from the parallel-our-sights-parallel-our-heights dept.
Have you ever made a mistake that you wish you could undo? Correcting past mistakes is one of the reasons we find the concept of time travel so fascinating. As often portrayed in science fiction, with a time machine, nothing is permanent anymore — you can always go back and change it. But is time travel really possible in our universe, or is it just science fiction ?
Our modern understanding of time and causality comes from general relativity. Theoretical physicist Albert Einstein's theory combines space and time into a single entity — "spacetime" — and provides a remarkably intricate explanation of how they both work, at a level unmatched by any other established theory. This theory has existed for more than 100 years, and has been experimentally verified to extremely high precision, so physicists are fairly certain it provides an accurate description of the causal structure of our universe.
For decades, physicists have been trying to use general relativity to figure out if time travel is possible. It turns out that you can write down equations that describe time travel and are fully compatible and consistent with relativity. But physics is not mathematics, and equations are meaningless if they do not correspond to anything in reality.
[...] After working on time travel paradoxes for the last three years, I have become increasingly convinced that time travel could be possible, but only if our universe can allow multiple histories to coexist. So, can it ?
[...] Time travel and parallel timelines almost always go hand-in-hand in science fiction, but now we have proof that they must go hand-in-hand in real science as well. General relativity and quantum mechanics tell us that time travel might be possible, but if it is, then multiple histories must also be possible.
Article written by: Barak Shoshany -- Assistant Professor, Physics, Brock University
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @07:21PM (8 children)
The grandfather paradox is weird even with a multiverse. You go back in time and kill your own grandfather. OK. Universe forks there. It's not hard to imagine the fork where gramps never started your family line. Family lines die out all the time, but now that the universe has forked, what are you?
Right up until the point of the murder, you were some mysterious visitor. You can even be known as a time traveler and it's not weird yet. That singular act of depravity changes it all. Aside from being a felon, what are you now?
The current fork is OK. You're a murderous time traveler. Awful, but sane.
It's when return to the present that it seems odd. You might have told people you were leaving, and that you were going to return. At that point, you're known as the grandson but what returns? Does the grandson return to the original timeline where the murder never happened? That'd work I guess. The dead grandfather fork soldiers on, the current universe unaware. The current is not changed.
So maybe having multiple universes resolves it more easily than I thought, but how does the multiverse "know" to put you in the live grandfather universe?
(Score: 1, Interesting) by Anonymous Coward on Tuesday April 26 2022, @07:28PM
>> how does the multiverse "know" to put you in the live grandfather universe?
The same way that SoylentNews editors know when to post a story twice on the same day... there's some underlying compelling force driving it.
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @08:25PM (4 children)
There is one universe (your original one) where you grew, built a strange device, went into it, pressed a button, and disappeared without a trace.
There is another universe (the fork) where a stranger appeared from nowhere and killed an innocent man with some external resemblance to him.
That's all. No paradoxes.
(Score: 2) by Mykl on Tuesday April 26 2022, @10:34PM (3 children)
Except for the conservation of energy.
The problem with the multiverse is that matter is somehow magically appearing (or disappearing) from the universe. E != mc2.
You could potentially hand-wave the original timeline by saying you return the very instant you left, but you're still left with the problem of having spent some time in the alternate universe with mass that did not previously exist there.
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @11:01PM (2 children)
Conservation of energy is BY DEFINITION totally irrelevant to anything that is affecting time. Because https://en.wikipedia.org/wiki/Noether's_theorem [wikipedia.org]
"invariance with respect to time translation gives the well-known law of conservation of energy"
No invariance - no conservation. Simple as that.
(Score: 2) by Mykl on Wednesday April 27 2022, @05:59AM (1 child)
I will be the first to admit that I'm no physicist, but my layman's reading of Noether's theorem says nothing about matter appearing and disappearing. It appears, to me, to focus more on the net effect of momentum on an object being zero if it is being translated around a central symmetrical (Lagrangian) point. Feel free to make a fool of me if I have that wrong.
If your statement (that conservation of energy is irrelevant to anything that affects time) was true, that would render conservation of energy meaningless, as the 'conservation' part of the statement refers to the state of matter over time. Or perhaps you're saying that objects can appear into a universe from nowhere without affecting the total amount of energy. How? The only way that would be possible would be for an equal amount of energy to be removed from that universe at the same time. If you 'zap in' a planet-sized object, you'd need to remove an equal amount of matter at the same time to keep the total energy the same. How you rotate it is irrelevant.
