The Time Travel Discussion Thread

[Narz]

Do you believe time travel will ever be possible for humans?

If so, how the heck would it work?

Would it be possible only to travel forward? If you traveled back, what would happen to your future time? Would two separate realities form? If so, could you ever go back to your original present or would you be stuck in the new bifurcation you created by going back?

And of course the weird situation of having TWO yous (if you went back to when you were 8 or 16 or whenever you wouldn't turn into your former self, you would be there WITH your former self). Wouldn't this break the law of "matter cannot be created or destroyed), after all the, new matter could constantly be pumped backwards, creating a new reality (or multiple new realities) with way more matter than it would otherwise have.

Do any serious scientists actually concern themselves w/ these questions?

The idea of thinking about it I just find fascinating. Basically because I know so much more now than I did then. Also, cause I've lost or lost touch w/ so many people over the years. Also, cause it would just be cool to experience.

I doubt it will be possible in my lifetime (perhaps not ever, especially if society cannot handle the challenges of the next century or two), but it's fun to think about.

Anyway, this thread is to talk about time travel in a scientific (as well as a "it would be cool if") manner.

 

[The Yankee]

We travel forward all the time.

But, given that there have been small differences in atomic clocks between one on the ground and one on a spacecraft would show that it is possible to "travel" to the future, albeit, for any noticeable effect, it would take technology greater than our own.

I don't believe it's really possible to travel backwards and the possibilities arising from going back there (which you mentioned) give me a severe brain cramp.

I also had a thought that since we can see the past merely by watching the light hitting us now from distant places, that one could "travel" back if only you could move faster than that light. But then again, just because you can move faster than the images can doesn't mean that the matter will be where it used to be. And then I got another brain cramp.

Such things are for minds far greater than my feeble own.

 

[brennan]

Theoretical ftl particles have time reversed world lines. If you look at a Feynmen diagram of creation of a particle/antiparticle pair that annihilate shortly after, you can look at it also as a single particle that travels forward in time and then backward in time along a slightly differnet path.

Given how hard it is to move through time at a slightly reduced rate (relativistic velocity needed) how hard would it be to move from one point in time to another without passing through all the moments inbetween? We can't teleport in space yet.

 

[warpus]

I think the only way for you to travel backwards through time would involve you setting up an entrance to a wormhole.. anchoring it in a specific place in time.. and then holding on to the other end for a couple hundred/thousand years (or however long you wanted to), which would allow you to travel back to the time when you first created the wormhole.

Of course this would require amazing amounts of energy.. and a very advanced understanding of physics.

but I don't think it'd be possible to just travel to wherever you wanted to, as it is often portrayed in movies.

 

[xienwolf]

Actually I have thought quite a bit about time travel, and I think that it would indeed be possible, but that our present views on the subject are rather romanticised compared to the true possibility.

First step is: Why does everyone discuss time travel before scrying? Scrying would be SEEING through time, and personally I like to have a windshield on my car before I go 60 mph down the highway...

Really, one must start with being able to see where they are going, otherwise you run into massive complications. Hence the first possibility which must be worked toward is scrying, not time travel.

As for time travel, I do not think that all of those paradox dilema are even valid problems. You are just adding another direction to your options for travel, and as such, you can still only travel to a place (well, now place/time) that exists. Hence, you will only encounter the same objects in the new time you move to if those objects happen to be 4-dimensional entities which also extend in the same direction as your travel.


The standard method for thinking about 4-dimensional travel is to consider a being who can only see 2 dimensions suddenly gaining a 3rd dimension of travel.

So, let's say that there are beings living on page 26 of a book, and that the pages of this book when closed have no gaps between them. One of these beings discovers how to travel in the third dimension without being able to see in the third dimension and decides to try the "Down" setting first. He meets quickly with Page 24 in a catastrophic colision and is dead without ever managing to leave Page 26.

Now, if the book happens to be open to Page 26, and he happens to have learned how to look in the 3rd dimension, or just randomly selects to move "Up" first, he manages to break free into the 3rd dimension.

To parallel time more appropriately, let us assume that the book is falling. This allows it to travel in the third dimension, but always in 1 direction. Having just moved himself off of the page, our Flatlander now finds himself floating suspended above the book. There is nobody and nothing there with him. He sees just empty space.

Of course, if someone were reading this open book while it was falling, and they had their finger on the page to indicate where they were at, then he would view a strange circle moving left to right, then disappearing only to appear at the left, but slightly further from him, and travel again to the right.


So, bringing it back to Time travel. Assume that the world happens to be a 4-Dimensional object, and that you manage to move to a new 4th dimensional co-ordinate that is still near the world (but safe to move onto). You now find yourself on the earth, but unless people are ALSO 4-dimensional objects, there will not be any people. Well, unless there is a completely seperate set of people existing on the earth at a slight 4-Dimensional displacement from ourselves that is.

Were the world not a 4-dimensional object, then there is really no telling what you would manage to find around yourself when you suddenly shift yourself in the 4th dimension slightly.


Since people are constantly traveling forward in time, it would be like if you were with a line of people holding hands and walking across a field. Let's say that every couple of steps you move 1 person down the line to the left while everyone else maintains their same position in the line.

Now, you wanted to go back and see that person you were standing next to 12 steps ago, so you discover the ability to walk backwards. You figure that walking backwards 12 steps will put you back in contact, and so you begin your travel.

Problem is, you just left the line, which is still traveling forward. And nobody was following the line. So when you move back 12 steps and again begin walking forward, you find yourself covering familiar ground (which exists in that expanse of the 3rd dimension), but you are now alone (because your line of people do not exist that far into the third dimension).

