically. 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 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. It doesn't require technology. So that doesn't contravene the rules of physics, the laws of physics as we know them. It's really disturbing.

But the laws of physics, as Einstein set them down, allow for time travel. And there's a couple of circumstances that occur naturally, but not in our universe. So Godel, the famous mathematician, knew that there was a rotating space time. Like, if the entire universe was spinning, which is not our universe, right? So it's not going to be us.

But if the entire universe was spinning, that he could find a path, a world line, 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 Godel found the solution, but didn't disbelieve it, understood that it was. It was allowed, and his theory was very concerned. But then, didn't Godel also starve to death because his wife went to hospital?

Yeah. So, you know, so that happened. But. 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.

Yeah, you can. Yeah, you can feed yourself. So, I say we're pretty much equal. Yeah. You know, it's.

You know, nature gives greatness and weakness in equal measure, and that's a lot. And we're all about average. All right? We're all about average at the end of the day. So, interstellar travel, is that going to be possible without something like wormholes?

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? Barely. Barely out of the solar system. It's the first interstellar probe humans have ever sent, right?

And 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 it at the Large Hadron Collidere 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 space time 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? Right. Like, the way North Korea is looking. So we're likely to blow ourselves up before. Yeah, I got you.

Yeah. Well, that's a dark. So, Neil Cochrane on Twitter asks if we can achieve the speed to explore the universe. Isn't inertial dampening going to be an issue? Inertial dampening?

Matt Kirschen
What is inertial dampening? Dampening really only matters. Well, I guess it matters anywhere because there's gravity anywhere. So it's hard to push a car, but it's easier to push me around. Right, right.

Jana Levin
And that's because I have less inertia than the car. But in completely outer space, it's not that expensive to push anything. Right. It's really easy. It's really quite easy.

But f equals ma, you know, Newton's laws. Oh, my God. I said an equation in audio. But everyone knows f equals ma, and if they don't, they're going to 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 do it down here on earth.

Matt Kirschen
So you just surely whenever you're moving anything across space, you just need as much deceleration as you have acceleration. Yeah. On the other end, 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, but once it's going, like, I can pretty much just kick back and it's gonna go forever. 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.

Jana Levin
And, you know, if I get something launched in interstellar space, it'll keep going for a long, long time. I see you reading. I am reading. Are you looking pensive? What are you doing?

Matt Kirschen
I am reading. So, Marco Pedroso, do I get to. Ask you some of these questions? Yeah, throw these questions at me. Professor of astrophysics.

Let's see how the idiot comedian pairs.

Jana Levin
Come on. You have a degree in maths? I do, but I scraped my way through it, and that was well over a decade ago, and I have done nothing with it since. Apart from creating a podcast that tenuously has science in the title. It's only probably science.

Matt Kirschen
That's why we put it in there. It's only definitively science. It was named very carefully. The only thing we do carefully on that show. I've been on that show.

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

Jana Levin
To the rest aren't like, is he implicating the others? Yeah. Or other things who, like, 30 seconds earlier pressed, send. Every other question you're getting is bullshit. But this one this one's honest.

Well, my answer may or may not be, depending. Yeah, so, honest question. Ships navigating deep space should be shrouded in total darkness, right? Well, I mean, except for the light from the galaxy. That's not total darkness.

What's deep space? Galactic space. I don't know what count. It would be pretty dark. 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 galactic and that's pretty dark.

Matt Kirschen
Yeah, but then you would still have. If only on the first clause. He's got a comma here. There's more coming. Wait, he would have what?

No, that's 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 can we write him back and ask him what he means?

I don't know. I mean, it's an honest and ambiguous question. If it's interstellar, it's dim. If it's intergalactic, it's really pretty dark. But you are still getting the light from millions of galaxies.

Jana Levin
Sure. But each of those is just a pinpoint, like a single star, right? Yeah. Like if you were a planet, a rogue planet that had somehow been ejected from the galaxy, which I'm sure happens. Right.

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. Right. And it gets thrown. Possibly unlikely, but possibly completely out of the galaxy.

So the whole solar system's floating intergalactic. And takes us with it because we're just still traveling in this wake and it's gravitational. Yeah, it's actually. It's probably kind of normal for us because the sun's still illuminating us, right? So we'd have to lose the sun.

