Time Travel

so... do you think it is theoretically possible? if so, which theory do you think seems the most likely, or do you have your own theory?


I personally, don't believe it is possible in the sense that people think of it. My reasons for this is because time is something we created, it has no actual meaning besides what we give to it. Still I can't help but to spend my spare time thinking on the subject. I suppose if it were possible I believe the infinite universe theory would seem the most likely. So if we were to go back in time we couldn't actually change anything, because which ever time stream we ended up the things that occurred there would be one of the infinite outcomes that was supposed to already have happened. I'm starting to lose myself here so I'm going to give up on it for now. I guess I am talking more of travel between parallel universes more than time travel but I think it may be very similar....


ok, i don't know if that made any sense, I'm hoping I can get into a very theoretical debate here, I'm hoping there will be no criticisms on peoples views on the subject since it is all completely theoretical anyways.

Time is the most confounding, interesting concept everz.

I am posting this to remind myself to come back to this. I'm currently on the side of quantum mechanics... but I may consult some physics...

Where are the physics nutters at?

You may have lost yourself, but I'm still with you. Time travel is a subject very near and dear to my heart, and I agree, it may be attainable but not the way it looks in Back to the Future.

The crux of the issue is that time, as a spatial dimension, does not proceed in the straight line that we perceive, but rather moves through the dimension above it, usually referred to as causality (or probability if you're a Douglas Adams fan). Thus to travel to a discrete point in time would make you "lose your place" on the axis of causality - the travel wouldn't necessarily be the difficult part, but the getting back would.
A less eggheaded way of putting it is, yes you may go back in time, but because you're there you'll end up in a different timeline.

But AgentSH, you say, what about traveling to the future? The same principle would apply, I suppose. Traveling forward in time is theoretically possible, but you may not necessarily end up in the same universe as you would have if you'd just gone cryogenic and waited a few thousand years.

That's the opinion of someone who cheated his way through physics class. I'd like to present another issue: if time travel is possible, shouldn't we have time travelers from the future among us now?

Frankly, I'm not sure how you can have a debate about this kind of thing when none of us are qualified to really discuss it in detail, but here's my opinion on "time travel."

The short of it is that no, simple "time travel" is very, very unlikely to even be plausible, much less possible - with or without special relativity with respect to *everything*. Obviously I am not an astrophysicist, but it's my very basic understanding that "time travel" generally refers to going back in time (I'll ignore going forward in time for now) without taking into account one's position relative to the other dimensions (space in general).

As far as going backwards, there needs to be some unified definition for "travel" as one person could, theoretically, use a wormhole or other curved-space architecture so as to end up at a place in both time and space that is impossible for another person to reach while complying with general relativity and whatever our "normal" number of dimensions are. That is to say that the person who used a wormhole would still be traveling forward in time (relative to themselves), but would simply get there before it was possible to do so by general means. To me I wouldn't call this "time travel." More like cheating. =) But again, IANAAP, so I'm not qualified to present anything as more than a basic opinion. Wikipedia has LOTS of stuff on cheating time travel. None of which is like what we see in movies or read in books.

With respect to traveling forward, I can see how that would be seen as plausible, albeit not in the way it happens in movies. This would be accomplished by simply traveling forward in time relative to others, but not yourself. That is to say that if I were to travel at or near the speed of light in one direction for 25 years, for example, then travel immediately back to earth, I would be a sum of 50 years older (25yrs each way = 50 total). However, as I'm sure people have read from Einstein's general relativity, the person observing this ~50 year journey would have actually aged much beyond the 50 years of the participant. That's time dilation. It still doesn't seem like "time travel" as we see it in movies as it is more of a cheat of observers and not yourself. It's also not instantaneous, which always seemed like a more reasonable way to do it. Although if I had the means I wouldn't mind giving up 50 years of my life to see what the world looks like in the future.

I'm curious as to what others say regarding the science. But RRob, you might want to start another thread, for the sake of comparison, as to what people think about fictional time traveling. That would be quite interesting as well. =)

EDIT: AgentSH beat me to posting about M-theory and divergent universes in the multiverse structure - which is what I believe he's referring to? Also, I didn't think that you could go "back" by getting to a different layer, but rather would end up in a different time-line altogether.
EDIT2: I'm waiting for someone to mention punching a hole in the fabric of space-time.

Originally Posted by AgentSH

That's the opinion of someone who cheated his way through physics class. I'd like to present another issue: if time travel is possible, shouldn't we have time travelers from the future among us now?

That's the thing. How would one arrive at their destination in time? Appear from thin air? A wormhole perhaps? What happens to the place they left? It obviously can't cease to exist because they left something behind (the whole universe that they had been in)

To travel, you are basically moving energy/matter around, and energy cannot be created or destroyed, which means there must be a connection for it to pass from one to the other - or both times must exist, in other words.

The question I think is this: who's time can one travel to? Their own time in the past? Their own time in the future? Or the past or future of separate universes, which have no direct correlation to the one which they left?

