And Logan says, Hello, beloved science professors, and happy holidays from Kansas cities. I'm already giddy waiting for the episode where we get to hear about the knowledge and theories on the topic of time travel. Okay, well, we're in it. Nice. And he says-

And he's hailing from both Kansas cities, Casey Moe and Casey Kansas, I guess. Okay. That's the plural there. Yeah. Right? Yeah. Okay. Okay. He says, if controlled backwards time

travel was possible today, where do you think your matter or information would travel? And no, I'm not talking about what time do you want to travel, but rather if you were in a third person position observing someone travel back in time, what do you think it would look like? So the time travel itself, if you were the observer, what would you see if you were able to observe the timeline itself? So I like

that, but also just slipped in there, Brian, was some mention about information. Yes. And that links to entropy, I presume. So if you can tackle both of those in the next 90 seconds before we

go over the place. I think the only real right answer to that question is to commit to a version of time travel to the past. And the version that I find most convincing involves wormholes. And the idea of a wormhole, I think many people know this idea, It's a tunnel from one location in space to another location and pays a kind of shortcut. And if you move those openings relative to each other, you put one near a black hole, again, there'll be a time difference between the two openings. So now one opening is ahead, one opening is behind. So you go through the tunnel one direction, you go to the future, you go through the tunnel the other direction, you go to the past. So what would going to the past look like? Somebody would enter the opening of a wormhole and they would disappear and they'd pop out the other opening of the wormhole at a different place at a different

time. So in the Marvel universe where you have Doctor Strange opening these portals, he's only moving through space. He's not actually moving through time. So that's a lost storytelling element there that they could totally do interesting things with, it seems to me.

Yeah, I mean, the richness of wormholes really arises when you have a time difference between the two openings. I mean, it's fun to have a tunnel through space, but it is mind-blowing to have a tunnel through time. And also, I

would add that, I think I can add correctly, Brian, that as portrayed in the movie Contact, where Jodie Foster goes through this, we presume, is a wormhole to get to visit the aliens and then she returns. We like the idea that it's like a water slide. You know, you're in this tunnel. You're in this tube and you're sliding. But it's really just a simple hole. You step through it, right? It's not some journey. Isn't that correct? Because they're basically in the same place.

They can be, but you can also have situations where the throat of the wormhole has some length to it. And then again, it would just be traveling through space. It wouldn't be some kind of, like you say, water slide or some kind of weird thing that was happening.

But you're right. Okay. So, all right. So, if you're going to do this, at least and report on it, if you're in a wormhole and it's propped up nicely and it's safe for you, then you're just moving through space backwards in time if the opening of that wormhole is near a black hole

where time is ticking more slowly than where you came from. Or if it was there for a while. Once you set the time difference between the two openings, you can then move away from the black hole. Right. Because the time difference will then persist. Wow. Jesus. That

is insane. So Chuck,

in this one broadcast, you've mentioned God and Jesus together. Yeah. This must be a very significant force operating on your brain right now. Instead, I should have

said, Father Time.

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All righty, here we go. This is Jim Kelly, and Jim Kelly says, Hi, Dr. Tyson, Dr. Green, Dr. Comedy. Why do physicists assume that all time travelers are murderous, patricidal maniacs? Just kidding. Just kidding. But how does a hypothetical paradox preclude the existence of time travel? Yeah,

I mean, I don't think it does. So the hypothetical paradoxes are you change the past in a way that, say, prevents your own existence. And we already discussed how maybe you can't do that. mention of is if instead of traveling to the past in your own universe, the laws of physics demand that you go to the past in a parallel universe. Well, if you prevent your own birth in that universe, there's no paradox. Where were you born? In a different universe. And so that's another way in which you can have the freedom to make changes to the past, but not the past of your own world.

And that's what the Marvel Universe persistently does. That's how Spider-Man can have multiple origin stories, for example. Yeah. We're actually accessing a different universe where similar things are happening, but not so different that we don't recognize the story. That's crazy. So, Brian, what about information? Because information, I don't think it has mass, does it? Does it travel? Information is this intangible thing. And I always hear physicists arguing about whether we lose or gain information every time you do something with a black hole. Yeah.

I mean, I like to think of information as more concrete than that description might suggest, because information is always carried by particles. You can have an abstract measure of information, but if you want to look at the motion of information, it's got to be the motion of stuff that carries that information. And to me, that makes it much more clear what's going on. So with black holes, the whole question was, as radiation comes out of a black hole, which Hawking, Stephen Hawking, told us will happen, are the particles... Instead of Hawking, you mean Stephen Hawking? That's right. That's right. They always get those confused. Different universes. That thing I'm specifying, Brian, which Hawking you're referring to. There was a universe where Hawking actually was responsible, but let's put that to the side. Question is, do the particles have a relationship among each other that carries away the information of what fell in? So it's really concrete when you think about it as information carried by stuff.

Okay, because, right, because otherwise there's no information without stuff to carry it. Right. That's another way to say it. It's hard

to follow the information without that commitment.