Matt Kirschen
Okay. Okay, so let's say we make up some scenario where some evil genius ejects the planet and sends it intergalactic.

Jana Levin
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. Yeah.

Matt Kirschen
Or the light to see anything. Or the light in your locality. Right, exactly. There wouldn't be enough light coming from these galaxies or stars to then bounce off things and illuminate. Right.

Jana Levin
But imagine, like, the decrease in light pollution. I was just thinking that that would probably be a great way to stargazing. Great stargazing. Seriously good astronomy. Because right now we're in New York City, which has to be one of the worst places in the world for light pollution.

Matt Kirschen
Right. 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. We're looking at Manhattan, which is way, way over there.

Jana Levin
And there's not a lot of. There's not a lot of streetlights or a lot of light pollution around here. We actually have pretty good viewing. That's pretty good. I live in Los Angeles most of the year, and that's terrible.

Matt Kirschen
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. Yeah. Yeah.

Jana Levin
I mean, strictly speaking, Los Angeles is a desert. It is. I don't mean that as a jab. I just mean that literally. Technically, it's a desert.

Matt Kirschen
And you sometimes forget that because you're surrounded by the trappings of non desert, like, a lot of grass that has been expensively imported, palm trees, which have been imported with a lot of unnecessary water usage. And you forget that. And then you go out from the. Water and you're looking down so much that you forget to, like, look up at the sky. Yeah.

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

Jana Levin
Any questions about hydration? Yeah, throw them away. Remember to tag them. Cq Matt's hydration tips. Okay, so we're onto our first Instagram question.

Janna, does it come with a picture? Can I see it? It doesn't. It's just. It's just text rishy.

Matt Kirschen
Rishe on Instagram asks, traveling at light speed is now just an engineering problem. Care to explain? 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 because it's. Or this is just something that Rishi. Rish has read because in quotes, it says, traveling at light speed is now just an engineering problem. Close quote. I'm going to actually back him up on this.

Jana Levin
So there are these nanosatellites that are like the size of a postage stamp that they want to put, like, a couple of computer chips on and send into space, and they're going to kind of laser them, like, accelerate them with the pressure of a laser. And they think that they can get them to light. Very nearly light speed, meaning a fraction. Like, even if it's 0.1 the speed of light. That's really fast.

That's insanely fast. So light speed is 300,000 km/second so you're going 30,000 km/second that's insane. Yeah. 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. This is something I vaguely remember from, this is special relativity.

Matt Kirschen
Right? Special relativity, just straightforward special relativity. The faster something gets, the closer the speed of light, the heavier it becomes, the more inertia it gets. Right. The more inertia it gets.

Jana Levin
And so the harder it is, like, you know, to push it. And so in that sense, it is just an engineering problem. So you want to send postage stamp sized stuff. Right. You can't send astronauts and fuel and rockets, because that, as an engineering problem, is insurmountable at the moment.

Matt Kirschen
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. That's right. So you can get something to some speed.

Jana Levin
Maybe it's a hundredth or a thousandth the speed of light, and it'll pretty much keep going that way, 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 or won't have any particles, just gravitational. Well, that could be a problem. Okay. 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. So how. And you just hope a couple make it. So where is this laser that's going to be powering it?

Matt Kirschen
Going? Turtles? What? Yeah, yeah. So, I mean, that sounds very sci-fi I don't know that much about the technology, but I guess the laser is mounted here on Earth and, you know, light doesn't tire.

Jana Levin
It can make it as far as you can send it and they'll just keep blasting this thing. So I think they recently wasn't there 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 sprinkled it through it. Yeah. And hoped for the best.

So I think they're starting like preliminary ideas on these tiny, tiny satellites. Yeah, that's a. But you could never actually said traveling at light speed. Now at light speed itself, anything that has mass can never reach no light speed, right? 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. The speed of light is pretty good. So I mean 0.1 the speed of light, like we said, that's 30,000 mean, how long did it take you to get from California?

How far away is California? We would definitely. So 3000 miles and it took you 6 hours. I know. Okay.

So you would have gotten here in a fraction of a second and that, that's better. And I think we should really work towards that because you can even deal with economy class in that connection. Are you for that? I could do that. Yeah.

