# Time Travel

If time travel was ever invented, someone would have come back in time and we would have recognized them. If i ever invent time travel, i will return to this spot right now. *pause* I guess time travel will never be possible. Even if they invented some way of cloaking and forced people to use it, what are the odds that in our infinite future nobody will ever make it back in time without their cloaking? The knowledge would eventually spread to people who wanted it to be revealled in the past and we would know about it. Thus i conclude that time travel will never be possible.

Think in terms of a physicist. How would time travel be possible. Once you've found the answer to that question, so have you to your own.

You are confusing me now.

A) I didnt ask a question, i merely stated my logic.
B) Im not a physicist so i dont know how they think, maybe i should ask Moonbear to use his PhD in looking into other people's lives to help me.

Tide
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Even if time travel were off into the "infinite future" what are the odds of someone hitting this particular time and place - the Universe is very big and infinity is a very long time! :-)

Ivan Seeking
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Apparently Mallet feels these issues can be managed. He even thinks that he might begin receiving his own future signals as soon as the thing is started.

Edit: we are only talking signals in this case.

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What are the chances that you would land in a certain space in a certain time??? What is the use of time travel if its just a random movement, and you cant get back? You would think that even if the "random position" was highly unlikely to be in a certain spot, since the opportunity of time travel existing forever, someone would have randomly came back in time at every moment by now.

JasonRox
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You can't go back in time and create a time travelling machine in the past, and somehow by the time you back in the future, the time travel is old news.

That would violate the laws of nature.

Same as going back in time and killing your grandfather so you were "never" born. This action can not happen. You try and stab him, but for some reason the knife won't reach, or your hand is held back, or physics will cause you to never think of doing such action even if you wrote it on your palm.

I'm not a physicists, but I think at this point, I believe it's impossible. Saying it is possible is no different than saying impossible. People like to say it is impossible because that is "logical" thinking, but I don't think either is "logical".

Neither answer is a good one, so I stick to what I think.

Ivan Seeking
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I would think that a complete theory of time travel would address issues such as spacetime coordinates. The spacetimes points at which we would enter, or at least exit the machine, would have to be calculated; I guess.

musky ox, your example [about you traveling back to now] only shows that you won't do this. Also, by many accounts it appears that any real time machine would be limited to times within its own operational life. So, for example, you can only go back in time [in Mallets case, send a signal back in time] to the point when the machine was first turned on; but no further.

I believe my example shows that nobody can travel back in time passed the time when the machine is turned on then?

Ivan Seeking
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musky_ox said:
I believe my example shows that nobody can travel back in time passed the time when the machine is turned on then?

The fact the we know of no time travelers? I think this qualifies as logical evidence of such.

Just out of curiosity, how would we know one?

He would identify himself as one. He would bring something from the future, either some material or some information, that he could prove it with. If you think of an infinite amount of time for us, then surely someone againt cloaking time travel would eventually get back and time and be eager to reveal himself. They could never keep the secret of time travel hidden forever, so its only logical that someone would have travelled back in time by now. Thus time travel will either never exist, or never be able to come back to this time period.

Tide
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musky_ox said:
He would identify himself as one. He would bring something from the future, either some material or some information, that he could prove it with.

What could anyone possibly bring from the future that would PROVE he/she is/will be from the future?

Well, you would know things that would be going to happen in their future. If you could take back things with you, you could take back some advanced technology.

Ivan Seeking
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musky_ox said:
He would identify himself as one.

Haven't you ever heard of the Temporal Prime Directive?!!!

Tide
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musky_ox said:
Well, you would know things that would be going to happen in their future. If you could take back things with you, you could take back some advanced technology.

We have people telling us everyday what "will happen" in the future. Sometimes they are right. That doesn't make them time travelers. As far as advanced technology is concerned if it could be made in the future then it could be made in the present. There's no proof there.

Ivan Seeking
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The thing is, musky ox, what you argue might be true, but it wouldn't have to be. I can argue that any time traveler would remain hidden. From there we have an impasse.

But how would they be hidden? If it was some sort of cloaking, then surely someone in the infinite future would have made it back in time without the cloaking. Yes technology could still be made in our time, but if its something beyond where we are right now, then i think he would be able to prove himself. For example... if someone went back in the past from now to 500 years ago with a computer, im sure they wouldnt doubt that he was from the future.

HallsofIvy
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"Hidden"- going back to a time or place when no one would recognize them and not telling people who they were! NOT taking a computer (or transistor radio, or wristwatch, etc.) to times when those had not yet been invented!

Surely it's not that hard to grasp that someone COULD do those things and so your argument against time travel is invalid.

Well, whether or not our existance is infinite, im not sure. However, if we assume that it is, then eventually someone who WANTS to reveal the ability of time travel to the past will do it. Even if they tried to keep it secret, enforce rules, etc.

Its a whole different story if you say that time travellers are invisible (non-existant) to us. However, what would be the POINT of travelling back in time if you were just a spectator?

I'm not saying you can't slow down a photon or an elemetary particle using laser that would relatively be a "time maching". I'm saying how would you travel back into time according to today's current theories.

Gokul43201
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musky_ox said:
If time travel was ever invented, someone would have come back in time and we would have recognized them. If i ever invent time travel, i will return to this spot right now. *pause* I guess time travel will never be possible. Even if they invented some way of cloaking and forced people to use it, what are the odds that in our infinite future nobody will ever make it back in time without their cloaking? The knowledge would eventually spread to people who wanted it to be revealled in the past and we would know about it. Thus i conclude that time travel will never be possible.

Maybe time travel is invented in say, 2050. After a few inital tests, it is declred illegal and carefully controlled. It is theoretically possible but no one gets to use it. So you'll never see them.

Or perhaps, only some limited form of time travel is allowed/possible. You can't (legally/physically) go back more than 1 month into the past.

Even if time travel were unregulated and assumed to occur freely in the future, you have to demonstrate that the probability of your worldline not belonging in the range of say, a one-on-one map from the domain of all worldlines of people in the future to the co-domains of the wordlines they visit in their past, is small (compared to 1). How's your Cantorian Set Theory ?