(Score: 0) by Anonymous Coward on Wednesday April 27 2022, @08:32PM
I think the point they are making is that Noether's theorem says that conservation of energy arises from (or at least is related to) time invariance. If you have a Lagrangian (which is just the kinetic energy terms minus the potential energy terms) that does not have an explicit time dependence (i.e., it is time-invariant), it is pretty easy to take your Euler-Lagrange equation of motion and show that you end up with conservation of energy [ucsd.edu]. So he is saying if you can travel in time, you don't have time invariance, and hence you don't have to be constrained by conservation of energy.
(Score: 2) by sjames on Wednesday April 27 2022, @12:06AM
Two possabilities. You return to the branch where you never killed grandpa and perhaps nobody even believes you time traveled. Or you end up in the other branch where you are still a mysterious stranger.
If we assume some law of nature puts you back in the timeline where your meddling didn't work, perhaps it's due to entanglement? There is one theory that space itself is made of the entanglement of the particles that exist within it.
(Score: 2) by inertnet on Wednesday April 27 2022, @12:39AM
You don't even have to leave your timeline if you could just send a message back to get your grandfather killed. Or send someone else. That way you would never leave your timeline. Would you cease to exist right when you send the message, or won't you even be born? But then your message would never get sent and your grandfather would not be killed. Would that result in an endless loop where your grandfather gets killed and you disappear, then your grandfather doesn't get killed and you reappear again, ad infinitum. Would you realize all this, or do you get stuck in this loop without even knowing? What do the words 'when' and 'then' in these questions really mean?
(Score: 2) by looorg on Tuesday April 26 2022, @07:25PM (1 child)
What would the other timelines be if not parallel to our? That is to say do they even know of any? But if not parallel what would they be? Divergent? Convergent (that is probably horrific)? Perpendicular?
(Score: 3, Interesting) by JoeMerchant on Tuesday April 26 2022, @07:41PM
https://en.wikipedia.org/wiki/All_the_Myriad_Ways [wikipedia.org]
Україна досі не є частиною Росії Слава Україні🌻 https://news.stanford.edu/2023/02/17/will-russia-ukraine-war-end
(Score: 0, Disagree) by Anonymous Coward on Tuesday April 26 2022, @07:37PM (11 children)
Time travel, while a delightful idea, is not possible. Can't go into the future because it has not happened yet. There is literally nowhere to go. Can't travel back in time, either. Where is the past, exactly? It is gone and can't be remade. There is no way to reconstruct the entirety of the universe's state at arbitrary points in time. Not at all satisfactory for us sci-fi nerds but it is what it is.
(Score: 5, Insightful) by maxwell demon on Tuesday April 26 2022, @07:40PM (1 child)
You are stating those claims as facts, but they are just assumptions. The only real truth is: We do not know.
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Thursday April 28 2022, @05:02PM
Say I run a simulation of a universe. There may appear to be a concept of time to entities within that universe but there doesn't necessarily have to be a past to travel to. Unless of course I save some copies...
Of course one could argue that we can't really simulate our particular universe - e.g. stuff like consciousness. Unless of course there's some "magical" property of our universe where just doing some math on a piece of paper can generate consciousness.
Even so I still haven't seen proper proof that there has to be a "time dimension". Time could be a bit like imaginary numbers which make doing various math easier. Just because the math is easier it doesn't mean the imaginary stuff exists for all the stuff that math is used for.
(Score: 3, Funny) by acid andy on Tuesday April 26 2022, @07:42PM (5 children)
Methinks somebody hasn't watched enough Star Trek episodes. Come back when you've watched everything that came out before Enterprise and we'll talk. If you've already seen them all, start again.
Master of the science of the art of the science of art.
(Score: 2, Insightful) by Puffin on Tuesday April 26 2022, @11:09PM (4 children)
Time travel can only mean one thing: the writers of a Sci-Fi serial have run out of plot lines.
(Score: 1, Funny) by Anonymous Coward on Wednesday April 27 2022, @02:08AM (3 children)
And holodecks.
And the ultimate: time travel stories involving holodecks!
(Score: 1, Funny) by Anonymous Coward on Wednesday April 27 2022, @02:48AM (2 children)
true ultimate: time travel stories invlving holodecks, that were all in a dream sequence.
(Score: 2) by maxwell demon on Wednesday April 27 2022, @02:23PM
Holodecks dreaming of time travel!
The Tao of math: The numbers you can count are not the real numbers.
(Score: 0) by Anonymous Coward on Wednesday April 27 2022, @02:50PM
Enterprise FTW!!!