Matt Kirschen
Because even like economy classes. Yeah, yeah. 2 seconds. You know, the boredom of getting on the plane and. 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.

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Matt Kirschen
I'm Jasmine Wilson, and I support startalk on Patreon. This is startalk with Neil degrasse Tyson.

Jana Levin
I'm ready to take more of these cosmic queries. Well, let's go. Did people send us more? They certainly did. At the beginning, I was like, are we gonna have enough questions?

Matt Kirschen
So I was kind of spacing it out, and now I'm like, are we. Gonna get through them? Are we gonna get through them? So Beaucraft on Twitter says, assuming interstellar travel is mastered by humans, what about it excites you? And what scares you?

Jana Levin
Interstellar travel. Well, I mean, what about. It would not be exciting. You know, it's amazing. We would go to it.

We have planets now. We have exoplanets by the thousands in our own galaxy. That is something strange that's happened in the ten years really recent, right. The science of exoplanets has gone from, we might find one to, we can't stop finding these things. 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? Billions. So again, the chance of us finding something approximating, like, life of some way, right? So each one of those systems could have multiple planets.

So that makes more planets than there are stars. And each of those planets could also have moons because, like. 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. We just had something about Europa on our show, and that's the only reason I know this.

Matt Kirschen
But I happen to know that Europa has a lot of water and. Yeah, well, you know, I don't work on anything that happened more recently than a billion years ago, so. Right. Yeah. Your rope is like, this is way into practicality.

You're this stuff for the audio only the people. I'm pointing to a white ball behind us covered in symbols and squirrels. That's the good stuff. Yeah, but. So interstellar travel would mean we could actually go visit these planets.

Jana Levin
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 that's a pretty big sacrifice. That's a scary thing, like the guys who go up to. So I met Scott Kelly today, the astronaut. It was really great hanging out with him, like, for the few minutes. I don't know if it was great for him, but 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. That's right. Scott Kelly has a twin brother who was also an astronaut. Right. He's also part of NASA.

Yes. And part of the experiment was the brother stays on Earth and the other. One goes to space, which was a thought experiment decades back. 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 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 years older. That is a Sc. Okay, so that's scary. That's a great answer.

That's a scary part. That is a great answer. Yeah. From Jay Zmcgovan on Twitter. What is hyperspace and how does that differ from warp?

Matt Kirschen
Asking for a friend, says Jay Z, not having it. Jay Z. If this is. You own it. You own that question.

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

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

Matt Kirschen
I'm pretty sure the only difference is these science fiction franchise that the words have come from.

I'm pretty sure. I think we're just talking Star wars and Star Trek. I think that's all in any of these franchises. No, I don't. And also, I'm not good on pop culture either.

Jana 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? I honestly think they're just two different ways that different Sci-Fi things have used to describe going faster than light.

But you know what? Sci-Fi, Sci-Fi can be very provocative in terms of generating ideas. So I'm not dissing Sci-Fi but I'm going to answer the extra spatial dimension question because I can. Is that fair? Yes.

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

Yeah. So it's a very clever suggestion by a bunch of theoretical physicists like Nima Arkani Hamid, Lisa Randall, Demopolis, 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. Because gravity is. 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.

Matt Kirschen
Okay. Do you know what I'm saying? So those extra dimensions, similarly, would exist everywhere if I was right here. 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.

This could theoretically explain why a tiny magnet can override the gravitational pull of the entire earth. 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 space time. However big space time is, that's where gravity has to live, which is why it's.

Jana 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.

Matt Kirschen
How widespread is that thing? Why would you know this? Weird. I don't know. I don't know where that is.

Jana Levin
I love with this kooky knowledge, but. I do know that gravity is incredible. Incredibly weak. Compared to electricity, it is incredibly weak. It's something like a trillionth of a trillionth of a trillionth.

The strength between two electrons gravitationally versus electromagnetically. Well, that conveniently leads us straight into the next question from ad ved on instagram. What kind of gravitational force exists in space such that smaller bodies revolve around the bigger bodies and not fall upon them? Oh, well, I can put an apple into orbitz 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 Lindsey over there has got a little fancy machine where she can, I don't know, connect to space, and I think it's over 17,000. If it was going slower, it would drop to Earth like a stone. Right? 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, could put that thing in orbit at happy apple doesn't matter how big it is. How is that experiment going? How far have you got it so far? I've gotten. Not to the wall.

