Is (theoretical) timetravel possible without automatically creating a paradox?

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Originally Posted by Rocky

K good luck.

As for time travel, I would say it happens everytime we jump on a plane and enter a different timezone, as the outcome is different then what he originally had since we went through time.

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Are you kidding?

The time difference is something made up by humans because of the rotation of the earth. the day starts at a different time depending on your place on earth. First of all, you don't have to jump on a plain, jsut cross the Spain/Portugal border. Second of all, this isn't really timetravel is it... You're still in the same time... you just call it differently because of science.

If you go to a country where they use the muslim year calendar, you travel through time too? According to your "theory", yes. And that just doesn't make any sense in my opinion. :)

peace!

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Originally Posted by RagnaToad

Are you kidding?

The time difference is something made up by humans because of the rotation of the earth. the day starts at a different time depending on your place on earth. First of all, you don't have to jump on a plain, jsut cross the Spain/Portugal border. Second of all, this isn't really timetravel is it... You're still in the same time... you just call it differently because of science.

If you go to a country where they use the muslim year calendar, you travel through time too? According to your "theory", yes. And that just doesn't make any sense in my opinion. :)

peace!

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Right now, it is 10pm where I live. Are you going to try to tell me different? If I traveled to Florida, it would be 11pm. We live in different time eras, literally, which is why all the cool bands and stuff all start from the east coast and it takes awhile for us midwesterners to catch up with the times so to speak. :)


For further proof, I leave this as evidence that it can be the same time in multiple places, and that if we wish to travel to a certain time era, we can.

Yes I am going to tell you different.

It's not a different time where you live at all...
The sun is just in another place for you... The earth has the same age where I am as where you are.

If i were to go to a place where it is, say, 6 hours laters, would everything in my place be suddenly 6 hours further too? no. It would be just like it would be if I did not go to another place... Know what I'm saying?

What you believe to be "timetravelling" is not travelling through time. It's just travelling through space, and arriving at a place where the sun is on a different place in the sky.

If what you call is timetravelling, then taking a step of 1 meter is also timetravelling...
Since the sun would relatively be in a slightly different spot...

IMO, time travel is impossible. Think of it this way. From the perspective of the present, there is an infinite number of futures. By writing this post, I am choosing one future of literally infinite possibilities. If, in the present, you were to gain access to a time machine, and you went back in time, you would be branching the future into a different future (our present). Even just being there would be enough to change the future (present) unrecognisably. You could change the future (present) so that you never went back to the past, or indeed never existed. Thus, a paradox arises.

Consider the so-called Grandfather Paradox. Say you go to the past to kill your grandfather before he has met your grandmother. If you succeed, then you could never have existed. If you could never have existed, then you could never have gone into the past to kill your grandfather, and thus, you did exist, and you did kill your grandfather, and so on. That's a paradox, and that's why I think time travel is impossible.

I'm not so sure about future travel yet, though, but if you were to go into the future, and then come back, with that information in mind, wouldn't the 'natural' future (i.e. when it arrives normally), be different to the one you prematurely experienced?

Thus, it seems impossible, and this is without actually discussing the physical reality of time travel itself. How does a physical object move through time, and come back together on the other side. That's some trippy sh*t.

In my opinion, time travel backwards is going to be completely impossible. I think one of the arguments for it is the paradox argument (although using a parallel world theory can at least give a plausible counter to this). However, I don't think we can change anything that's already happened in our particular world with time travel, since it would have already happened.

However, if we look at it from a pure mechanical perspective, we see that this becomes impossible. In accordance with relativistic theory, an object that moves faster than the speed of light will have to move backwards through time. Basically, as you approach the speed of light, clocks will run slower (because light must move at the speed of light in ALL reference frames). Once you exceed the speed of light, this time dilation actually starts causing time to go in reverse.

Unfortunately, the force needed to accelerate grows with the effect of the time dilation, and it would take an infinite amount of force to accelerate something to the speed of light. This, to me, suggests that we won't be traveling backwards in time anytime sono.

Now, as for time travel towards the future, I don't necessarily see why not. Even if it is possible, I do think it would be impossible to go back, given what I stated above. However, my gut instinct says that it probably isn't possible. Although the existence of forward time travel would, to me, suggest that time isn't continuous and can be broken up into discrete units, which has its own interesting implications.

