Does this prove time travel is truly impossible?

[D.B. Cooper]

My friend said that time travel will always be impossible because we haven't been visited by anyone 10 years, 100 years, 1000 years, 1000000, a billion, a trillion years in the future.

[Tankfriend]

How do you know? Perhaps they have just chosen not to reveal themselves?
Or they developed a "real" stealth system in the future so they are invisible...

I guess the possibilities are almost endless if you are talking about time travel, because we today don't know anything about the full potential that technology and science could reach in the future.

[General A. Skywalker]

How do you know? Perhaps they have just chosen not to reveal themselves?
Or they developed a "real" stealth system in the future so they are invisible...

Exactly. Maybe there are some guys from the future amongst us, but they try not to attract attention. Maybe I am one of them, who knows??!!

[Axeman]

I am sure Time Travel is impossible, but hypothetically lets say it isn't. I am sure we would have the common sense to make sure that we didn't change history at all, so I could forsee an "observer" as in an unseeable, unhearable, untouchable, unsmellable person from the future observing or something, but I doubt it.

[the_mango55]

I am sure Time Travel is impossible, but hypothetically lets say it isn't. I am sure we would have the common sense to make sure that we didn't change history at all, so I could forsee an "observer" as in an unseeable, unhearable, untouchable, unsmellable person from the future observing or something, but I doubt it.

I think a more realistic way of observing the past (provided FTL is possible) would be to send an unbelievably powerful camera to a point in space just before the light from some historical event is going reach it (you would probably have to move it over a bit too so it wouldn't record itself flying into position), then record that event, and FTL travel back to earth.

Exactly. Maybe there are some guys from the future amongst us, but they try not to attract attention. Maybe I am one of them, who knows??!!

Them goobacks terk ar jyerrbs!

[Simetrical]

You cannot travel back in time, surely. Travelling back in time means that your matter would have to be duplicated. If you built a spaceship and went back in time, then your spaceship would exist twice, once as the one you're in, and the other as a ship being launched by you.
And that is nonsense.

Why? No reason it's impossible.

To start going back into time, I guess parallel universes would have to start being used.

Parallel universes would not be relevant to a wormhole-based time-travel method.

Travel forwards is far more likely, as it is technically possible to determine exactly what would happen in a certain amount of time from any position (though would require vastly more knowledge and computing power then we have now)

Not true. It's not possible even in principle, given quantum mechanical randomness. Even without that, you'd have to get literally infinite precision to be able to predict things into the indefinite future, due to chaotic systems, and that seems impractical even classically. Furthermore there are information-theoretical limits on how much computing power is available in the universe (although that steps back into quantum mechanics again).

[Ky Colonel (not of KFC)]

But if you used that wormhole to go back in time and killed your grandfather, then parallel universes would have to be used. Since your lineage obviously didn't stop with your grandfather.

I wish there was a better theory than this one. Anybody got any competing ones? I call lack of free will.

[Tankfriend]

Hmm, isn't that the so-called "grandfather paradox" or something?

-> "normal" timeline

-> you get a reason for killing your grandfather (this would be the "start" of the whole complex)

-> travel back in time, kill grandfather

1st possibility:
-> grandfather has fathered your father already (what a sentence )

-> you yourself probably still exist, but you possibly kill your grandfather before he has provided you with the reason to kill him, effectively removing the reason for which you decided to kill him in the first place

-> no reason to kill him, no reason for time travel and therefore you never decided to kill your grandfather; loop back to the start

2nd possibility:
-> you kill your grandfather before he has fathered your father

-> you yourself cannot exist (as your father never existed)

-> you cannot have killed your grandfather at all; loop back to start

The important thing here is that that would only work without parallel universes and therefore creating a time paradox. With parallel universes included, there would not be a paradox (but what would happen then?). I guess the question would have to be: Are there parallel universes?
Btw, that's constructed from the wikipedia articles I have read as well as some thoughts of my own, I'm not a scientist in this area...

[The Count(er)]

I am sure Time Travel is impossible, but hypothetically lets say it isn't. I am sure we would have the common sense to make sure that we didn't change history at all, so I could forsee an "observer" as in an unseeable, unhearable, untouchable, unsmellable person from the future observing or something, but I doubt it.

it's not really possible to change history because if you did change it you would of already changed 1000 years ago or whatever and before going back in time wouldn't even know you did it in which doing what ever you want back in time would have no consequence when you get back because you already did it meaning for example if you were to try to kill some historical figure before his time you would of already failed because history books will still say he died at his normal time

[Gary88]

no, one of the caveats of possible ways of travelling through time would be that you would not be able to go back earlier than the method was devised. so if it hasn't been invented in the past its no wonder we don't have crazy future people here.

[General A. Skywalker]

no, one of the caveats of possible ways of travelling through time would be that you would not be able to go back earlier than the method was devised.

Why not? Because there has to exist some kind of "entrance" (sth like a port or machine)?

[Gary88]

you'll have to ask someone else because its not something i've ever paid attention to. basically there are ways that theoretically you could travel in time relatively just not back before you started. for instance say you travlled close to the speed of light and so aged slower than everyone on earth (you're naturally in a space ship) you could come back to earth after what to you seemed like 5 years but you're actually 200 years in the future (the numbers are just made up of course) but you couldn't turn up before you left

[Tankfriend]

Well, I guess there is nothing possible other than speculation concerning the topic of time travel.
I mean, everything that science has come to are mere theories, and as everyone knows, theories can be correct, but are not necessarily so.

