Clara Moskovitz: I’m here today to talk about time travel. A timeless, dare I say timeless theme of sci-fi, but is it possible? Is it possible that it actually happens?
Lee Billings: No no no no no. (smile). Well… hey. not much. Oh. I’m Lee Billings.
Moskovitz: My name is Clara Moskowitz. Scientific American’s bi-weekly space podcast, Cosmos Quickly.
[Clip: Show theme music]
Moskovitz: We are going to have a little friendly discussion.
Billings: TRUE? I came to throw it away.
Moskovitz: Well, quarrel. Parley. Confab. Lee, why are you against time travel?
Billings: That’s why I love the idea of time travel! And in fact I always do. Like most people, I travel into the future every second of her. I’m not a fan of rather speculative time travel, though, and while it makes for good fodder for his goofy sci-fi story, it’s incredibly distracting in the real world.
Moskovitz: But in practice, we can see how more extreme versions of time travel are possible while staying within the confines of plausible physics. Einstein’s special theory of relativity shows that the speed at which time flows depends on how fast a person is moving.
Billings: Einstein strikes again, what a rogue.
Moskovitz: Even if you’re traveling in a spacecraft near the speed of light, you’ll still experience the familiar second-by-second ticking clock. But an observer back on Earth will see the clock running slowly, like a glacier. To them, you will be traveling through time at a snail’s pace. So when you finally return, to you he was probably only a year old, but to your friends on Earth he could be a century old. So you have just traveled into the future!
Billings: Yes, no one disputes that! We can now even measure this kind of ‘time dilation’ on Earth, using subatomic particles rather than spacecraft. Some of these particles have very short lifetimes and decay almost instantly. However, if you increase the speed significantly, like in a particle accelerator, you will find that it can last proportionally longer. So make this a mystery, Clara: How can you travel to the past?
[Clip: Back to the Future] This is what makes time travel possible. Flux condenser!
Moskovitz: We see – no one has yet figured out how to travel to the past. But the odd thing is that it’s not impossible. Time is one of the four dimensions of the universe, along with the third dimension of space. And we move through space in all directions with no problem, and according to physics, time travel should also be possible as much as possible.
One way people have explored it is via wormholes, the shortcut bridges through spacetime predicted by general relativity. Wormholes can connect distant points in spacetime, meaning that wormholes could potentially be used to bridge the gap not only between here and a galaxy far away, but between 2023 and 1923. To do.
[CLIP: Interstellar: That’s the wormhole.]
Billings: Oh yes, wormholes – the last refuge of villains and desperate physicists. Clara, the problem with wormholes is that unlike the DeLorean, there’s no evidence that wormholes actually exist. And even if it did exist, it seems that the only way to make a wormhole passable and stable is to use negative energy or negative mass to prop it open. . And just like the wormholes themselves, there’s also no evidence that these strange forms of matter or energy actually exist. And once again, let’s beat this dead horse – even if the wormhole exists and there was a means to make it passable, going back in time would be very distorted, like around a black hole. It seems that one end needs to be fixed in the space-time region. Or accelerate to nearly the speed of light. Clara, are you feeling the theme here?
Moskovitz: yeah yeah. All I can say is that just because there is no evidence that these things exist, there is also no evidence that they do not or cannot exist. Wormholes are real solutions to the equations of general relativity, and even negative energy and mass are concepts that come up in mathematics and aren’t forbidden.
Billings: Now, what about a more practical argument? Could someone go back and kill Hitler or at least stop me from wearing that ridiculous outfit to my high school prom? There is a famous story about physicist Stephen Hawking, who invited time travelers to a party he hosted. The trick is that the party was held in 2009, but the invitation came out in a miniseries that aired in 2010. In other words, only time travelers should have been able to participate.
[CLIP: Stephen Hawking Time Travel Party: Here is the invitation, giving the exact coordinates in time and space. I am hoping in one form or another it will survive for many thousands of years.]
Billings: Sadly the hors d’oeuvres were left uneaten and the champagne unopened. Because time travel to the past is obviously impossible.
Moskovitz: I admit that a party with Dr. Stephen Hawking would have been pretty appealing to time travelers if they were there. But you forgot about international confidentiality clauses. Probably every time traveler has to take an oath to ensure that their identity and abilities are hidden from people of previous eras.
Billings: Hmm, yes, there is a confidentiality clause here. It really feels like we’re making a special appeal to the realm of science fiction here. And don’t forget all the contradictions we have to worry about too. There are many good reasons to think that time travel can cause insurmountable paradoxes in physics. The most famous is the grandfather or grandmother paradox. If it were possible to time travel to the past, a person could go back in time and kill his or her grandparents, and as a result, it would be impossible for that person to be born or to time travel to the past and commit a crime. I have an idea that it is possible. murder, etc.
Moskovitz: I suspect it’ll be something of a multi-world scenario where each change the time traveler makes to the past creates an entirely new universe that continues from that point in time. So if I go back in time and kill one of my ancestors, I will start a new divergent universe where the entire descendant, including me, never existed. I mean, as crazy as it sounds, physics is so obsessed with the multiverse that they already seem to be popping up for many reasons. Maybe not possible?
Billings: I don’t think so, if not impossible.
Moskovitz: Well, I’m a perpetual optimist, Lee! Thank you for listening to Cosmos Quickly.
Billings: Our show is produced by Jeff DelViscio, Tulika Bose and Kelso Harper. Our music was composed by Dominic Smith.
Moskovtis: If you like the show, please consider rating it or leaving a review. You can also email us your feedback, questions and tips. Science Quickly @sciam.com.
Billings: For more spacetime secrets and science news, visit sciam.com. It was Cosmos, Quickly. I’m Lee Billings.
Moskovitz: My name is Clara Moskovitz.
Lee: See you next time, see you in the future!