Though we mightn't ever have the technology for it, couldn't we go back in time by just travelling faster than the speed of light? Granted we wouldn't be able to go back to the present a similar way, but there could be a different way to do that. I speak of freezing the body and having it thawed out at whichever point in the future you want to be at. That actually strikes me as possibly being doable sometime in the not too distant future as advances in cryopreservation seem to be going along quite well.

As with the above, this next bit is pure speculation, but I think if someone did try to change the past, they'd **** up somehow and the events would be as we know them today. When time travel is possible (if ever) perhaps humans will be wise enough to not screw around with things that have the potential to possibly bite them in the ass so bad.

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Originally Posted by Silver

Though we mightn't ever have the technology for it, couldn't we go back in time by just travelling faster than the speed of light?

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The "faster than light" theory is just popular because light is what is fastest in our world. Why would a relative speed like that change anything about your position in "time"?

Not that I believe there is such a thing as "time", but I'll play along.

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Originally Posted by RagnaToad

The "faster than light" theory is just popular because light is what is fastest in our world. Why would a relative speed like that change anything about your position in "time"?

Not that I believe there is such a thing as "time", but I'll play along.

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Ragna, if you'll read my post, you'll see why that theory is popular, but I'll go into more mathematical precision. In a reference frame that is moving with some velocity, clocks run slowly. Specifically, they will run slower by a factor of sqrt(1-v^2/c^2), where v is the velocity of the reference frame and c is the speed of light. So, as the velocity of your reference frame approaches the speed of light, this term goes to sqrt(1-c^2/c^2) = 0. (This is the theory by which Ender survived so long in Speaker for the Dead+ if you've read the Ender's Game series. He stayed traveling at close to the speed of light for a very long time.) The problem is, once v exceeds the speed of light, you have that 1 - v^2/c^2 < 0, which means that this term is imaginary. Basically:

t_(in_frame) = t_(out_of_frame) * sqrt(1-v^2/c^2)

If we square both sides of the equation:

t_(if)^2 = t_(of)^2 * (1 - v^2/c^2).

Now, if v > c, then what we see is that (1 - v^2/c^2) is negative. I'll say -a = (1-v^2/c^2), which means that a is some positive value. So, we have:

t_(if)^2 = -a*t_(of)^2

So, this implies that if v > c, while the person inside the faster-than-light frame feels time moving forward, any observer in a different frame will see time moving backwards. This is where the theory of time travel comes from. Now, there are several holes in this. Firstly, only the square of the time observed decreases, not necessarily the time itself. Without squaring, the time dilation value is imaginary, which doesn't give any obvious intuition what would happen when the observed time is imaginary. Secondly, and most importantly, the force needed to accelerate an object follows a similar formula (the force needed is divided by the time dliation value, better known as the Lorentz factor). This means that once you're above the speed of light, the force needed to accelerate would also be imaginary (and the square of the forces would similarly be negative to an observer). However, most importantly, this implies that an infinite amount of force is required to accelerate something to the speed of light.

Shan'do Spike, when you post in these kinds of threads, it would really be best not to write as though you were copying straight out of a textbook. Not everyone is going to understand what v, c, t, and all of your subscripts stand for. It's fine for the people that study science, but the majority of the people that post here aren't studying to be physicists.

Having said that, I think you're trying too hard to simplify things. The situation is not as basic as you would lead us to believe, and if the problem was that simple, it wouldn't still be controversial.

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Originally Posted by M16

Shan'do Spike, when you post in these kinds of threads, it would really be best not to write as though you were copying straight out of a textbook. Not everyone is going to understand what v, c, t, and all of your subscripts stand for. It's fine for the people that study science, but the majority of the people that post here aren't studying to be physicists.

Having said that, I think you're trying too hard to simplify things. The situation is not as basic as you would lead us to believe, and if the problem was that simple, it wouldn't still be controversial.

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v = velocity
t = time
c = speed of light

Basic terms and abbreviations.

And isn't that just the theory of relativity, the stuff you're stating here?

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Originally Posted by RagnaToad

v = velocity
t = time
c = speed of light

Basic terms and abbreviations.

And isn't that just the theory of relativity, the stuff you're stating here?