Anyway, time travel into the past would be kind of "cool" for certain things (historical research anyone? ) but of course it would also present a lot of possibilities for ******* things up completely should there be a possibility to influence the past.

[Simetrical]

This doesn't "prove" that time travel is impossible. It can be taken as evidence that it's not as likely to be possible, but even that isn't really solid. As Gary88 alludes to, one relatively likely-seeming possibility (travel through a wormhole) won't allow travel to before the wormhole is created. Of course, if it's an old wormhole, not custom-built for time travel, that might not be an issue.

[Pra]

This doesn't "prove" that time travel is impossible. It can be taken as evidence that it's not as likely to be possible, but even that isn't really solid. As Gary88 alludes to, one relatively likely-seeming possibility (travel through a wormhole) won't allow travel to before the wormhole is created. Of course, if it's an old wormhole, not custom-built for time travel, that might not be an issue.

Doesn't the idea of a wormhole violate the theory of thermodynamics?

[andrew.murphy1]

Worm-holes are the most likely answer physicists have today, and worm-holes do allow time travel to the past and future. The main problem with that theory, however, is how to negate the effects of the ridiculous amounts of radiation that you produce when you create a wormhole? until someone learns how to overcome extremely high doses of radiation, this won't be happening, unfortunately :/

Finding yourself another 'pre-made' wormhole would also have serious drawbacks: 1) we dont know of any, 2) they could be at an effectively infinite distance from us, 3) they almost certainly don't lead where you particularly want to go

anybody wondering about the possibility of white holes as a method of travel, maybe not through time, but certainly through space...???
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Tankfriend:
but of course it would also present a lot of possibilities for ******* things up completely should there be a possibility to influence the past
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How do you know you aren't just influencing another parallel universe, and therefore travelling back in time, wondering around and then coming back won't change the present?
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Simetrical/ Gary 88:
As Gary88 alludes to, one relatively likely-seeming possibility (travel through a wormhole) won't allow travel to before the wormhole is created.
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What stops you from creating the wormhole in the past from the present? If what you two say is true, then it is thereotically possible to create a wormhole with one entrance and no exits??? =S .... Again, it could just be a parallel universe (what we perceive as the past), in which case you can make the exit of the wormhole just as easily as the entrance.

[Tankfriend]

How do you know you aren't just influencing another parallel universe, and therefore travelling back in time, wondering around and then coming back won't change the present?

How do you know if the universe you could perhaps change and *think* to be a parallel one is not our own future one in the first place?
But enough of this, that could go on and on for all eternity...
I think I'm just going to travel to the past and provide you with the idea in the quote above so we get locked up in a causality paradox...

[chriscase]

Ronald Mallett has a working theory and design for a time travel machine. But similar constraints apply to the theoretical operation of this machine: it can't send anything back in time to before it starts running.

[andrew.murphy1]

Tank Friend:
How do you know if the universe you could perhaps change and *think* to be a parallel one is not our own future one in the first place? :wink:
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That's a very fair point, and like you said:
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Tank Friend:
But enough of this, that could go on and on for all eternity...
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There are too many things it could be

Chriscase, I thought that Mallett's initial ideas weren't going to work? and he admitted that he was working in the wrong direction in trying to slow down light ... if memory serves, I think his idea was to get a ring of lasers, and bend light to warp or loop space-time fabric. The theory goes that to manage this he only had to:
a) do this in a vacuum and b) lower the speed of light.
And physics tells us you can't do both of those at once:
if you do the experiment in a vacuum, the speed of light in free space (c) is obviously still the same...
Or using Snell's law, you can lower the speed of light by passing it through a medium, but then the experiment isn't being done in a vacuum

it was an interesting theory while it stood up though.
anybody else know of any viable method of time travel???

[Simetrical]

Worm-holes are the most likely answer physicists have today, and worm-holes do allow time travel to the past and future. The main problem with that theory, however, is how to negate the effects of the ridiculous amounts of radiation that you produce when you create a wormhole? until someone learns how to overcome extremely high doses of radiation, this won't be happening, unfortunately :/

The bigger problem with the theory is that nobody has any idea if the solutions of the field equations that permit wormholes are actually physically meaningful. Nobody knows whether wormholes are possible in the first place.

What stops you from creating the wormhole in the past from the present?

I don't think it makes any sense to speak of "creating something in the past": if it's in the past, it already occurred before you created it. In principle, space-time contains time and does not change with respect to it. You can't have a point in space-time that contains no wormhole at one point in time, and then does contain one at another, because then it will no longer be at the same point in space-time, by definition. If part of the wormhole is created in the past, it will need to be by something within that point's backward-pointing light cone, which does not include any future point.

But I don't know much about this kind of thing.

If what you two say is true, then it is thereotically possible to create a wormhole with one entrance and no exits??? =S .... Again, it could just be a parallel universe (what we perceive as the past), in which case you can make the exit of the wormhole just as easily as the entrance.

A wormhole is just a portion of space-time whose interior is not simply connected. Any entrance, presumably, is also an exit ― or at least if it's not, it's not because of something intrinsic to the wormhole, I don't think. So I don't think the distinction you draw is a meaningful one.