Time travel... is it really possible?

[gallardo]

I've heard that general relativity predicts that time travel is possible, yet I can't seem to get my head around that concept.

The grandfather paradox is what started it for me.

For the few that don't know the grandfather paradox, it's about going back in time and murdering your grandfather before he conceives your father. Thus you cannot be born and thus you cannot go back in time and murder your grandfather. Paradox.


I can see only 2 ways around the paradox:

1) You don't go back in your own time, but merely in an alternate reality and screw things over there.
2) The moment you go back in time you "shield" yourself from the changes you make, becoming separated from your timeline.


Either way, there's a problem. You're not going back in time, but rather going back TO a previous time. Why? Because time didn't go back for you. For you time went forward... just the environment changed, like everybody on the planet playing this giant prank on you. I mean... what would be the difference between what we assume to mean going back in time and arranging all of the atoms in the universe to a previous state? None as far as I can see. In both cases the environment becomes identical to that of a previous state, but to you time still goes forward. You are in the year 2008, you turn the time machine on and one second later you are in what appears to be 1950.

My question is this: how can general relativity prove that time travel is possible when in essence time still goes forward for the observer, the traveler?


What are your thoughts on the subject? What would you do if given the opportunity to travel through time? What if you could do it only once? What if you couldn't return to your time? What if you could do it at will?


If I could do it only once and/or couldn't return I'd try and make the most money out of it in the shortest amount of time. Either short Lehman stock or win the lottery.
But if I could do it at will... then I'd have a little fun. Probably screw things up pretty good.

[MikeB12]

here's a video from one of the guy's that's always on "The Universe" talking about it http://www.youtube.com/watch?v=X02WM...eature=related

[Xel'Naga]

With our current theories, forward time travel (in the future) is possible and has been measured (and the results are according to the theory), but time travel in the past is is impossible.
However, we don't know if the current theories are completely true. Newtonian mechanics was considered true until it was noticed that it fails in extreme conditions(atomic scale, speeds comparable with c and so on).

[Frisch]

Time travel is easy....just take the next flight to Australia, and you have done it. ( That's traveling into the future for you. )

[adamsleath]

requires faster than light travel which is theoretically impossible....but then our understanding of the universe is puny and limited (i can only speculate at the vastness of the unknown)

as a mass approaches the speed of light it's mass increases exponentially..according to einsteins rules....and yet time travel is possible according to einsteins relativity theory

paradoxes that could occur if time travel is possible...well, the alternate reality idea is as good as any, and just as unproveable.

but remember, whatever you do, DONT GIVE BIFF THE SPORTS ALMANAC!

as for the grandfather paradox; perhaps reality would just change around the traveller to reflect the 'new' space-time events...by which i mean if you killed your own grandfather you would instantly cease to exist as space-time alters around you to reflect the new altered 'version' of space-time...."Stargate Continuum" shows this kind of possibility....lots of different sci-fi views on time travel.

Isaac Asimov was writing sci-fi stories about infinite alternate realities ("infinities" he called them) and time travel back in the 50's/60's.

perhaps the only way to travel beyond or outside of space-time is by leaving one reality and entering another. We are bound as objects in space-time, i think, and we can travel forward either faster or slower than other objects in a relative manner, but as for going backwards in time, relative to other objects in the same space-time "continuum" - i dont think it is possible.

[MikeB12]

at least not until we can harness the power needed to create worm holes... it's theorized that the power needed to produce such an event is equivalent to all the energy stored in a star, and releasing all at once.. so even if we reach a point where we can produce large amounts of anti matter, the possibility of producing enough power for such an event is impossible for anything in the near future. not to mention even if we could ever store enough energy for an event like that, would you even want to be in the same star system when it happened... talk about blowing ourselves up.. that makes the atom bomb look like a snap crackle pop from this moorning's bowl of rice crispies.

[Sparky]

If time travel were possible, there are a few things I've done that I want to go back and correct

[kuhla]

If time travel were possible, there are a few things I've done that I want to go back and correct

You will never time travel. If you ever time traveled and went back in time to fix those problems you would not be mentioning them now because they never happened. If the past was changed, we would not remember it.

[tomashcraft]

i think with a flux capacitor anything is possible

[Sparky]

You will never time travel. If you ever time traveled and went back in time to fix those problems you would not be mentioning them now because they never happened. If the past was changed, we would not remember it.

I know.

[MikeB12]

time dilation and time travel are different concepts....

anyone who's smoked a spliff has experienced time dilation

[YukonTrooper]

The question is unanswerable. We simply do not know enough about the universe. Asking humanity to decipher the concept of time travel, is like asking a monkey to to land a Chinook helicopter on the back of an aircraft carrier, in a hurricane, with no hands, while blindfolded.

[Eldonko]

I agree!

i think with a flux capacitor anything is possible

[Zytek_Fan]

It IS possible, BUT it would defy many laws.

[Knight203]

The question is unanswerable. We simply do not know enough about the universe. Asking humanity to decipher the concept of time travel, is like asking a monkey to to land a Chinook helicopter on the back of an aircraft carrier, in a hurricane, with no hands, while blindfolded.