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Yup yup, it is just the theory of relativity. M16: I'm not trying too hard at all to simplify things. I'm not even really simplifying things at all. I don't even personally believe it (because as I noted in my post, the time observed would be imaginary in direction, not necessarily negative). I was simply explaining to Ragna why moving faster than light => travel backwards in time is a popular theory.


And if you'll read the post again, I did define my terms that I thought were non-trivial:

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Originally Posted by Shan'do Spike

Specifically, they will run slower by a factor of sqrt(1-v^2/c^2), where v is the velocity of the reference frame and c is the speed of light.

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I wasn't writing as if I were copying from a textbook at all, and I used common abbreviations. I also used in_frame and out_frame at first before reducing them to if and of, which I figured was perfectly followable. The fact is there's a very limited number of ways to compactly represent mathematical writing, and I went with the standard way of expressing things, which I feel is a pretty intuitive way.

Shando is right in saying that there is not enough force to accelerate an object to the speed of light, though i don't think you mentioned (sorry if you did) that the reason for this is that when an object gains velocity it also gains mass, an almost unnoticable amount at low speeds, but when travelling close to the speed of light it gains a large amount of mass. As Force = mass times accelleration, the force must increase enormously to increase the accelleration further.

As for actuall time travel, as far as we know it is physically impossible to travel backwards through time, however, there was an experiment that involved travel forwards for the individuals involved. Two nuclear clocks (extremely accurate and will never slow down or speed up) were in New York, and both set to the exact same time. One was loaded onto a jumbo jet and flew to England, while the other stayed in America. When the clocks were compared afterwards it was found that the one that had been on the plane was a tiny amount behind the other. So the passengers on an airline are experiencing time quicker than those on the ground. It has also been theorised that astronauts are about 10 seconds younger than they would normally be after they come back from a space trip.

Shan'do, you need to also clarify what "imaginary" means, whether it's in respect to direction or anything else. To someone with no mathematical background, "imaginary" doesn't mean anything and is a difficult concept to comprehend.

I'm not going to argue why your post looked like it was copied from a text book, I'm just saying you have to be careful when you're posting on this topic on this type of forum.

-I think that timetravel is possible but no one can work out the formula for it. if we and make miniture black holes that last for about 3 seconds, i think that we could do it.

Past dangers
If you change the past just a little bit, you could change your whole future. Lets say if i left something like a car behind in the early ads, then i try to travel to the present time it could be totally different.

Future traveling
I don't think that it is a good idea of forward traveling because if someone is meant to die on a certain date in the future then you go back and save them. It might also change the future. Also if the time travel fell into the wrong hands then the world might be destoryed.

True paradox thories
I don't know what would happen but if a portal stays open you wouldn't want to let something happen with your planet because something bad could happen.

This is my opinion anyways. So believe what you want to believe in.

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Originally Posted by Microwave

As for actuall time travel, as far as we know it is physically impossible to travel backwards through time, however, there was an experiment that involved travel forwards for the individuals involved. Two nuclear clocks (extremely accurate and will never slow down or speed up) were in New York, and both set to the exact same time. One was loaded onto a jumbo jet and flew to England, while the other stayed in America. When the clocks were compared afterwards it was found that the one that had been on the plane was a tiny amount behind the other. So the passengers on an airline are experiencing time quicker than those on the ground. It has also been theorised that astronauts are about 10 seconds younger than they would normally be after they come back from a space trip.

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This isn't strictly time travel (at least in the classic sense). I'd say that time travel in the classic sense would involve a sort of teleportation from point A to point B. This experiment, however, does show the effects of time dilation in my post. People who travel at high speeds have time pass significantly more slowly for them. In that sense, if we just want the ability to survive until a very far point in the future, all that would have to happen is that we would have to put said person in some vehicle that moves at a speed very close to the speed of light. That person would have barely aged, even if thousands of years have passed. (The amount the time is slowed by is the lorentz factor that I discussed in my second post in this thread).

Getting back, on the other hand, would be a HUGE problem :).

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Originally Posted by M16

Shan'do, you need to also clarify what "imaginary" means, whether it's in respect to direction or anything else. To someone with no mathematical background, "imaginary" doesn't mean anything and is a difficult concept to comprehend.

