What sort of technological developments could be used to this effect?
There are some concepts on some limited forms of time travel based on utilizing extreme objects that may not exist (like cosmic strings) or forms of matter/energy that may not exist (“negative” energy). But there is absolutely nothing to suggest any possibility of time travel like in science fiction. A very large part of science fiction is fantasy magic presented with a different name.
A recent article.
It’s theoretically possible to travel into the future. We just need to solve the whole accelerating to near the speed of light safely part. I doubt we’ll ever get there in practice, but at least it’s theoretically possible.
Entropy can only increase. Time travel to the past would require an earlier state of entropy, which is impossible.
Time is a property of space. They are not two separate things but one combined thing that we do not understand. And entropy is a feature of space/time and cannot be reversed.
Travel into the future does not violate entropy, so it may be possible. Time travel into the past will always remain impossible.
Also see the short story of the same title by Larry Niven as a counterargument.
Technically speaking, we are all traveling into the future; traveling at relativistic speeds relative to a particular reference frames compresses the subjective duration it takes to progress with respect to that frame.
That isn’t a valid argument with respect to movement against space-time; entropy is the development of the thermodynamic state within a reference frame. In fact there are multiple ways within the theoretical framework of General Relativity to travel ‘backward’ in time, although whether it is actually possible to realize these is another question.
Stranger
Travel into which future?
Back in the 70s, perhaps when we were kids as I was then, we might have seen “Space 1999” as being somewhat prophetic. However, there’s no way it could have been really as it is now 2024 and we still don’t seem any closer to achieving interplanetary space travel. However, as far as technology here on Earth goes there has certainly been a great deal of development. You have to ask yourself, how many people had VCR’s, mobile phones (or indeed landlines for that matter) or computers back then?
How do we know the technology we’ve got now isn’t gradually and inadvertently leading up to the discovery of time travel? It allows us to store data for future use. How do we know that, at some Earth’s future, we won’t be able to store points in time and space so that they can be recreated as the “present” we are currently existing in? Also, how do we know there aren’t parallel universes we may be able to travel into one day where our past, or future, is their present?
There’s actually a scientist called Ronald Mallet who isn’t as sceptical about time travel becoming a reality as the rest of us:
The former Doctor Who actor Tom Baker narrated a documentary on his work which can be found on YouTube.
The Wiki article also points out the problems with his time travel theories that have been pointed out by other scientists and even himself. Ronald Mallett - Wikipedia
Theoretically? You’re doing it right now!
I guess “time travel” in a popular sense means that a human can travel to the future or the past. I will now explain one reason why this is not feasible. Maybe it is possible for a single particle to travel forward in time faster than the “natural” speed of time (however we define that for the purpose of this thought experiment) or backwards in time, though I don’t see how the backwards part could work without FTL technology. But for all practical purposes, we are asking about us traveling, right? And that is not possible because there is no absolute spacial frame or reference ( → realtivity). In fact, there is not a temporal frame of reference either, but that only makes it worse, so I will not even consider that now. Let me elucidate:
We are on the surface of a planet that is travelling really fast through space. How fast? That depends on what we measure the speed against. We could measure it relative to the Sun, or to the centre of the galaxy, or whatever. All those measurements are arbitrary, as there is no absolute set of valid coordinates.
Now for the sake of reductio ad absurdum imagine we could travel in time. Let us go back, just one day. Where would we land? If we land where Earth is “now”, we are in the vacuum of space: we die. We not only have to travel backwards, we have to move. A lot. But how much? We have to land on the surface of the Earth, there is no way around that. A couple of meters too deep, and we are dead and buried. A couple of meters too high, and we are floating in the the air. For a short while at least, then we fall and crash and die. We have to get it right to a centimeter, better still, under a millimeter. But we can not choose any frame of reference. Because there isn’t. So time travel, as much as I regret it, cannot be achieved.
Time travel (in any direction) is trivially easy once you get yourself into a supermassive black hole. You can flit about between past and future as much as you like, but with just two restrictions. You can never come out of it, and you’re inexorably and fatally drawn into the singularity, because that’s your new timeline.
But still, it’s time travel.
True for some definitions of the t coordinate… but then, if we’re going that route, we could just define the t coordinate in a way that lets us do that outside of a black hole, too. Or we could define “time” in a more systematic and consistent way, in which case the definition inside the black hole has the direction towards the singularity being the time direction.
High speed travel towards an object will age it in your reference frame. Thought the amount of extra age is equal to the time you save traveling relativistically to it.
The last three plus the one where…n/m.
This was a plot point in a Superman story a long time ago. Supes was under some sort of spell where he couldn’t leave the Earth but he really needed to, to defeat the bad guys.
So he time travelled back in time a day, and < hand-waving > didn’t do the normal adjustment that he did on all previous time-travelling where he moved to keep up with the Earth, oh yeah, didn’t Supes ever mention that adjustment before?</ hand-waving > and so he didn’t leave the Earth, the Earth left him by moving forward in its orbit, so he complied with the spell and went after the bad guys.
Indeed! I am now 5 hours into your own future! < head explodes >
Since this is speculation and opinion more than just sharing, let’s move this to IMHO (from MPSIMS).
In threads like these, I always introduce Kip Thorne’s ‘temporally-displaced wormholes’ method. Kip Thorne is the bloke who advised on the movies Contact and Interstellar.
That is the only method I’ve ever seen that would work reliably, and can guarantee that you don’t get lost in time and space. (If only you can manufacture wormholes in the first place).
1/ build a wormhole, with two connected mouths maybe ten metres apart. You can walk through the wormholes and pass from one mouth to the other without passing through the space in between.
2/ send one wormhole mouth off on a relativistic spaceship, travelling a circular path several light months or lightyears long. Time dilation will cause the two wormholes to be temporally displaced from one another. The amount of displacement depends on how fast and how far the spacecraft travelled.
3/ place the two wormholes back on Earth and walk through them in either direction. If you walk in one direction you go to the future; if you go the other way you go to the past. If you want to travel into the far future you can just keep waling through the 'hole in the same direction over and over again till you get to when you want to be.
This method of time travel would get round Pardel-Lux 's problem of rematerialising inside the Earth or in outer space; the two mouths of the wormhole would be both safely on Earth, and you couldn’t go anywhere else. You could, however, go elsewhen.
There are ways of proving the impossibility of time travel backwards. Paradox ensues. Causality gets messed with. But I think we take this impossibility at our peril.
For one thing, I recently read an article in Scientific American describing proof that the universe can’t possibly be both “local” and “real”. In this context, “local” means that when events have causes, the causes have to occur where the event happens, which includes for example some kind of radiation or information traveling from elsewhere and reaching the location of the resulting event. And “real” means that objects exist regardless of whether we observe them, i.e. the Moon is still there now even if nobody happens to be looking at this moment. I find it obvious the universe is both local and real, but they say this can’t be the case. So, bizarre impossibilities may exist.
For another thing, our understanding of existence changes so rapidly. I remember my grandfather, his humor, all the neat things he worked on, his kindly and indulgent and soft spoken ways, and his black Pontiac automobile with all the dark brown cloth interior. He was an inquisitive and bright 7 year old when the electron was discovered, and a teen when special relativity was introduced. Things looked a lot different then, and it wasn’t so long ago, just a century and change. We can’t imagine how different things will look after another century, let alone a thousand years, or a million – and in the grand scheme of things, what’s a mere million years? The briefest of flashes, hardly detectable.
Things that can be proven today could look like anything in only a little while…