 

[Eran of Arcadia]

I alwasy assumed that if travel back in time were possible, they would have gone back from when it was invented to now and told us.

 

[Masquerouge]

So my question is, if time travel was possible, why haven't we seen anybody from the future yet?
Possibilities are:
a. time travel is widespread in the future but you can only time-travel to another "reality", not your own. (whatever that means)
b. time-travel is possible but so difficult that very few travels by very few people occur, and using them to visit us does not make sense
c. time travel is widespread but people for some reason decided to not visit us, which could be slightly insulting or very wise.

Also, is FTL travel related to time-travel?

 

[Eran of Arcadia]

C doesn't seem likely; I mean, look at all the threads here where they ask what time period you would visit if you had a tank or a machine gun or something, and how many people responded that they would try to take over the world with them, and then tell me that idea will never occur to anyone in the future.

 

[Masquerouge]

C doesn't seem likely; I mean, look at all the threads here where they ask what time period you would visit if you had a tank or a machine gun or something, and how many people responded that they would try to take over the world with them, and then tell me that idea will never occur to anyone in the future.

I totally agree. So we can probably rule out the "time travel becomes a widespread technology that anyone can use to travel back to their own reality".

 

[Mirc]

My general opinion on this is like this and I've heard nothing but semantics games as arguments against my views:

Time travel is not possible. This means you cannot travel TO OUR OWN PAST. Traveling in another dimension in a different time there, somewhere where the past has been identical, assuming it would be possible, is STILL NOT TIME TRAVEL. It's an imitation of time travel. It's like saying you can draw a beautiful black and white painting while in fact you are only able to photocopy a great one. Yes, the end result looks the same, but it's not the same thing. Lastly, I believe traveling to other dimensions and things like that are not possible either with our understanding of physics (would break quite a few basic laws of physics, but those will anyway change as our understanding of physics gets greater).

Thus, my personal conclusion is that it can never be proved to be impossible, but it's as possible and likely as discovering a new continent where there is no friction and inertia.

 

[warpus]

Or maybe you can simply observe the past, not actually go there.

 

[brennan]

I've never heard anything that suggests to me that Time Travel might ever become a reality.

 

[Mirc]

Or maybe you can simply observe the past, not actually go there.

True. That seems perfectly possible, and it doesn't need any total revolution of physics either.

 

[Erik Mesoy]

So my question is, if time travel was possible, why haven't we seen anybody from the future yet?
Possibilities are:
a. time travel is widespread in the future but you can only time-travel to another "reality", not your own. (whatever that means)
b. time-travel is possible but so difficult that very few travels by very few people occur, and using them to visit us does not make sense
c. time travel is widespread but people for some reason decided to not visit us, which could be slightly insulting or very wise.

Also, is FTL travel related to time-travel?

FTL travel is certainly related to time-travel.

As for the possibilities, here's another:
d. time travel requires opening a "door" at either end and so one can't travel back to a time earlier than when (and where) the first "door" is opened.

Current physics, as I understand it, suggests that:
Time travel into our future is certainly possible.
Time travel into our past, however, is/will/can only be the case if our universe exists on/in/as a closed timelike curve which loops around, in which case we've got predestination on our hands in a nasty way, and we don't so much "invent" time travel as we inevitably play out the construction of a time machine and the travel into the past, "over and over".

That reminds me of an odd link between time travel and religious debates.

If I go into the past, e.g. to 1920, is the Second World War doomed to happen? Can I prevent it? Have I robbed people of free will by knowing what's going to happen "before" it happens? Does a hypothetical God's omniscience work the same way? Does omniscience, or any knowledge of a decision before it happens, really contradict free will?

 

[Mise]

C doesn't seem likely; I mean, look at all the threads here where they ask what time period you would visit if you had a tank or a machine gun or something, and how many people responded that they would try to take over the world with them, and then tell me that idea will never occur to anyone in the future.

Maybe they did? But there were "unforeseen circumstances" along the way. Such as America's late entry not coming late enough.

And how many lunatics have claimed to be from the future, only to be institutionalised

Personally I'd apply the anthropic principle to this -- if the past were altered by some time travel, we wouldn't find it odd, because it would be our past.

 

[Masquerouge]

FTL travel is certainly related to time-travel.

Current physics, as I understand it, suggests that:
Time travel into our future is certainly possible.

I'm linking two things from your post that you didn't link, but that's related to my question.

Is FTL linked to travel in the future, or travel in the past?

Basically I want to know if the FTL they have in pretty much every sci-fi material is a theoretical impossibility (we will NEVER be able to go from point A to point B faster than light) or a technological one (we currently don't know how to go from A to B FTL).

 

[xienwolf]

Look at wormholes and theories about space-time folding and you will see that it is technically possible to arrive at a location before light does, without traveling any faster than light (just taking a different path).

EDIT: Mildly upset nobody has any comments on my earlier post I was hoping someone might find a logical failure with it at the least so I could return to the thought process

 

[bob bobato]

I alwasy assumed that if travel back in time were possible, they would have gone back from when it was invented to now and told us.

Maybe they have; ever heard of someone being "ahead of their time"?

 

[Masquerouge]

Look at wormholes and theories about space-time folding and you will see that it is technically possible to arrive at a location before light does, without traveling any faster than light (just taking a different path).

But wouldn't wormholes and/or folding, by allowing information to arrive at their destinations faster than light, create some paradoxes?

 

[xienwolf]

I cannot think of what paradox is possible through this method. You are merely arriving before certain aspects of the information will manage to. Nothing is being changed in particular, so no Paradox comes readily to mind. It would be roughly equivalent to splitting a laser, bouncing part of it off a mirror, and then recombining the two at some later point. There is a shift, but no paradox.