Originally Posted by AgentSH

I'd like to present another issue: if time travel is possible, shouldn't we have time travelers from the future among us now?

Don't we have a term for the people that have time traveled already? "Cucu"

I wish I could jump in and discuss the topic on some intellectual level but my physics level does not go near that in depth. The thoughts of time travel are fascinating though! I can't say I haven't daydreamed about it. But if you guys COULD time travel, ethically speaking, would you really want to?

Originally Posted by Spades

(snip)

EDIT: AgentSH beat me to posting about M-theory and divergent universes in the multiverse structure - which is what I believe he's referring to? Also, I didn't think that you could go "back" by getting to a different layer, but rather would end up in a different time-line altogether.
EDIT2: I'm waiting for someone to mention punching a hole in the fabric of space-time.

Thanks, actually that's what I meant to convey, by definition you would be in a different timeline. You put it more clearly though.
But, shame on you. I'm not an astrophysicist either, but I still feel qualified to discuss time travel because it is awesome and sexy.

As for punching a hole in the fabric of space-time, who's to say it's one solid piece now?

Originally Posted by seraphiel

That's the thing. How would one arrive at their destination in time? Appear from thin air? A wormhole perhaps? What happens to the place they left? It obviously can't cease to exist because they left something behind (the whole universe that they had been in)

If he's talking about M-theory style time travel as I suspect then it's not moving through space so much, as going to a different plane (with a different set of Laws of Physics). It's more like "dimensional travel" than "time-travel."

Originally Posted by seraphiel

To travel, you are basically moving energy/matter around, and energy cannot be created or destroyed, which means there must be a connection for it to pass from one to the other - or both times must exist, in other words.

That only applies to general relativity and neither special relativity nor quantum mechanics. I don't have the credentials to answer your real question, but I do know that at the very least the first law of thermodynamics only applies to general relativity.

EDIT:

Originally Posted by AgentSH

...I still feel qualified to discuss time travel because it is awesome and sexy.

Pfft. I find that the curves on "time-travel' are not to my liking. She is an awesome mistress, but a beached whale as well. =P

Yo dawg, I herd u liek edits so I put an edit in your edit so you can edit while you edit! (means I fixed something again.)

Originally Posted by Spades

If he's talking about M-theory style time travel as I suspect then it's not moving through space so much, as going to a different plane (with a different set of Laws of Physics). It's more like "dimensional travel" than "time-travel."

That only applies to general relativity and neither special relativity nor quantum mechanics. I don't have the credentials to answer your real question, but I do know that at the very least the first law of thermodynamics only applies to general relativity.

Ok, in that case, would you be able to travel and live to tell about it, or know that you traveled? General relativity does matter on the macro level - who's to say you won't go to another dimension that causes you to be obliterated into your basic particles? Unless you could take a 'bubble' of your own dimension which governs your own existence, or be able to maintain your consciousness in a possibly different form from the one you are used to.

Quantum mechanics (not to be confused with temporal mechanics!) is great for particles, but it becomes confusing with macro level beings, as I think Schrödinger's cat has shown.

Originally Posted by seraphiel

Ok, in that case, would you be able to travel and live to tell about it, or know that you traveled? General relativity does matter on the macro level - who's to say you won't go to another dimension that causes you to be obliterated into your basic particles? Unless you could take a 'bubble' of your own dimension which governs your own existence, or be able to maintain your consciousness in a possibly different form from the one you are used to.

Quantum mechanics (not to be confused with temporal mechanics!) is great for particles, but it becomes confusing with macro level beings, as I think Schrödinger's cat has shown.

First, how would you define "travel and live to tell about it?" Do you expect to come back within a reasonable frame of space-time and meet the people you knew before (even if according to general relativity they had progressed through time at a rate consistent with you)? As you said it depends on where you end it. "Time-travel" is, inherently, going to change your position in space UNLESS you use an M-theory hack (which is what we've been discussing).

Regarding "general relativity at the macro level:" wut? General relativity hasn't been unproven to our space-time simply because we don't know enough about our space-time to disprove it (but it's doing fairly well so far at a basic level). I'm not sure how we would logically apply GR to a different universe that is only theorized on paper. I'm sure that's what you're getting at =) and I have no idea. One hopes that gravity would apply in other dimension-groups and universes, but it's possible that finding out would not be fun in the least. =)

Also, going back to the "maintaining consciousness" (as an individual, not being awake), that goes back to the conservation of matter thing. If you can get there, I would expect you to maintain the same form (but hey, I'm still not an astrophysicist). You're still within the same multiverse so things would be okay regardless of whether GR/thermo applied. Right?

To make an analogy. You have a sandwich with three pieces of bread and two layers total within the sandwich. We'll say that there's a slice of salami maintaining each layer's integrity. If you took one piece of salami and "magically" moved it up a layer, it's still salami. You may have completely compromised the layer it moved to - or moved into a singularity, like peanut butter - that you didn't know existed, but you still have a sandwich with two layers. You just have ... a really gross sandwich. Oh, and now it's weightless.

[/worst analogy ever]