Time travel is not possible - would you agree?

[wazzuuup]

Hey everyone,

One standard definition of time travel is that of David Lewis's: an object time travels if the difference between its departure and arrival times in the surrounding world does not equal the duration of the journey undergone by the object.

I therefore believe that you can't travel in time without travelling in space. Wouldn't we therefore have to call it spacetime travel?

 

Please argue anything, I'm a fourteen year old girl working on a project. If I am wrong, I would please like to know!

[Uncle Martin]

From what I understand time travel is not ruled out by any physical laws. The energy requirements and mechanics of actually achieving it seems rather unlikely to me. Of course we are all tavelling through time as a default function, the real trick is to either accelerate or go in reverse. I wish you luck with your project,... could you tell us more about it specifically, that may help to steer the discussion in a more helpful direction.

[wazzuuup]

If one were travelling with one 'Earth second' per 'Earth second' in time on the planet Earth while going from point A to B, it is not 'time travel', because the difference between your time of departure and arrival times in the surrounding world equals the duration of the journey ondergone by the object.

[wazzuuup]

But, if you were to move at 99.9 % the speed of light for five years towarsd Alpha Centauri, and then come back again (taking another five years), 70 years would have elapsed on Earth. This would be calculated suing the equation

 

dt= 1 / ?(1-(v^2/c^2)) * dT

 

dt would be the coordinate time (earth time) and the dT would be proper time (travelling 10 years)

 

However, my argument is that you can't achieve any time dilation or other form of travelling in time where your time is different to the surrounding world's without travelling in space.

 

THus, we should call time travel space-time travel.

[wazzuuup]

* the ? stands for a square root in the above equation

[Freethinker]

Originally posted by: wazzuuup

* the ? stands for a square root in the above equation

 

Do you IRC?

[Freethinker]

Originally posted by: wazzuuup

THus, we should call time travel space-time travel.

 

I can't say I find anything specifically wrong with your construction nor assertion.

 

What I am wondering is, is this a etymological question more than a physics question?

 

Yes it would seem that it would be incorrect to refer to a timespace dilation effect as "time travel". In fact it would seem that it is not even correct to call it "space-time travel". Any time one person/ object is in motion compared to another they will have different "time dilation" components.

 

Further is the issue actually ONLY termonology given to "time variation" phenom thru relative motion? Or is it whether there is a more correctly termed "time travel" event which would create a timespace anomaly for an individual relative to the norm?

[wazzuuup]

Originally posted by: Freethinker

Originally posted by: wazzuuup

 

* the ? stands for a square root in the above equation

 

 

 

Do you IRC?

 

What would IRC mean? I'm sorry, but not everyone's first language is English.

When I copied and pasted that equation, it was a square root, but when I pasted it in the forum, it suddenly turned into a question mark.. the rest is self-explanatory.

 

But anyways, back to the topic. I didn't want to go into any etymology or termonology of the word 'time travel'. My apologies. I was just wondering if you could reverse or accelerate in time without moving. Theories about wormholes, superstrings, time warps, Godel's Universe etc. all include space.This is why I thought of naming it 'space-time travel'.

 

I agree that when one person/ object is in motion compared to another, they will have different "time dilation" components. But would this imply that every single moving object would time travel, despite the miniscule slow-down factor? And isn't everything moving?

[Freethinker]

Originally posted by: wazzuuup

What would IRC mean? I'm sorry, but not everyone's first language is English.

Actually IRC is not english specific, anymore than other termonology used on the net. IRC is Internet Relay Chat. You might say the original chat room, IM group or Blog. And still better.

* the ? stands for a square root in the above equation

If you make a mistake on a line of text you just sent, you correct it by starting the next line with an "*" followed by the correction, just as you did. So I thought I would ask.

 

More at

 

http://www.irc.org

But anyways, back to the topic. I didn't want to go into any etymology or termonology of the word 'time travel'. My apologies. I was just wondering if you could reverse or accelerate in time without moving.

OK, well there is a difference between asking IF and stating why. It seemed your first post was more stating why we couldn't and thus why we should change the name. That is why I wnet down the path I did.

I agree that when one person/ object is in motion compared to another, they will have different "time dilation" components. But would this imply that every single moving object would time travel,

When Time Travel is defined that way, then yes that would be correct. Everything moving in relatively different directions/ velocities/ .... each has it's unique GR timespace.

And isn't everything moving?

Or not?

[wazzuuup]

To Freethinker, thank you for all your replies, you've helped me improve my communication and thoughts. But the more I read on these forums, the more confuzed I get.

 

For example: on 07-08-2004, in the forum 'What will be the changes if we move from 3D to 4D', GAHD said, "Every experiment that has shown any dissonance in clock 'tics' can be disproven, or has had massive amounts of data doctored or just plain ignored (like the Hafele-Keating Experiment). NO ONE has been able to show time dilation occurs except with math (which then breaks down in real-world applications)."

 

This seems to contradict everything.