I'm not going to argue why your post looked like it was copied from a text book, I'm just saying you have to be careful when you're posting on this topic on this type of forum.

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Any time you're discussing any sort of non-trivial topic, you need to make a base point of knowledge that you assume people will know. Otherwise, we could continue to make this argument back towards "you need to clarify what you mean by "addition"", but I'm pretty sure that'd be a waste of all of our time. In my case, I assumed some knowledge of complex numbers. In particular, because my post was directed at RagnaToad, I tried to estimate the level of mathematics I thought he would be comfortable with and started from there. Obviously, if people get confused at particular levels, I'd be perfectly happy to clarify if they just send me a private message or something, but I don't need to clarify anything. I'd expect people with no mathematical background probably would get lost far before I start talking about imaginary numbers . In the case of imaginary numbers, I'm simply meaning that the value of the time dilation is going to be imaginary, which mathematically means that the value is going to be some number multiplied by the square root of -1 (better known as i]). However, as I said in my post, that means that we really don't have any idea of what the time dilation effects would be at values greater than the speed of light. If we know that time is dilated by a value of 1/2, it means pretty clearly that someone will experience time passing twice as slowly as before. If we know that time is dilated by a value of 3i, it's far less clear what that means, as it is impossible to know which number is bigger out of, say, 3i and 3 (this is a proof that comes from the field of real analysis in mathematics, but it's definitely a discussion for another time, so just take my word for this.).

There was no way to answer his question without going into mathematical precision. Just because people make arguments using equations doesn't mean they're copying from a textbook ;).

First of all I would like to say that I pretty much believe that time travel will never exist. (well, not future travel). It just doesn't seem plausible to transport yourself to time that does not exist. The closest way of achieveing this would be to cryogenically freeze someone and thaw them out in the future, as Silver pointed out. Although it's not instantaneous, the human body would still be the same age in the future as when it was originally frozen.

As for time travel to the past, that seems like a more plausible idea. The past DOES exist. However, I don't believe that mankind will EVER achieve this accomplishment. Twould be kinda hard to roll back the clock when time is continuously ticking away.

I think the closest that mankind will ever come to being able to use time travel would be through the use of wormholes. To travel to a different point in existence and use no time to get there would be considered time travel, although you would be travelling through the present.

Science has proven that there is a direct correlation between velocity and time. The faster and object moves, the slower time seems to tick in relation. Humans would have to achieve hellacious speeds before they could even think about any form of time travel.

Time travel to the past could never happen, thats perfectly obvious. Thats my view, anyway. If it were ever possible then it would have already happened, surely? If somebody from the future hasn't already visited us then it will never be possible for us. of course, you could argue that they made themselves unknown, blended in even. That's a stupid assumption also in my oppinion..

EDIT: The above is just my view on time travel. My answer to the question is below.

If you truly think about it a change in time could never happen. No matter if a person came back from the year 5000 and shot somebody with a laser. You know why? Because that would be the norm. If you think of time in time-travelling terms then time is a loop. You can travel anywhere you want on this loop. That means that whatever could theoretically happen via the use of time-travel would have already happened. No matter which way you try to change a thing, it would have already happened.

Confused? Then I'll use the laser man again. Say he did shoot somebody. Well then that person died, yes? Then he was always going to die at that point in the time loop. And he always would, because thats the past. It couldn't affect the future because it has already happened and was always going to.

So, yes. Time travel without a paradox would be possible because changing what has already happened is impossible. It would happen no matter what, or it wouldn't have been so in the first place.

I hope I explained that properly. If not then BAH, it's a tough one to explain.

Hyz.

I don't see how time travel is possible, and to understand that, you have to understand that there is actually no such thing as time. We've invented the concept, very much the way we invented the idea of love. Love is a thought, but not a tangible, measurable, quantifyable property, and likewise time is an idea, an invented term to help us give meaning to an otherwise unexplainable concept. It helps us put order to a sequence of events, but just like love, there is in actuality, no such thing.

Another way to look at it would be to consider the concervation of matter, which of course says that matter can neither be lost or created. Pretend for a moment the past or future does exist, and you could get to it. In order to get there, you would have to somehow subtract your matter from the current time, and then add it to the time you arrive at. You can do neither by our current understanding of the laws of physics.

