# Time Travel

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Aperently, theoretically, with the use of wormholes and negative energy, and all that shtufff, it could be possible one day to create trips back in time.

Here is an explaination of why i dont understand how this works:

I would beleive that once traveled back in time, you would obviously do something that would change the path of the future. Now, in this new future, you might not creating a time machine, so you wouldn't have been able to change the past, so you would have actually created the time machine, and .... yeah.

Looking past this problem, I would beleive that changing the past could create either a time machine earlier, or later. Now, if we loop back to the past in either of those scenarios, we alter the past, and the time in which civilization creates the time machine would continually change. Eventually, the only possibility is that the loop continues until we have a universe in which the time machine is never discovered.

Looking past this looping problem, each time we would make a loop to the past, we are allowing some radiation to enter in with us. After thousands or maybe even millions of these loops (we aren't limited timewise if time keeps being "reset") there would be waay to much radiation and life would die out.

These problems seem pretty prominent in my eyes, but im sure that some of you out there may provide a better angle or new knowlegde on this topic to help me better understand it. A solution that i believe i have heard before, is that when traveling back in time, you actually enter a whole different parallel universe, seperate from the original one, but similar in many ways. This i believe would solve the problem, buuut how exactly would that work.... I think i have somewhat of a grasp on these concepts, but want someone to clarify.

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It's like the famous time travel conundrum: You travel to the past to before you were born and accidentally kill your mother. So if you did, then you don't exist in the future. But if you don't exist in the future, you couldn't have gone back to the past to kill your mother. But then you do exist. But if you do exist, you did go back to the past and kill your mother . . . Etc. Etc.

So is there a fundamental law of physics which prevents time machines? Or one which permits time machines but somehow prevents altering the past? I don't think any physicists has an answer. Or at least she/he doesn't have one which has been verified by empirical evidence.

I like Hawking's comment that there is empirical evidence that time machines are not possible. If they were, we would be visited by tourists from the future.

By the way, according to special relativity, we experience time travel into the future (in tiny amounts) all the time. See link:

http://www.marksmodernphysics.com/index.html and click on Its Relative

Edited by I ME
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Hi I ME,

At the end of the article it is said

" But we must be careful here. According to special relativity, this time travel is a one-way trip “You may be able to buy a round-trip ticket to (outer space),” wrote relativists Edwin F. Taylor and John Archibald Wheeler in Spacetime Physics, “but you get only a one-way ticket to the future.” So you can (and do) travel into the future, but you cannot travel into the past."

Is there any explanation to "Why it is a one-way ticket" ?

Thanks.

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Is there any explanation to "Why it is a one-way ticket" ?

We are continuously traveling into the future one second every second but according to relativity the rate at which time ticks are relative the observers frame of reference, as such an observer accelerating or in a different gravitational field or propagating with a high speed relative another observer will measure a different rate of ticks between the two observer's clocks. So one observer could age only a few years during a long space trip while plenty of years could have passed on Earth for the other observer.

There is however no way back, we can't travel backwards in time, only slow the rate how time passes relative other observers. While the space traveler has aged less during his time travel into the future, he has never the less aged too, he can't undo this ageing or go back to the time when the journey started.

Edited by Spyman
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Spyman is correct. Per special relativity, how fast you age depends on your relative motion. But you still age. Time still moves forward, albeit at a different rate (depending on relative motion). So this particular effect is a one-way trip forward in time.

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So, since we just can't really know how the time paradoxes work, is the hypothesis that traveling back in time will just open up a parallel universe where you will then preside the best explaination? or is there another easier way around the above stated problems with time travel?

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Hi Spyman,

Yeah but,

Why is the idea that "time travelling back to the past is possible" so rampant. Even to the extent of Science checking out the possibilities, like I ME quotes "Mr.Stephen Hawking saying that- there is empirical evidence that time machines are not possible."

I mean how did this idea come into being? i.e. on what scientific basis, did scientists feel that time travel backwards to the past is possible?

Thanks.

Edited by Anilkumar
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I mean how did this idea come into being? i.e. on what scientific basis, did scientists feel that time travel backwards to the past is possible?

I don't know, I was never any good in history and the technical parts of how it might be possible with relativity theory I better leave for the experts but in a simplified view: we can move freely in three space dimensions and we know that we are moving forward in time, so it's not that far fetched to imagine a controlled displacement in a time dimension.

So, since we just can't really know how the time paradoxes work, is the hypothesis that traveling back in time will just open up a parallel universe where you will then preside the best explaination? or is there another easier way around the above stated problems with time travel?