(Score: 3, Interesting) by acid andy on Tuesday April 26 2022, @07:53PM (1 child)
Also, the present might not exist or might have just ceased to exist, and we wouldn't know, because there's a lag between what our senses detect and what we perceive. We perceive the recent past.
https://en.wikipedia.org/wiki/Chronostasis [wikipedia.org]
Yeah, I know a lag in our perception and the ability of our brain to replay a past event isn't evidence for the physical existence of the past or non-existence of the present. I'm just muddying the waters for the sake of it. ;)
Master of the science of the art of the science of art.
(Score: 0) by Anonymous Coward on Wednesday April 27 2022, @02:55AM
or. the future is an intnded consequence, while the past is a regretful outcome we wish to have acted differently in the recent present.
(Score: 4, Interesting) by JoeMerchant on Tuesday April 26 2022, @08:15PM
We are all traveling into the future all the time. Relativistic time dilation can achieve forward time travel Rip Van Winkle style, take a 0.99C trip for a year, your time, come back to a world 100 years older (or similar - IDR the exact math offhand.)
We have limited time travel into the past, information only, limited bandwidth, but we can see and hear things as they occurred in the past through all kinds of recording and playback devices, including oral tradition storytelling.
Can we know with certainty things about the future? Predict the weather? Tomorrow's lotto numbers? Not with certainty, but some things can be accurately modeled and somewhat reliably predicted.
What's the next step beyond our current limited time travel abilities?
I can imagine the construction of a receiver which displays information that is not communicated to it until the future. At first this would likely just be a single bit with slightly better than 50% accuracy communicated "back in time" a few microseconds, but with development we might eventually be able to "FAX back" the front page of next year's New York Times, which should be enough information to significantly diverge the timeline... the timeline which received the page from the future would (in all probability) have a new front page on the New York Times declaring the day of the received page has arrived instead of the originally faxed back page, perhaps with an inset copy of the first received page answering the question: "were we just in a time loop, and if so how many iterations deep?" The originally communicated page would be different from the page created after its communication, but it would also contain information that could not have been known without the reverse-time causality events. Two distinct causality streams march forward from the point where the future information was received. I also expect that the energy requirements to communicate this information rise, dramatically, as the information becomes more reliable and extensive - it might require the energy equivalent of all the matter in Andromeda for that front-page back one year trick.
Україна досі не є частиною Росії Слава Україні🌻 https://news.stanford.edu/2023/02/17/will-russia-ukraine-war-end
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @08:08PM (13 children)
If time travel were possible, where are they? I mean, since Mr. Titor left.
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @08:19PM
we are happy-go-lucky caught in a burocratical rigidly enforced time-travel-free timeline.
(Score: 2) by Thexalon on Tuesday April 26 2022, @08:22PM (8 children)
Also: How did Hitler survive so many time traveler assassination attempts?
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 3, Funny) by maxwell demon on Tuesday April 26 2022, @08:43PM
https://www.tor.com/2011/08/31/wikihistory/ [tor.com]
The Tao of math: The numbers you can count are not the real numbers.
(Score: 4, Informative) by Freeman on Tuesday April 26 2022, @09:40PM (6 children)
Hitler was the least evil outcome? Seriously though, things could have been worse. Hitler did survive some assassination attempt too.
https://en.wikipedia.org/wiki/List_of_assassination_attempts_on_Adolf_Hitler [wikipedia.org]
I was going to count them, but then I found this entry:
So, I mean, he dodged quite the number of would be assassins. 22+ on that list, depending on how man you count that several as, could be 23 or 30 or I don't even know what to make of that.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by mhajicek on Wednesday April 27 2022, @01:56AM (5 children)
If Hitler had been assassinated, Germany likely would have won.
The spacelike surfaces of time foliations can have a cusp at the surface of discontinuity. - P. Hajicek
(Score: 4, Insightful) by Thexalon on Wednesday April 27 2022, @03:39AM (3 children)
I doubt it:
1. His most likely replacement, had the assassins succeeded, would have been Goebbels. Goebbels was in a lot of ways more detached from reality than Hitler, and had even less understanding of military matters and even less of a willingness to listen to military professionals.
2. By the time the assassination attempts really started coming on a regular basis, in 1943, Germany was already losing. Rommel was in the process of being kicked out of Africa. Göring and the Luftwaffe had utterly failed at the Battle of Britain, and failed to supply the 6th Army at Stalingrad, and the US and UK were bombing Germany and its captured territories on a regular basis. The U-boats weren't able to sink enough ships to keep supplies out of the UK. The US's and USSR's ability to build more equipment was really starting to make a difference and prevent German efforts from reducing the Allies' ability to fight. They were starting to face effective resistance in occupied territories behind the lines, especially in Yugoslavia.
