The quiz for this video is here: quizwithit.com/start_thequiz/1697148954345x743164650631523500 We have a major upgrade to the quiz app coming up next week, it should be much faster then!

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

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

I'm a time traveler from the Past. I travel through time in real time. So far it's taken me 53 years to get to 2023 from 1970. True Story.

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)

"We used up all of our negative energy on Twitter " Deadpan and spitting facts! I love Sabine 😅

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.

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.

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.

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)

Imagine she actually makes another time travel video next month.

Sabine. Your channel is my favorite regarding scientific topics. I like that you get in depth without to much complexity to us, the average viewers with many topics that are presented, which is the contrary case as for other science communicators such as Kaku or NDGT as they just say this is like this just because.

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.

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.

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.

How about a particle entangled. One particle in the past and one in the future. One changes and the other charges as well. There you have it faster than light change. (Travel)

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!

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

Negative energy=Twitter/X😂

Oh my goodness! I just discovered you... and I clicked subscribe 10 seconds in... You are so good at what you do! I will have to binge all your videos now. GREAT STUFF!

I liked the video,it is very well structured and inspiring. Excellent recap on all possible ways of time travel.

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. 😂

Hi Sabine! Thanks for the awesome video! Not sure if you’ll see this (or perhaps a knowledgeably commentor), but could cosmic strings be another area where closed time loops occur? Thanks!

Sabine: Great video as usual. Besides the infinities that are needed, I was under the assumption that time travel for matter is impossible due to the violation of the same matter occupying two time-space simultaneously. The passage of information on the other hand is intriguing and more plausible if it does not require matter.

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

Thank you for telling us about Robert Nemiroff's book! I'm always looking for good reading material on Relativity and Quantum Mechanics, and since I grew up in Michigan (and have a friend who went to Michigan Tech), this book has extra, personal appeal. I have already bought the Kindle version!

I’m time-traveling all day! Flying back to Europe from the US works… Finally grazing a superheavy rotating black hole works too!

The talk of spinning black holes reminded me of John Titor, a guy in the late 90's who claimed to be a time traveler and then vanished.

Good discussion on a field requiring fuzzy logic. And then there are the tachyons with their negative time. Thanks

I‘ve been studying for a couple years a wormhole at my favourite bar. Timespace destination seems random, but further investigation is required before any conclusions.

"We just talked about time travel next month." :-)

Was at a lecture by Lawrence Krauss a few days ago, he jokingly mentioned that even if we had a Time Machine it would also have to be a space ship because the earth travels around the sun at 30 km per second and the sun about 200 km per second around the Milky Way. So most likely we would appear a long way from home in that era.

If we send someone back in time, there's no reason to assume they'll appear in the same place on the globe, or even anywhere near the globe. And even if they manage to end up in the same logical place, what happens to the air in the space where they appear?

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

I liked your video very much when I saw it in 3 years!

"and we've already used up all the negative energy on twitter"🤣🤣🤣🤣 brilliant.

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! 😎🚀☀️🙏

Sending just a few bits back in time could have massive computational repercussions. Consider a machine that does part of a computation and sends the partial solution back in time to continue the computation. In principle, any computation that is executable in finite time could be made executable in an arbitrarily small time frame.

One possible usage of time travel of particles (assuming that time travel of particles turns out to be possible) that I'd like to see someday would be net faster than light communication by relaying the messages into the past. That'd make populating the rest of the solar system a lot easier.

Sabine, you are awesome! watched your videos here in year 2089 and your theories are still holding up! awesome!

In the early 1960s, the great science fiction edtor Terry Carr, who was then a struggling writer, wrote a short story titled, "Brown Robert." In it, the titular character creates a suit that will allow him to travel through time. He plans to use it to enact revenge on an enrmy from his past. He sets the suit to arrive three days in the future and activates it, sure that soon veangeance will be his. Three days later, the suit returns, but all that's inside are the remains of our protagonist. He dies within seconds of his arrival because he had assumed that he would find himself on Earth in the future. But the Earth hadn't yet arrived where it was to be, so there was nothing at the end of the jump but empty space. The cold and the vacuum killed him even before the radiation could. People who dream of time travel never take into account that all of space is in comstant motion!

The problem I have with Many Worlds is that an infinite number of alternate realities branch off from each event. It's like a tree with infinite branches. So if time travel were possible, we'd be inundated with time travellers from different realities that can be traced back to an event in our present.

The thing about time travel is it would also have to be travel in space. If you traveled back in time a week and popped out at the same spacial coordinates you would be quite some distance from where you started due to how much the earth, sun and galaxy moved during the interval.