Paradoxes are caused by impossible situations, so either time travel like in movies, are impossible or there is some mechanism preventing paradoxes, alternative universes is one popular explanation but there exists others, like this one:

The Novikov self-consistency principle, also known as the Novikov self-consistency conjecture, is a principle developed by Russian physicist Igor Novikov in the mid-1980s to solve the problem of paradoxes in time travel, which is theoretically permitted in certain solutions of general relativity (solutions containing what are known as closed timelike curves). Stated simply, the Novikov consistency principle asserts that if an event exists that would give rise to a paradox, or to any "change" to the past whatsoever, then the probability of that event is zero. In short, it says that it's impossible to create time paradoxes.

http://en.wikipedia.org/wiki/Novikov_self-consistency_principle

Edited by Spyman
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It's like the famous time travel conundrum: You travel to the past to before you were born and accidentally kill your mother. So if you did, then you don't exist in the future. But if you don't exist in the future, you couldn't have gone back to the past to kill your mother. But then you do exist. But if you do exist, you did go back to the past and kill your mother . . . Etc. Etc.

So is there a fundamental law of physics which prevents time machines? Or one which permits time machines but somehow prevents altering the past? I don't think any physicists has an answer. Or at least she/he doesn't have one which has been verified by empirical evidence.

I like Hawking's comment that there is empirical evidence that time machines are not possible. If they were, we would be visited by tourists from the future.

By the way, according to special relativity, we experience time travel into the future (in tiny amounts) all the time. See link:

http://www.marksmode....com/index.html and click on Its Relative

Time is just a periodic measurement of a motion. I could easily replace the word second with something such as "per 10 swings of a that pendulum". However, everyone uses the same "pendulum" and time is thus perceived as a given of the universe. So, the only true to actually time travel would be to re-arrange all matter and energy in the universe to a state it previously was.

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You all have a fundamental misunderstanding of the problem. There is, in fact, no paradox.

Distance(space) is the separation between objects within a state. Similarly, Duration(time) is the separation between states. Think of a state as a snapshot of the universe. We're going to take that snapshot and all others and place them on a movie reel. The thing you guys don't understand, is that you're following the actor in the movie rather than the timeline of the movie itself.

If you travel into the past, you were there the one and only time it happened. While you experience it twice, the event only happened once. The present and the future are the result of any future time travel; you cannot change the past.

http://blogs.discovermagazine.com/cosmicvariance/2009/05/14/rules-for-time-travelers/

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You all have a fundamental misunderstanding of the problem. There is, in fact, no paradox.

Distance(space) is the separation between objects within a state. Similarly, Duration(time) is the separation between states. Think of a state as a snapshot of the universe. We're going to take that snapshot and all others and place them on a movie reel. The thing you guys don't understand, is that you're following the actor in the movie rather than the timeline of the movie itself.

If you travel into the past, you were there the one and only time it happened. While you experience it twice, the event only happened once. The present and the future are the result of any future time travel; you cannot change the past.

http://blogs.discovermagazine.com/cosmicvariance/2009/05/14/rules-for-time-travelers/

With all due respect, I think making the statement that everyone else is wrong and you are correct without any evidence whatsoever seems a little arrogant.

Until we can build a timemachine, if that's even possible, and then actually test your view of timetravel, we are not able to discern what would happen and distinguish between possibilities.

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Aperently, theoretically, with the use of wormholes and negative energy, and all that shtufff, it could be possible one day to create trips back in time.

Here is an explaination of why i dont understand how this works:

Or maybe not -- those things would be absurdly difficult in real life, not at all like in scifi. However, if you could make a closed timelike loop I don't think you could send messages back in time before the point at which you built the loop -- because there would not be any closed timelike loop there to send things back to, at that time.

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With all due respect, I think making the statement that everyone else is wrong and you are correct without any evidence whatsoever seems a little arrogant.

Until we can build a timemachine, if that's even possible, and then actually test your view of timetravel, we are not able to discern what would happen and distinguish between possibilities.

It's in the maths of General Relativity. It's also from basic philosophy. Four-dimensionalist B-theory of time(A theory has been effectively destroyed by physics) shows that I am correct. Any basic pop-sci book containing General relativity would give you the spacetime raisin-bread illustration and a similar discussion to the one I provided, but it would probably not be in the context of time travel.