Okay. You see the apple splats. It's a big room. Aggressively it's a big room, and that's impressive. And I really.

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Matt Kirschen
When you're traveling in space, do you feel the effects of time dilation as you move closer to strong gravitational forecast? Love this stuff. Does the g force affect your experience of time? Okay, so here's something that took me a very long time to struggle with studying relativity. Your experience of time is unchanged.

Jana Levin
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, right. Which is about gravitational pull, as you. Can find the strongest.

Right, except for the interior, which is your worst fate, which your 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're juggling, I don't know what you're doing. There's no gravity.

Forget it. You're not juggling. Well, you could juggle quite impressively by placing each ball in the air and. Then picking it out because you're free falling. You're free falling like the astronauts in 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. So when we're comparing our Kelly twins. Our twin astronauts. Yeah.

Each kelly have to compare them. Each kelly thinks that the time is perfectly normal, and it's only when they re meet up and realize that one of them is decades older than the other. Yeah, it's. Nobody gains extra time. It's not a way to squeeze more life out.

Matt Kirschen
Right. 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.

Jana Levin
So that's not good. Yeah. Is it possible to skirt the edge of a black hole, to skirt the event horizon without falling in? It's pretty hard. It's pretty hard.

It's 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. But it's still just like, it's still your apple going around the earth problem. It just needs to be going quicker. Right.

It's just an engineering problem is one of our earlier questions. Red? So, like, to get off the earth, I can't remember the number. I feel like it's 200. I don't know, it's maybe 20.

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. And the closer and closer to the.

Speed of light, the harder it is to accelerate. Exactly. And the more inertial mass, the more inertial resistance you're going to experience. So it requires just more fuel than exists in the entire solar system to boost a postage stamp off the event horizon, basically. So I've got a question for you.

Matt Kirschen
So you're near the black hole. Yeah. You're accelerating faster and faster, closer and closer to the speed of light. Yeah. Due to special relativity.

As you're doing that, you become heavier and heavier. Yeah, but that's your weight, not your mass, right? Yeah. So, like, because the gravitational pull between you and the black hole is proportional to your combined masses, but your gravitational pull to each other doesn't increase as you get faster, right? It doesn't?

Jana 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. Right. 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 a 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? 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 of travel, according to you? Potentially, yes.

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

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. Right. 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 but extract. If you're using it as a Methodist 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 go into orbit? It's just because 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. And you're stealing a tiny amount of the speed that that black hole is moving through space.

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

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. But don't you lose that. Doesn't some of that speed go when you're then moving away from the black hole again?

Matt Kirschen
Cause it's gonna be pulling you back in. Yes. So, how do you. You still can win. Okay.

Jana Levin
I mean, strictly speaking, you know, something like, you know, the whole pendulum experiment? Like, if I take a pendulum and I let it go, I have to trust that if I let it go right at my face. Yes. I have to trust that it can't swing faster. Right.

And hit me in the face. Yes. 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 like bobs that would knock them out, right?

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

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Matt Kirschen
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? Oh, I think, okay, I think the person is envisioning that inside a black hole is a wormhole. So you fall through the event horizon. So the event horizon is a region beyond which not even light can escape. So we live outside event horizons.

Jana Levin
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 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? Right? I don't know. 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. Can you test to see if those equations are right?

Matt Kirschen
Because by definition, you can't see inside an event horizon. Right. You can't see anything that's come out of it, you know, or nothing comes out. 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 it experimentally, so how can you have so much faith in it?

Jana Levin
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. 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. 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 hoverdeze 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 space time, in some sense, is like a waterfall falling in at the speed of light.

Matt Kirschen
So it's like sort of walking up some escalators that are moving. Exactly. There's 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.

Jana Levin
But if you fall past it, like, if you're. If you're behind me, you're like, Jenna, wait. And you've been. But you never get to see that photon. You could actually see the photon, but it looked to you like it was traveling at the speed of light because you're falling in at the speed of light.

So there's no way for anybody to see it hovering except another photon. Okay, here's my backup question. Because that was. I think that's far more interesting than what I was about to ask. It's literally standing on end.

Matt Kirschen
But I'm becoming more like Einstein by the minute. But. Oh, my God, you're graying. Is that how it works? You're great.