The thing is with the right training and alot of luck that could happen so with a lot of research and a hell of a lot of luck we might just do it hell look where we have gotten in the past 100 years whos to say Now that in the future time travel is impossible? Who knows some one from 10,000 years in the future could come back in time and give us the knowledge to build a time machine now. Yet another paradox

[YukonTrooper]

The thing is with the right training and alot of luck that could happen so with a lot of research and a hell of a lot of luck we might just do it hell look where we have gotten in the past 100 years whos to say Now that in the future time travel is impossible? Who knows some one from 10,000 years in the future could come back in time and give us the knowledge to build a time machine now. Yet another paradox

Exactly. If time travel is indeed possible, it is realistic to think of it as achievable by an intelligent species such as ourselves; however, even if possible, with our currently feeble understanding of the universe, it is far beyond us.

[STEvil]

Possible? Nah.

Speed of light related to it? Nope.

Relativity really relative? Not likely.

[skippy1729]

If time travel is possible, where are all the tourists from the future?

Skippy

[Hoboclese]

as has already been said its unlikely that time travel into the past is possible due to the resultant paradoxes and lack of visitors from the future. But there is no reason to believe that time travel into the future is impossible, its just that once you got there you might be stuck.

[ahmad]

If time travel was possible for humans, it would mean that every second of every day from the beginning of time till the end of time is constantly repeated forever, and anyone living in any giving second maybe able to travel to any of those seconds, therefore affecting the future in that travel, and affecting the past, which then affects the current situation which affects the future.. which makes it impossible.

People can dream, which is why I am going to sleep right now.

Possible? Nah.

Speed of light related to it? Nope.

Relativity really relative? Not likely.

[jimmyz]

If time travel is possible, where are all the tourists from the future?

Skippy

In the ufo's people have been reporting for centuries.... those are time tourists.

[Shocker003]

Well if time travel is possible, i guess collecting lotto winning numbers and best stock woun´t be a bad idea. I will Like to travel say from 2030 to 2007 to win 30,000,000 euro in lotto. Well Just like our forefathers thought that flying to the moon is impossible, time travel will happen when we find the way around it. I trust humans at solving unknown issues.

[hollywood]

Time dilation and space flight

Time dilation would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed retards the rate of passage of on-board time. That is, the ship's clock (and according to relativity, any human traveling with it) shows less elapsed time than the clocks of observers on Earth. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1 g acceleration would permit humans to travel as far as light has been able to travel since the big bang (some 13.7 billion light years) in one human lifetime. The space travelers could return to Earth billions of years in the future. A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle.

A more likely use of this effect would be to enable humans to travel to nearby stars without spending their entire lives aboard the ship. However, any such application of time dilation would require the use of some new, advanced method of propulsion. A further problem with relativistic travel is that at such velocities dispersed particles in the rarefied interstellar medium would turn into a stream of high-energy cosmic rays that would destroy the ship unless extraordinary radiation protection measures were taken. Strong electromagnetic fields that could ionize and deflect any interstellar matter has been suggested as one way to avoid these potentially disastrous consequences.

Current space flight technology has fundamental theoretical limits based on the practical problem that an increasing amount of energy is required for propulsion as a craft approaches the speed of light. The likelihood of collision with small space debris and other particulate material is another practical limitation. At the velocities presently attained, however, time dilation is not a factor in space travel. Travel to regions of space-time where gravitational time dilation is taking place, such as within the gravitational field of a black hole but outside the event horizon (perhaps on a hyperbolic trajectory exiting the field), could also yield results consistent with present theory.

[BiFfMaN]

but remember, whatever you do, DONT GIVE BIFF THE SPORTS ALMANAC!

HEY!

[STEvil]

Time dilation and space flight

Time dilation would make it possible for passengers in a fast-moving vehicle to travel further into the future while aging very little, in that their great speed retards the rate of passage of on-board time. That is, the ship's clock (and according to relativity, any human traveling with it) shows less elapsed time than the clocks of observers on Earth. For sufficiently high speeds the effect is dramatic. For example, one year of travel might correspond to ten years at home. Indeed, a constant 1 g acceleration would permit humans to travel as far as light has been able to travel since the big bang (some 13.7 billion light years) in one human lifetime. The space travelers could return to Earth billions of years in the future. A scenario based on this idea was presented in the novel Planet of the Apes by Pierre Boulle.

A more likely use of this effect would be to enable humans to travel to nearby stars without spending their entire lives aboard the ship. However, any such application of time dilation would require the use of some new, advanced method of propulsion. A further problem with relativistic travel is that at such velocities dispersed particles in the rarefied interstellar medium would turn into a stream of high-energy cosmic rays that would destroy the ship unless extraordinary radiation protection measures were taken. Strong electromagnetic fields that could ionize and deflect any interstellar matter has been suggested as one way to avoid these potentially disastrous consequences.

Current space flight technology has fundamental theoretical limits based on the practical problem that an increasing amount of energy is required for propulsion as a craft approaches the speed of light. The likelihood of collision with small space debris and other particulate material is another practical limitation. At the velocities presently attained, however, time dilation is not a factor in space travel. Travel to regions of space-time where gravitational time dilation is taking place, such as within the gravitational field of a black hole but outside the event horizon (perhaps on a hyperbolic trajectory exiting the field), could also yield results consistent with present theory.

I think this is a misunderstanding. At a given time x and y exist in their respective places. If you move one very quickly (approaching "the speed of light") then each must still exist in their respective places given that they are physical matter. If they happened to overlap in their journey then one or the other must not be matter in order to occupy the same space at the same time.

Think of it as shooting an arrow (y) at "the speed of light" and it passing through your head (x). Given what the theory shows both the arrow and your head must be capable of occupying the same space at one time without damage to the other if time travel is possible due to speed.

Now, energy and matter occupying the same space at a given time might be a different issue all together....



Also to add to my previous post:

Reality relative? no.