So, no, it's not arrogant to explain modern physics in a way that people can understand it.

edit:

Even if there wasn't a commonly accepted theory, my explanation would be vastly superior since mine removes the paradoxes that yours creates.

Edited by ydoaPs
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You all have a fundamental misunderstanding of the problem. There is, in fact, no paradox.

Distance(space) is the separation between objects within a state. Similarly, Duration(time) is the separation between states. Think of a state as a snapshot of the universe. We're going to take that snapshot and all others and place them on a movie reel. The thing you guys don't understand, is that you're following the actor in the movie rather than the timeline of the movie itself.

If you travel into the past, you were there the one and only time it happened. While you experience it twice, the event only happened once. The present and the future are the result of any future time travel; you cannot change the past.

http://blogs.discove...time-travelers/

so if time travel is possible on day, not theoretical, then at one point already in time, there were time travelers even if they haven't been born yet to make that time travel, simply because they existed for that specific moment in time which cannot change. The problem is, i cant see how that would get started. The time travel would have to create a future in which the person in the time machine exists and is traveling back in time to the point in which he ... already traveled back in time... yeah, which might not be too hard to believe... it think. Its like a time loop i suppose. but how does the loop get started in the first place? Does the universe just initially realize that humanity is going to invent the time machine, and then include the time traveler in its next "snapshot"? This just seems like another paradox to me.

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so if time travel is possible on day, not theoretical, then at one point already in time, there were time travelers even if they haven't been born yet to make that time travel, simply because they existed for that specific moment in time which cannot change. The problem is, i cant see how that would get started. The time travel would have to create a future in which the person in the time machine exists and is traveling back in time to the point in which he ... already traveled back in time... yeah, which might not be too hard to believe... it think. Its like a time loop i suppose. but how does the loop get started in the first place? Does the universe just initially realize that humanity is going to invent the time machine, and then include the time traveler in its next "snapshot"? This just seems like another paradox to me.

The present is no more real than the past, just as your spacial position is no more real than 4 feet left of it. All states exist equally.

Time travel is all about geometry of spacetime as a whole. Where there is a closed timelike curve(a time machine), there is a closed timelike curve; where there isn't a closed timelike curve, there isn't a closed timelike curve.

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It's in the maths of General Relativity. It's also from basic philosophy. Four-dimensionalist B-theory of time(A theory has been effectively destroyed by physics) shows that I am correct. Any basic pop-sci book containing General relativity would give you the spacetime raisin-bread illustration and a similar discussion to the one I provided, but it would probably not be in the context of time travel.

So, no, it's not arrogant to explain modern physics in a way that people can understand it.

edit:

Even if there wasn't a commonly accepted theory, my explanation would be vastly superior since mine removes the paradoxes that yours creates.

Well ydoaPs, if you read my posts again, slowly and carefully, you might discover that I did not say it was "arrogant to explain modern physics in a way that people can understand it" nor did I say something against GR or basic philosophy.

There was nothing wrong with your explanation except the "you are all wrong" part.

AFAIK, and contrary to what you seem to claim, the Arrow of time and the question: "Is there a single possible past?" is still some of the major unsolved problems in physics.

Please show me where I did present an explanation which creates paradoxes or where I did show "a fundamental misunderstanding of the problem".

Edited by Spyman
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think of it like this: earths atmosphere is the international date line, space is one day, earth is another, if you travel over the international date line, you can end up arriving before you chronologically left, therefore, if you hit the black hole at the right angle, you will be caught up in a giant gravitational slingshot and be sent round the earth fast enough to arrive before you cronologically left

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• 4 weeks later...

Since the total amount of energy in the Universe is a constant at any one time, then time travel would violate this law? So maybe it is this conservation of energy law which prohibits time travel?

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I wonder if you move forward or backward in time the earth will not be where it was when you left. You might find yourself in the emptiness of space!

Edited by TonyMcC
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If someone went back in time then would the future where he's from cease to exist? No future authority would be able to send 'time cop' to drag him back to the future.

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This is nonsense solution going back to the past.

What is our living? Our living is consists of mind and matter.

We can go to the future physically well.

Back to the past is a problem.

We can make the past from huge amount of past information - like Matrix movie.

Then we can go to future, and go back to the past.

When someone goes into the time machine, he can enjoy all the time period.