Something that people talking about time travel never mention is the fact that the Earth is moving at several hundred thousand KM per second (when you add together the speed of Earth's rotation/ orbit, the sun's travel through the galaxy, the galaxy's movement, our local cluster's movement, etc.) So if you were able to travel even one day back in time, you would be millions of KM away from the earth in space. Another thing that never gets mentioned is, when talking about the speed of light limit, does the speed limit apply to the individual approaching the speed of light, or to the observer? Speed has as part of its definition time (KM per hour, etc.) If you are approaching the speed of light, your time begins to slow as compared to the outside universe. So if the speed limit applies to the individual approaching the speed of light, then the slower that individuals time becomes the farther past the speed of light it would appear that they were traveling from the outside. As far as time travel paradox goes, once a time traveler had removed themselves from the time stream (meaning having traveled out of time to go into the past or future) they are no longer subject to it. Imagine a record album, with the groove being the time stream. To move to a "past" or "future" song you need to lift the needle up off the record to travel to the new song. If you travel into the past and kill your grandfather, you would not "simply vanish" because you have removed yourself from the time stream. But if you traveled back to the present you would discover that you and your parents no longer exist there, and you would have no official identity, your home and belongings would be gone and everyone who knew you.

6:11 There is the theory of The Mobieus; a twist in the fabric of space where time becomes a loop.

If you create a simulation so accurate down to last subatomic particle would that be recreation

My headcannon for the grandfather paradox is the universe autocorrects itself based on timeline. If your original timeline you were born, and go back and kill your grandfather, the universe would split into different timelines. One where you were originally born, and one where you killed your grandfather and werent born. You would either still exist because it was a different timeline, or the universe would autocorrect itself deconstructing you down to the atomic level to be used elsewhere in space-time

I look forward to viewing Sabine’s weekly videos. They are informative, funny & don’t always follow the well rehearsed narrative. However, I must take umbridge with this video on 2 fronts. 1. Black holes - Isn’t it about time we stopped calling them black holes? A black hole is not a place to enter another dimension or universe or a singularity. In this case a singularity is simply a euphemism for the math is giving us gibberish. If we prescribe to the QFT & all particles are excitations of a given field then a black hole may be visualized as a place where the separation between the excitations is close to or zero. That is ALL. wrt time travel - let’s go I step back & define time. The time we measure with the clocks is the numerical order of events. 2. ALL man-made clocks are affected by gravity, the perfect gravitational clock is a sand clock & that virtually stops as we go up further from earth's surface. i.e. the opposite of what we measure with an atomic clock. The only "real" clock that is reliable is the rotation of earth around the sun. I would bet that if a person was located 10 km beneath earth's surface & was able to live for 1000 years and you compared him to the person living on top of Mt Everest 8.8km above Earth's surface, OR next to a black hole then after 1000 years, they would both be 1000 years old! I will also bet that in 100 years time dilation & warping of time will be considered one of the greatest errors in modern mathematical physics theory. Refer to Amrit Sorli's derivation of Einstein's field equations WITHOUT a time component www.researchgate.net/scientific-contributions/2160836237_Amrit_Sorli www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjq7c-JuoLqAhXUR30KHb3gAXQQFjALegQIAhAB&url=https%3A%2F%2Fwww.preprints.org%2Fmanuscript%2F201912.0326%2Fv1%2Fdownload&usg=AOvVaw2bedH3i9twthXrL5BH43Ga I’d like to add 3 points: 1. I would argue & paraphrasing Amrit that : Time is NOT the 4th dimension of space-time BUT it is merely the duration of motion in space. Time ONLY requires memory & motion! 2. Entanglement only happens in space NOT time p.s. just because one can fit data using a mathematical model doesn't mean that the mathematical model is a valid interpretation of reality. Like my old maths teacher used to say, you can fit anything given enough polynomial variables OR simply, until we can apply Occam's razor all proposed models are just that.

Bought the book. I normally skip sponsor segments but this one was good!

This episode was insane. First time I've taken a quiz voluntarily lol amazing concepts, hope I get to meet you one day Sabine!

This video is capable of time travel, it dilates time and brings us into the future quickly through the power of fun.

This is my favorite video of yours, and that’s saying something! ❤️ Thank you

I really like the quiz! Is there a way to check which questions you didn't understand too well?

How did she know what she talked about "Next Month" .... did Sabine travel forward ?

Not only your shadow can travel faster than light, also your laser pointer can move faster than light across the face of the moon…

The humor is timeless! Bless you Sabine!

