Should time travel be done? (Speculation)

If someone would actually discover method of time traveling, do you think it should actually be allowed? Time travel is pretty dangerous after all. I mean, nobody knows how it would actually work in real life so only real way to find out would be to test it, right?

Even small things could cause in Butterfly of Doom thing, I mean, if you go back in time to meet your parents before you were conceived, even if you don't tell your identity or alter anything, you might somehow prevent your own birth. I mean, each human is born from particular sperm and ovum, if you manage to alter time your parents conceive you, say by week, then you won't ever have born because it was different sperm that conceived you. Heck, for all we know, even having physically existed in past(as that would already have changed past by having you exist in it even if for temporarily) might cause butterfly effect.

Even if you don't travel far back in time/to future(like, only few hours or minutes), you don't know what even minor paradox could cause. I dunno if it would actually cause something bad to happen, but do you think it would really be worth to find out?

Note that if you are one of people who thinks time travel would be great to find out truth about history and stuff, it would be better to figure out way to see in past instead of physically traveling back in time.

I think this all depends on which Time Travel Tropes turn out to be correct. If You Already Changed the Past is in effect, we're safe.

@Spooky Mask: Is time travel even possible?

Well, that's the thing. For the last twenty years, theoretical physicists have been looking for a law that makes time travel impossible. They have yet to find one.

@Morwen: Well, this thread assumes it is possible, after all it is speculation thread. And Einstein apparently made theory that says its possible and they haven't been able to deprove it yet, so...*shrugs* Anyway, even if it is physically possible, its different thing whether it can be done in practice. But this thread isn't about that, its about whether it should be done if someone would discover how to do it.

The most practical method of creating a time machine involves making a wormhole, and then temporally displacing one end through relativistic time dilation. If such a time portal were created, I imagine both ends would be heavily guarded.

It's not like the technology would easily fall into the wrong hands, given the prohibitive time and expense it would require.

Well, if it's possible then IMO I think it should be done under controlled conditions. There's the obvious "no interference with the past." But then there's also "use a pseudonym if you have to introduce yourself."

Also, "Bring a translator if you are going to a country where your language isn't the dominant one and you have no idea how to speak it."

Spooky Mask, what's your first language, since you mentioned before that it isn't English?

edited 22nd Aug '12 3:47:44 AM by MorwenEdhelwen

Finnish And I do actually have good grade in subject, its just that grammar isn't automated for me.

Even if its safely guarded, wouldn't it still be very dangerous since you don't know how it will affect reality?

I'm not really expert on subject and next example might not make any sense to anyone, especially since I'm not best at explaining, even in Finnish, but... Say, you play game coin toss game on computer where chance should be evenly 50/50. You get tails. Then you time travel back in time when you are playing the game before game had decided which side wins. Wouldn't it be possible that it lands on heads this time as by traveling back in time, you already altered the past merely by existing in it? This probably wouldn't make sense to anyone since most people(including I) would just assume that it gives same answer this time too.

Well, in quantum mechanics, once a eigenvalue is observed the wavefunction collapses into that state, so subsequent observations yield the same result. The question is whether someone observing it, and then going back in time to before the measurement took place will count as a prior observer or not. I'm inclined to say no.

On the other hand, it depends whether the person was already there the first time, given that if they were, the initial conditions are identical, and thus the outcome should likewise be the same. If they were not then their trip into the past has led them into an alternate reality, in which case all bets are off.

edited 22nd Aug '12 4:08:57 AM by Elfive

The only way for it to be consistent with Relativity is You Already Changed the Past, since GR only has the one spacetime, and discontinuities in that spacetime would be really bad. I have no idea about QM, though.

QM generally obeys relativity. For example, even in quantum teleportation information cannot move faster than the speed of light, because you have to transmit what is effectively a "decoder function" by conventional means for it to work.

Honestly I'm not sure if it should be done. I believe the prevailing laws of physic's state that any "changes" you make would have already happened otherwise you would have never been able to go back in the first place. However, what if we turn out to be wrong and a paradox forms? How exactly do you conduct a non-lethal experiment for an event that could rewrite reality?

I'd just like to note that so far I believe only time travel into the future is proven to be possible (just insanely hard to do) so I think the worries about changing the past are moot.