Jana Levin
You have more gray. I'm growing facial hair. Everything's changing. About to marry. Marry Mary.

Oh, my God, your eyebrows. Anyway. But the event horizon is the boundary for light. But everything else, like a person or a spacecraft or a satellite or just even a molecule or an atom. Yeah.

Matt Kirschen
That event, 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. Yeah, technically, again, back to the engineering problem.

Jana Levin
You can get arbitrarily close and, in principle, 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. Right. But in principle, it's the event horizon for everything. Sounds good.

You're buying it? I'm buying it. I can say any old crap right now. No, you're saying it with enough confidence and plausibility that I'm fully confident. I'm very confident.

Matt Kirschen
Well, we've covered. Are you sorting through the crazy stuff now? Are we sorting through this question? 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 momentum you need to overcome.

If time is relative, can we send a satellite somewhere else. To look back in time upon our earth? 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.

Jana Levin
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. It's actually spectacular. I think this question is asking one level beyond that, and that's like, could we.

Matt Kirschen
I believe. I believe this question is asking, and apologies for misinterpreting, but if not, I'm asking my own question. Now, if there was something like that, prerogative. Yeah, co host, screw you. Question.

Question.

If there is some way, using some kind of warp technology, using some way of wormholes or curving the space time 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? Oh, I see. That's good. That's a good twist. I think it would.

Jana Levin
No, we can't, because we would have to outrage. 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. 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 develop the technology to intercept it. And so that's the only circumstance I can think of. When we could see the earth in the Milky Way in the past, so we could. Then you could figure out how to shot JFK. That was exactly the example I was going to use.

Matt Kirschen
Weird, right? Shot it. But. But we couldn't. So we couldn't say, okay, the light.

The light from the sun hits JFK and the shooter and flies off into space, into the universe. Right? Let's say somebody broadcasts it and somebody knows, and they broadcast it into space out of the Earth's atmosphere. That's flying away at the speed of light. Yes.

Now that's traveling at the speed of light. Yes, but let's. But the light wraps round and it comes back to us. But let's. Ignoring that.

Let's say, at some point we then develop this sort of warp technology where we can bend space time itself so that light has traveled one light year. But then we travel. Okay, can we travel like five light years? That's a good idea. And then sort of leapfrog ahead and capture that light.

Jana 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? So in theory we could do that and then have a telescope that could see into the past. 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. But couldn't we outrage. Send it back to us? But that signal would have to outrace the light pulse, you see, so it's a pretty sticky territory.

We might be able to preplan it. 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. Okay.

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

Matt Kirschen
Well, this one, we've touched on this a little bit. I think this is the last question in this list. The others are bad. Well, I think there's only one or two other questions, but they're things that we've covered. There's no such thing as a bad question.

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, and they're two very different things.

Right. So dark matter is just a proxy for a form of matter that we don't know what it is. So it 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.

Jana Levin
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. Okay, 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, 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 70 some percent of the energy content of the universe, and dark matter is a quarter, 25%.

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. So, like, a little bit of dirt.

Matt Kirschen
Left over from the fact that this. This thing. Dark energy that we don't really know in this dark matter that we have vague idea of, birds we can't really detect very easily. Yeah. Are in the same proportions to the energy we know and the matter we know.

Jana Levin
Yeah. They think is probably not a coincidence or. 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 it is kind of a real question, but I think that the person was asking, how would it relate to interstellar travel? Right. 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 like in principle. Dark energy, warp 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 observe. 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.

Matt Kirschen
And then you get out on the other side, and then you can see who shot JFK. Yeah, I know. I don't know. But you don't have jet lag when you get back from California. That's true.

Jana 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 after the microphone. I hope so. I very much hope so.

You've been listening and watching possibly startalk all stars. I'm Jan Eleven. My guest was Matt Kirschen. Thanks, Matt. Thanks for having me.

We're going to warp drive you back to California in a microsecond. Thank you coach, though I hope that's okay. I can deal with it for a second. And in the meantime, we'll see you next time. Salutations from the multiverse.

E
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Traveling Through Space and Time, with Janna Levin

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1: Introduction to Cosmic Queries

2: The Science of Time Travel

3: Technologies for Interstellar Travel

4: Practical Challenges and Ethical Considerations

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