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As wondeful and enticing as it sounds i personaly believe time travel is not possible. In the sense of moving faster than time allotted maybe in a since. but to travel in the past to events that have already happend, is logicly impossible unless there is some kind of black hole time rip but even that i do not believe would allow changes in the current time. Now again i am opposed to time travel but what if people visited earth 1000 years ago helped the egyptians bulid the pyramids, palenco and ufo's are actually time machines from our future bretheren. But of course due to goverment regulations time travel is highly restricted and used for goverment research only. Or just aliens checking on the ant farm... The world may never know just the future??

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As wondeful and enticing as it sounds i personaly believe time travel is not possible. In the sense of moving faster than time allotted maybe in a since. but to travel in the past to events that have already happend, is logicly impossible unless there is some kind of black hole time rip but even that i do not believe would allow changes in the current time. Now again i am opposed to time travel but what if people visited earth 1000 years ago helped the egyptians bulid the pyramids, palenco and ufo's are actually time machines from our future bretheren. But of course due to goverment regulations time travel is highly restricted and used for goverment research only. Or just aliens checking on the ant farm... The world may never know just the future??

I can describe Time Travel with one word… Impossible.

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Well, I guess I'll put my two cents in.

The universe is a sea of time, all movement therein is time travel. This is what I call "Horizontal" time travel. In this type of time travel going backwards and forwarda is not only possible but very probable. It is similar to a VCR tape going back and forth. The only difference is that the tape is two dimensional and we are three dimensional. We move back and forth in time and don't know it because our thoughts and actions are always within the prespective time frame. That is to say that all of this is but a rerun and everything has happened before and again and again. within my theory "infinite theory" it is possible for mass to quantum leap from one point in space time to another. This is also a "horizontal" time movement. Atoms appear and disapear as they define present moments of time by converting future distance into past distance space. All things are a matter of relative perspective within infinite scales except the speed of light. This is the only constant and seperates and defines our universe from the ones around it.

The type of time travel being discussed on this forum is what I call "vertical" time travel. It has to do with going into the past and the future. Every instant of time has it's "time signature" past, present, and future. It can be calculated by the size of the universe at any given point in time. The speed of light is infinite. The present time signeture is the amount of time it takes for light to travel one on edge of the universe to the other. Like the counter on an old cassette deck measuring the inches on the tape back and forth. Light records the distance and places everything in it's proper order accordingly. There are two ways to time travel vertically as far as I can predict. In the first instance:

It is possible to isolate the time stream of the present and project it into the future or the past where you do not exist in your present state. Since you cannot live without your physical body (as far as we know) you can only project a small percentage of the time stream around you. The past and future is real and a part of your present, but you will only experiece it as a ghost and in a dream like state.

In the other instance you'd have to remain in the forward time state that we are in while shrinking or expanding the universe around you. This would require existing in one universe while creating other versions of the universe around you. Hence, parallel universes that expand and contract to the point you wish to enter in and reform a new future.

This may seem impossible to the casual observer but some believe that every possibility already exists. If this is true then this type of time travel is simply a matter of marking your current universal time signature and traveling to another that already exists inbetween the frames of time that we currently experience. This instance of time travel leads back to the question of "why have'nt time travelers visited us before? Personally, I think they have. I'm sure they try and blend in and enjoy the time frames at hand. If they are here than they must have traveled from the future, because the technology does not exist yet and you cannot explain how a cell phone works to a cave man. However, stories that contain magic wands have been around for a long time. Poof! your insane! LOL

Well, that's my take on time travel. I hope at the very least it gives somebody a little food for thought. And if your a time traveler, maybe you could give us all a better insight than mine. Just bring your two cents worth and have no fear of the rubber room or the straight jacket. I think the world is ready now.

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• 2 weeks later...

Well lets get this straight and clear and this is the last time im going to say anything about this topic again on this forum, the time travel crap needs to stop, time is a living force, very constant and has been here before you and will be here long after the bugs have eaten your corpse, time cannot be manipulated, you would have to make dead people be reborn and redo all there deeds over again and people would have to go back and replay everything they did from long ago, and as for future travel we cannot do that bvecuase we have yet to reach that point in reality, we cant skip and fastforward reality, and we cannot redo or be in a time that was before, time cannot bbe manipulated which is what you guys are trying to speculate, just like we cannot add a year to our lives or stop drinking water or something with the same chemical makeup and expect to live much longer, God has put absolute laws to limit mans influence on certain things, and as for the so called proof of time travel through the high speed airplanes; thats nothing more than your brain messing with you, you have not traveled through time, thats called a time lapse, lets live in reality here and grow up, take time to get your stuff in order with relatives, famiy, and friends before its too late because time keeps ticking.

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