Is Time Travel Possible? Here's What Physics Says.

What does physics say about time travel? Surprisingly enough it doesn't just say it's impossible, it's more complicated than that. In this video I'll sort out what Einstein's general relativity and quantum mechanics tell us about time travel. And is MIT really building a time machine to find dark matter? We'll get to that.

🔗 Join this channel to get access to perks ➜

00:00 Intro
00:20 What do we mean by time travel?
02:51 Special Relativity
04:33 General Relativity
10:07 Time travel paradoxes
12:28 Time-reversal
16:10 New book "Faster than Light"

#science #physics

[SabineHossenfelder]

We have a major upgrade to the quiz app coming up next week, it should be much faster then!

[-by-_Publishing_LLC]

*Time Traveler's Motto:* _"Never do yesterday what can be done two weeks ago."_

[donaldjmccann]

I had a short email debate with Kip Thorne about the possibility of sending information into the past, back in the year 2000, when he was around 60 years old. When he expressed doubt about my proposed methodology, I replied: ''' That's what you told me at your 70th birthday party!'' (He thought that was funny)

[jedwards]

“We’ve already used up our negative energy on Twitter.” Oh Sabine, your humor is so lovable.

[jeffs]

I'm a time traveler from the Past. I travel through time in real time. So far it's taken me 54 years to get to 2024 from 1970. True Story.

[jeffryphillipsburns]

Good. video and on topic. I’m happy that Sapine pointed out that entropy decrease isn’t impossible, just very unlikely. I think a lot that has been said about entropy for general consumption has just confused the public and led to hold entirely erroneous ideas about the subject.. I make it a rule as a music teacher never deliberately to tell a falsehood to a pupil no matter how young or inexperienced or even slow the pupil. Most of my peers make no attempt to observe this rule, and the consequence is that even professional musicians (in fact, most professional musicians) are mistaken about very basic principles of music theory.

[iceman]

"We used up all of our negative energy on Twitter "

Deadpan and spitting facts! I love Sabine 😅

[AICoffeeBreak]

I hope this video untangles all my confusions about time travel. 😵 Otherwise I'll take yesterday to read more about the topic.

[mehguy]

The "reverse entropy to time travel" theory is used in the movie Tenet by Christopher Nolan and it's very amusing that virtually no one used this concept in sci-fi before (if anyone knows of any other examples - please tell me)

[altant]

Great video and the book, thanks for the recommendation. Bought it straight away. The type of the explanations in the book, with diagrams, good questions to engage the reader and articulate on that is one of the best experiences as a reader. And I have read many books on this topic, (and studied astro back in bachelors) and I think this is the most original type of physics book I have read.

[Honkious]

Imagine she actually makes another time travel video next month.

[joshuacornelius]

Sorry Sabine... we HAVE NOT used up all the negative energy on Twitter as human beings are sources of infinite negative energy and all other manner of paradoxical peculiarities. 😂

[mageprometheus]

The video finished at 17:39. I restarted it at 00:00. I'm now waiting for my Nobel Prize in Physics to drop through my letterbox.

5:50 “…and we’ve already used up all our negative energy on Twitter…” I was dying brah. Brilliant video, with killer humor! Keep on rocking Sabine! 😎🚀☀️🙏

[gashery]

Having someone comment your new book with the words "Better than a new particle collider!" has to be a career defining moment.
Thanks for the video!

[fixingyourdystopia]

Sabine, if I were captain of the Enterprise, you'd be my first science officer 😁😉

[Ken]

You mentioned that in theory it is possible to reverse particle interaction. I have always wondered how that can be true in the case of an unstable atom that decays into a spray of resulting atoms and particles. If you reverse that, there is no guarantee that those atoms and particles won't decay, themselves, on the way back, because their life times are also subject to quantum random decay.

[ryanbrown]

Back as a teenager I read Thrice Upon A Time which did the "you can only send a message back to when the machine exists" and the "you can't send stuff, but you can send a signal" ideas. Interesting concepts.

[nyariimani]

Hahahahaha! 5:41 "We've already used up all our negative energy on Twitter."

[mrgalaxy]

I appreciate the effort Sabine puts in to explore other non-physics topics in her videos and to branch out her content, but realistically this is what I'm personally really here for: physics! Esoteric, no-nonsense physics to be precise. So this episode was a real treat and reminded me why I've subscribed in the first place. Thank you for all you do Sabine, you make these mind-boggling topics so accessible to us laymen.

As for the topic of time travel, it's pretty much the typical "in principle it's not forbidden, but practically it's incredibly unlikely and/or we don't have evidence for it". Like all the other fun esoteric topics of parallel universes, negative energy, all kinds of infinities, black hole shenanigans and so on, the theory doesn't forbid it, but we don't have any evidence or even hint of evidence for it so we can't exactly work with it to build a working, practical theory. It's all speculation in the end, but it is impressive how much we've been able to figure out so far. The real question is how deep does the rabbit hole really go and how far along it have really fallen already.