Well, I could just jump on the bandwagon and say it's impossible, but what fun is that? A "What if we could" is much more entertaining.

Ok, so assume at some point in time we DO find a way to go back in time.I personally think trying to change the past would be alot like the movie Deja Vu. The past has already occured. If someone from the future went back to yesterday, it already happened yesterday, we've already seen the changes caused by it. By going back in time to altar the past, you wouldn't be changing your future. You'd be causing your future. If i go back in time to try to stop something from happening, I will in fact cause it to happen. Because the point I went back to, already occured, if I will ever have a way to go back to it, I already did. If i tried to go back and make sure I was never born, we get the whole grandfather paradox going on. Then quantum theory suggests, one reality will go on where I chose not to kill my grandfather, one will go on where I did. Since I won't exist in the one where I did, I can't return to it to see a different present. So, as far as I'm concerned, the past is set in stone.

Given minimal thought, I would say the future can be changed, but then I consider my own theory on the past. I would in fact BE that past in relation to that future. So, if I chose to go to the future, and come back to fuc with it, that would change the fture, but I've already seen that future, and to that world, I am the past, so whatever I did, from the perspective of that future, I had already done. Long story short, if I go to the future, my present is the past. My previous theory states the past is unchangable, meaning my present is unchangable as well, because in relation to a future I've already seen, it IS the past. The most I could see happening is going back and creating another universe by making a change to the present. So I could possibly change MY future, but the future I went to would be unaffected.

All this of course is assuming time travel is possible, which at the moment, I do not believe. I believe that time is simply a unit of measurement created by man.

It's not possible, imo.

If it were, I don't think you can create a paradox. In fact, the first thing I'd do is go into the past and shoot myself in the face just to prove it. I wouldn't instantly die because the past I'm visiting would be a different past than mine. And in the future that corresponds to that past, I would not exist as I would in my future (even though technically I guess I wouldn't anyway, because I'd be gone and in some other past. Hmm.

But I don't know if that's true (how could I). I was under the impression that time and space are one and there is only one existence, the "now".

Though, haven't scientists witnessed particles "disappearing" and reappearing (which can't be possible due to Einstein's theory of matter)? They speculate that those particles are entering a different "dimension" or "universe" or something and interacting with stuff there, and then returning to ours. They exist in both places, though we cannot see the other for some reason.

This kind of stuff makes me wonder about ghosts, and our perception on where we are. I know our eyes can be easily tricked, and I'm wondering if maybe things just aren't how we believe them to be at all because we can't grasp the entire picture.

But that's a little off subject, so, yeah. I don't believe in paradoxes. Either time travel isn't real, or we're missing some calculations.

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Originally Posted by Microwave

Shando is right in saying that there is not enough force to accelerate an object to the speed of light, though i don't think you mentioned (sorry if you did) that the reason for this is that when an object gains velocity it also gains mass, an almost unnoticable amount at low speeds, but when travelling close to the speed of light it gains a large amount of mass. As Force = mass times accelleration, the force must increase enormously to increase the accelleration further.

As for actuall time travel, as far as we know it is physically impossible to travel backwards through time, however, there was an experiment that involved travel forwards for the individuals involved. Two nuclear clocks (extremely accurate and will never slow down or speed up) were in New York, and both set to the exact same time. One was loaded onto a jumbo jet and flew to England, while the other stayed in America. When the clocks were compared afterwards it was found that the one that had been on the plane was a tiny amount behind the other. So the passengers on an airline are experiencing time quicker than those on the ground. It has also been theorised that astronauts are about 10 seconds younger than they would normally be after they come back from a space trip.

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This isn't what most people consider time travel, this is something you can experience on a regular basis. This form of time dilation is a gravitational effect, nothing to do with the speed at which the measuring device travels. Both are functioning as intended, they're just too dumb to realize the effects of gravity on them relative to the clock on the ground. You're by no means traveling through time as both situations are occurring simultaneously.

I love the multiverse, somewhere out there im dictator of the world at the age of 25, or another one where i work at DC or Marvel comics, to time travel folds would have to be made in the 4th dimension, but even if you were to change the past all you would do is follow into the other universe where your changes happen, you would not cease to exist.