I've thought for a long time that we think about the interior of black holes the wrong way around. The effect of time dilation is to bring the t and x axes closer and closer together at a diagonal vs far away where they are closer to orthogonal. At the event horizon, they become collinear. If you continue the process, what happens is a swap of the x and t axes as t continues on past x until they are orthogonal again at the singularity. Taking that seriously, you'd invert the axes in the equation. That gives you a finite, removable singularity. One that stops dead in the local time axis as the rest of the curve evolves in time. It's not so obvious how to do that with potential without a piecewise equation but it's relatively straightforward with time dilation. You can use something like Re(sqrt(1-2/|x|)-sqrt(1-|x|/2)) to visualize what I mean for the Schwarzschild metric. If you multiply the second part by i and remove the Re, you can convert the result to a complex potential (square it, subtract 1, divide by 2) and take the real part of that. The end result is equivalent to the piecewise V=-GM/r for r>=r_S and r/(4GM)-1 for r

Thank you for the video.

We just talked about time travel next month!! 😂 The problem with developing time travel is not physics, it’s language. Once we get the language right, developing the technology would be easier

I can't help but love you. I just can't say exactly what I love more about you...Whether it's your content or your craft. You make physics sounds friendly, when it doesn't seem to be. Anytime I watch you talking physics, l lose track of time...( I TRAVEL AT THE SPEED OF LIGHT) --- since I don't know how much time has passed. I'll keep loving you.

If you "travel to the future" via acceleration you're not disappearing from this space time, it's just that your experience of time has been relative to you compared to everything else. You could be observed the entire time and come back, shake hands with someone and just be younger....in the same space time. The tip of times spear is always the same in my opinion, you can experience time differently but the collapse of the wave function within space time has to happen now, now, now, now, now........ Irrespective of how you have experienced time or are currently experiencing time now is always now in space time.

The fact that you would always need something infinite to go back in time answers the question I've had for a while now: If you want to go back in time; what happens the moment time gets zero, just before you move back in time.

From all the parallel universes I've visited so far, this is the one that is fixated the most on time travel instead of expanding the theories to multiple universes. Note: I may not be able to answer questions as I have a train to catch last week in another world.

Bravo. You are the first person to mention entropy I've heard. For a long time I have thought time travel was not possible because of entropy. Of course what would I know with only a BS and MA in political science and public administration fifty years ago.

The paradoxes come from the sci-fi fantasy of travel backward in time while THE OBSERVER'S time travels forward. For example, if you traveled back 200 years, then you wouldn't exist (yet).

The idea that things can time travel at a small scale suggests to me that things could also travel at a large scale if we had total absolute control over a system. I also read recently it's possible to bias the wave function collapse of a particle, which to me implies it's not truely random.

Sabine, i have questions I do not understand. What is 'standing still'? Where is a spot in space that is moitionless? How do we measure movement with nothing to base our measurement on? i.e. If Earth is moving in a solar system that is moving in a galaxy that is moving a universe and that universe is expanding faster and faster, then where is a place to measure movement from? Where is a place that is 'still'?

You hinted at but missed an extremely important concept: Novikov self-consistency principle In a superdeterministic system, Novikov is absolutely guaranteed. It's a direct consequence from the axioms. In fact, it's a direct analytic synthesis from the superdeterministic axioms.

I wonder if there is a gravity mirror or parabola that an immense space telescope could see our reflection in, looking back in time.

I always thought black holes are strongly related to worm holes. I bet, if humanity survives for long enough, we can find a way to use black holes as worm holes.

"We've already used up all our negative energy on twitter" - whoever writes this stuff is a comedic genius, seriously.

I really liked next month's video, but somehow this is even better!

I had a device to travel in time but each journey took an hour to move 60 minutes into the past.

Sabine, it's seldom I can catch you in an error, but if a person accelerates (proper acceleration) at one g they will experience serious time dilation after only about a year of proper time, no pancaking needed. I'll be putting up a video about this within a few weeks for the tensor calculus course I'm teaching. Nice to see you!

I accidentally found ur channel and wow just wow its amazingly explained . Now i am way too curious

Threading a Rindler cylinder between two Alcubierre drives would have some interesting effects.. I read a paper that used metamaterials to simulate time travel in the universe and they found if you went back in time you would mismatch place and vice versa.

If an object "turns around in time," a normal observer would see two identical objects approaching each other and disappearing upon contact. Sounds familiar...

Honestly anything you conceptionally envision is possible it's just a matter of the how!!!! If you can see it in your mind than it does exist🙂

Loved the opening joke. Reminds me of one of my favorite movies, a time travel movie, one of the characters asks one another character, are you hungry? Im starving, i havent eaten since later this afternoon!