Unless time is cyclic, in which case travelling far enough in the future will get you into the past.*

edited 22nd Aug '12 7:26:40 AM by Elfive

Certain theoretical machines do allow you to travel into the past, but only as far as the machine was constructed.

@Kostya: Thats pretty much what I was wondering...

Its kind of interesting though, if someone in future had invented time traveling to past, they either never went far enough to past that anyone would have noticed, left no trace of themselves or simply never used their invention. Though I suppose if time traveling to past is impossible according to physics, that also explains why nobody has done it

Thats also something that I wonder... If anyone figures out how to do time traveling, would we test it or would we actually not do it in case it turns out to be dangerous? I mean, its not like it would be first dangerous thing we have tested out...

edited 22nd Aug '12 7:36:31 AM by SpookyMask

They might start by sending information.

Maybe that's what precognition is. Someone beaming information into people's heads from the future.

For all we know there are traces of them it's just incredibly hard to find them since the Earth is so huge and there are so many people. It would have been a lot easier centuries ago since a random person could just show up in town and say they were from another place. There weren't exactly any birth certificates to prove them wrong.

I'm sure someone would test it out of simple curiosity. However if we assume "you already changed the past" is true then we wouldn't even realize.

Scary thought...

I know at least one person says alien abductions are actually humans in the future trying to preserve their genetic stock or something. I don't think that's taken very seriously though.

I'm curious, do the laws of physics state that tricked out time is impossible? Technically you are changing the past but nobody would notice so it's probably debatable what effect it would have.

It's worth noting that Einstein did not say time travel was possible — time travel into the past, anyway. We travel into the future continually and can accelerate that process via relativity, but that's not what's being discussed here.

Einstein's equations of relativity demonstrated that Faster-Than-Light Travel, of any kind — warp drive, wormhole, portal network, whatever — would allow information to travel backwards in time from the standpoint of causality. However, no mechanism for achieving FTL travel is actually predicted by this. Moreover, as was stated earlier, it is impossible (within Einstein's framework, anyway), to go back to a time earlier then when you left, from your own point of view. So traveling to your own past is impossible.

A famous maxim in science fiction goes like this: "Causality, relativity, FTL Travel; pick two."

A multiple-universe theory is not predicted by relativity. Quantum physics and superstring theory do allow for the possibility, but it's generally accepted that any mechanism that actually let you travel to and change the past would create (or occur in, the semantics are tricky) an alternate reality.

"Changing the past" is kinda nonsense, logic-wise. The whole concept of "change" implies you have an axis of time to compare the "before" and "after" versions of something.

Since the time axis is included in the subject of observation, then there is no "change"; just a static, self-consistent-but-possibly-headache-inducing 4D block of events, or else time is in fact 2-dimensional. In which case we all start arguing about what happens if you then build a metatime machine.

That idea was already explored by Robert A. Heinlein in The Number Of The Beast.

Purely observational time travel into the past (ignoring the logistics issues of 'you can only go back until the machine was created'—let's say it happens through a wormhole) would be absolutely amazing and invaluable for history. It's ridiculous how much we could learn if we just got to, for instance, get a recording of a scribe and a vizier in ancient Egypt arguing with each other, if we had a chance to take pictures of all of the books in the Library of Alexandria, and so on. The implications for our understanding of the past would be absolutely massive, without even having to interact with the world.

It would also make it impossible for anyone to hide anything. I mean, it would allow you to spy on governments without them being able to do anything unless it has limitations.

You could also take it to Jerusalem, point it at a certain hill, set the timer to 2000 years ago or thereabouts, and solve one of the biggest arguments of all time.

Or start a humongous international incident.

edited 22nd Aug '12 9:23:32 AM by Elfive

Observation-only time travel would be incredible. However, quantum mechanics states that observation affects the thing being observed; there's no way to be "present" in such a place without altering it in some way, no matter how minute. For example, if you had some form of physical recording device, it would displace air. Regardless of the physicality of your recording method, you couldn't see anything without affecting the motion and energy state of photons; nor could you hear anything without affecting the motion and energy of the air.

In short, observing the past in "read-only" mode is impossible unless something was already there in the past doing the recording. So either You Already Changed the Past, or you change it by observing it. There is no alternative, unless you're using magic.

The next best thing is to observe the past while changing it as little as possible. Perhaps by using a very small recording device, that looks like a bug or something.