3. Germany's allies were also starting to turn on them. Italy had lost so much in Africa that they were considering quitting. The Spanish nationalists were never really all that impressed and happy to sit on the sidelines. Romania and Bulgaria were angry because the German commanders had managed to lose their best army forces that they had contributed to the fight against the Soviets.
4. The giant strategic blunder that was Operation Barbarossa was going to happen no matter what, because Nazi ideology demanded it. As far as Nazi ideology concerned, they were going to win versus the USSR because their people were Slavs and thus in racist Nazi thinking were inferior to the Germans and thus guaranteed to lose. Reality demonstrated otherwise. They were also confused about why the Brits were fighting against them, since they thought of the Brits as Germanic cousins what with the Anglo-Saxons and Normans and such.
5. They never managed to sort out their massive supplies and logistics problems that had been a problem from the beginning. They didn't have enough stuff to win, and frequently no way to get it to where they needed it. There's a reason professional officers focus on those issues at least as much as tactics, but they aren't fun or glorious so screw it.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by Freeman on Thursday April 28 2022, @01:23PM (2 children)
By some definition of win, they were winning against the USSR. The issue is that the USSR didn't much care about their people and were just sending in so many troops. When I say troops, I mean cannon fodder. I.E. you get the magazine and the other guy gets the gun. So, when the other guy is killed, you take his gun and use the magazine.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by Freeman on Thursday April 28 2022, @01:25PM
Germany underestimated the USSR and they weren't prepared to fight a winter war.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by Thexalon on Thursday April 28 2022, @02:03PM
By the German's definition of winning in 1943 (the destruction of the USSR), they were losing. By the USSR's definition of winning (the successful defense of their government and most of their territory), they were winning. Killing more of the enemy than they kill of your guys does not mean you've won, as any Vietnam vet can tell you.
Also, the reason the Soviets had more stuff and more people in the right place to fight is that they had better logistics. They had methods that actually worked for getting things around the battle space, while the Germans were relying on trucks that kept getting stuck in the mud, planes that didn't even exist, and horses they couldn't feed.
The only thing that stops a bad guy with a compiler is a good guy with a compiler.
(Score: 2) by Freeman on Wednesday April 27 2022, @01:17PM
Depends on when he was Assassinated. A number of the Assassination attempts were undertaken by the Germans themselves when they saw they were going to lose the war.
Joshua 1:9 "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the Lord thy God is with thee"
(Score: 2) by EvilSS on Tuesday April 26 2022, @08:49PM
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @10:43PM
Time travel hasn't been invented yet, therefore there are no time travellers.
All possible worlds prior to the invention of time travel won't have time travel in them.
Unless we are living in a reality where someone explicitly has yet to travel here then we our possible reality hasn't forked from that of all time streams where time travel never existed.
i.e. Time travel never existed in 1955 when George McFly fell out of a tree. When Marty visited that forked the original time stream.
So from our perspective it's like time travel never existed because it doesn't yet, at least in this possible world.
(Score: 0) by Anonymous Coward on Wednesday April 27 2022, @02:14AM
That is one explanation for UFO sightings. Time tourists.
Or they are sneaking around and living it up.
Or we are in the pure timeline with no travelers showing up.
None of it sounds very likely.
(Score: 0) by Anonymous Coward on Tuesday April 26 2022, @10:01PM
I can think of one really, really stupid mistake that everybody will wish we could undo, but the Deplorable Word cannot be unspoken.
(Score: 3, Funny) by oumuamua on Wednesday April 27 2022, @01:00AM
And you'll be thankful you live in a universe where there is no time travel:
https://www.genolve.com/design/socialmedia/memes/time-travel-primer-2004 [genolve.com]
(Score: 1, Troll) by Mojibake Tengu on Wednesday April 27 2022, @11:48AM (1 child)
Why Quantum Mechanics and Relativity Theory must be logically supported by concept of of killing entities like boxed cats or grandfathers?
From the perspective of consciousness, that's insane. I say: a cultural error. Typical western narcissism.
If QM and Relativity are logically inconsistent without adding a concept of killing someone, they both are obviously mathematically wrong. They are built on inadequate primitive assumptions.
The concept of killing is nowhere to be found in Mathematics either, so it's undefined in any apparatus used as a model generator for any Physics.
The edge of 太玄 cannot be defined, for it is beyond every aspect of design
(Score: 2) by maxwell demon on Wednesday April 27 2022, @02:34PM
Never heard of a Killing vector? :-)
The Tao of math: The numbers you can count are not the real numbers.