Well, two things I know to be true are: 1. Time & space are an illusion 2. You can not go backward in time I'm curious if high velocity travel even decreses your travel through time. What if it's merely changing the rate of vibration of atoms; thus, causing a clock to calculate vibrations slower.

I've long thought that the movie version of time travel couldn't happen without the time machine also being a space machine. Eg. Going back in time 10 minutes from your lounge room in a time-only machine would have you appear in space where your lounge room will be in 10 minutes (followed by a crash and burn into the earth). Solving that issue would probably need faster than light travel. Seems unlikely.

Time travel forward exists: it's called sleep... Time travel backwards would mean duplicating fundamental particles, because most the stuff that composes your body is there since the BB.

This is the topic the reason I subscribe to you Sabine. Please make more videos like this 😘😘😘😘😘😘

13:17 if we use maybe say resonate frequency and used something like a music to diagram a pattern we could make a machine that we could use to change entropy.

Sabine giving the people what they want, more videos on edge science!

Astrophysicists just seem to be the nicest people. Thank you for the education and facts about time, Sabine.

I want a poster of that hour glass graphic. It was beautiful. I hope it's as mesmerizing scaled up.

wow... that was an unexpected yet genuinely fascinating (and highly relevant) sponsor

Time travel talk is all about the clickbait.

Time travel is possible. The video came out 60 seconds ago and it already had 16 likes

Thanks for covering subjects like time travel.

That Twitter joke had me on the floor laughing. fantastic video.

The key thing in this discussion seems to be the idea of causality. Is causality a hard requirement in current physics theories? Or is it merely an artefact of the fact that time travel is not something that occurs regularly in nature? I prefer the interpretation of causality as: cause always precedes effect, moving forward in time. So: if you travel back in time and kill your grandpa… nothing happens to you. Cause and effect only travel forward, your parent and yourself are never conceived, but you are still around because nothing *in your past* causes your un-being. No paradox, no violation of cause and effect.

A lot of the science in this video sounded like something right out of Steins;Gate. I love it, thanks Sabine!

From what I've read, if there were two time dimensions, closed time loops would be possible. Also, I keep on thinking whether we thinking we live in a 3+1 spacetime instead of a spacetime with more dimensions is because in of those time dimensions we might be traveling at the top speed so we do not experience one of the space dimensions and one of the time dimensions just like photons do not experience the dimension through which they are traveling (it is like time has not passed and the length of the travel is shortened to 0 due to length contraction). For me, it is far more sensible to think of a 4+2 spacetime in which one of the time and one of the space dimensions are contracted to 0 than to think of one single time dimension but several space dimensions, many of them being curled (at least from an Occam's razor perspective). Besides, multiple time dimensions is not something we are unfamiliar with. Inside a black hole, the 3+1 spacetime becomes a 1+3 spacetime. Some people seem uncomfortable with the fact that two time dimensions would break causality, but couldn't we just be taking causality for granted like we used to take absolute time and simultaneity of events for granted in the past?

>Sending a few bits into the past Reminds me of "Anathem" from Neil Stephenson

The SCP universe has a fun take on a time machine. The SCP foundation contains anomalous objects, one of them is a device that can send messages to the past and receive them from the future, with messages being more distorted the further in time they traveled. The Foundation has received 3 or so distorted messages from the far future via the device, and while they weren't able to discern what was meant they decide that the device must never used since they reason as long as the machine hasn't sent those three messages then there is still someone alive to send them.

I love how Sabine implies that time travelers from the future wouldn't know who the sponsor is. ( By the way, I bought the book. ) Because if they did, I'd mean that closed time-pike curves on macroscopic scale only bring you back where you started, confining you to a region of space-time where you cannot influence anything beyond your original light cone, the one from before your jump. 🤷🏼‍♂️

Imagine building a time travel machine that randomly dropped you into the void of space in between galaxies. As you appear in that location in space the visible galaxies instantly shoot away from you due to dark energy expansion. At that point you realize you screwed up and you are lost forever.

I didn’t come from the future but would like to go back in time to ask my uncle a question. He taught mathematics to school children in Alaska so he was fairly unavailable to me in Missouri. But he one time said his favorite theory was the second law of thermodynamics. At the time (probably 1980’s) I didn’t think to ask him why and thought I could look it up. But then I tried to find information that would be for non-math types, well I only took college algebra. But I have not found a possible reason till now if it is related to time travel as you mention. And I assume the second law relates to entropy? So if you have a reference book about the second law that would be readable for a person such as me please reply! Thanks! I love your talks and not just because of your accent. 😂