I do believe that time dilation has been applied to application. Muons are particles that are produced when cosmic-ray protons strike air molecules in the upper atmosphere of our planet. Normally (at rest), they persist for about two millionths of a second before decaying into energy and other, less massive plarticles; hence none of the muons should reach the ground. However, apparatus places at sea level and atop Mount Washington, New Hampshire, was ale to detect the fast-moving muons and to measure a significantly longer tifetime for them; relative to our fixed (Earth based) reference frame, their 'natural clocks' had apparently slowed down. In fact, while traveling at 99.4 percent of the velocity of light, muons endure for about sixteen microseconds, an eightfold increase in their usual lifetime. This time extension matches to within 1 percent that predicted by Einstein's theory of special relativity. (I got his information from a book "Relatively Speaking" by Eric Chaisson).

[Uncle Martin]

Wazzuuup,

You must remember that there are contrasting opinions posted here. Some totally reject time dilation as a real phenomenon, others accept the evidence and mathematical predictions. The muon experiments you reference are a good example of proof. I think what GAHD would like is an experiment with actual humans moving at relative velocities, which seems unlikely to happen anytime soon. My personal interpretation of the evidence leads me to accept time dilation as a real occurrence, even though the concept is counter-intuitive to me.

[wazzuuup]

I once read that time 'jumps', meaning it's discontinuous. It's difficult to imagine this, but it's just like a movie; when there are 24 or more images per second passing, we can't see these seperate pictures, so we get the impression that it flows. These seperate time units, time quanta, would be 0.5391 * 10^-43 seconds. The formula of the Planck time is:

 

T = (GH / c^5)1/2 (H=h/2pi)

 

I must admit I haven't particularly examined the wormhole or superstring theories for backwards time travel, but it seems illogical to me that you can reverse time which is made up of tiny units just following each other up. You can throw a rope, and pull it back because all the particles that make up the rope are connected. But time quanta isn't made up of anything, so the unit just ends after each Planck time.

 

Pretend you go back 30 years in time using any backward time travel theory, it would have taken time for you to do this (because you can't time travel without travelling in space, and thus travelling in space takes time). Thus I would like to hypothesize (without much support I admit) that you would still be older than when you decided to go back in time. If you reverse your movements, your time still ticks forwards.

 

Pretend I am wrong that reverse in time is impossible(which is very likely. I have never seen any proof that backwards time travel is impossible). If you really reversed the time, you would have to reverse your actions as well because the time quanta is stuck to the changes in space of that time interval. We ignore my thought that the time quanta from thirty years ago already 'stopped'. In this case, you would actually become younger, until you didn't exist anymore because you weren't born yet. This doesn't seem to make sense because your memory would have to shrink, etc.

 

If you actually 'saw' the original copy of yourself, this would again bring up the well known paradoxes people have mentioned. But because the 'future you' wasn't there in the original version of the past, some people came up with the idea that there exists parellel universe. To me, this seems very far fetched. How would you happen to land in this parellel universe?

 

While writing these paragraphs, I thought of something else. If we again assume it's true that time is discontinuous, this would mean that in the interval between two units of Planck times, there would be no time.

Only in this case of 'no time', would you be able to travel forwards or backwards. It would take 'no time' to travel from a 'no time interval' somewhere in the year 2004 to a 'no time interval' somewhere in 1500, or somewhere 400 years after the big bang (if there was a big bang). 'No time intervals' can't stop existing because they never existed.

But such an idea for travelling back in time has the problem that this would contradict my idea that you can't travel in time without travelling in space, because the 'no time intervals' can't allow any space travel (or any other change), or else you will land in the consecutive time unit again which is the time we only perceive. Thus again, it seems impossible to travel back in time.

[wazzuuup]

I hope you guys understand what I was trying to put foward (I'm not that strong in communication).

[Tormod]

Wazzuuup, I'm not sure where GAHD gets his ideas from (he's a cynicist at heart ) but I for one believe that time dilation is proven beyond doubt to happen. It might be a definition af terms since it is after all a matter of "time according to WHAT".

 

Yet time dilation is not, as I think FT points out above, the same as time travel.

 

Consider this: If you ask a person who has traveled near light speed for a year how long he has been gone, he might say "a few days". Yet we know he has traveled for a year (Earth time). He might only have aged a few days, too. So his biological clock has only gicked a few days while ours have ticked a full year. Yet he has not traveled in time. He is simply a "victim" of time dilation.

 

In Orson Scott Card's sci-fi book series about Ender (beginning with Ender's Game) people travel forward in time in exactly this way, by moving at speeds close to the speed of light. But they have no way to travel backwards in time (except for a completely fictional way late in the series - but even then they actually only travel _instantly_, ie without the passing of time, not actually to an earlier time).

 

Not sure if this is of any help but I wouldn't take any single post in these threads as evidence - you need a bigger picture. Then again, maybe GAHD can help us out here.

[Tormod]

Originally posted by: wazzuuup

...I would like to hypothesize (without much support I admit) that you would still be older than when you decided to go back in time. If you reverse your movements, your time still ticks forwards.

 

This is not a new hypothesis and I think also very logical. Moving back in time would not reverse your biological clock. So although things outside your spaceship would appear to move backwards in time, inside the spaceship they would not.

 

If we imagine a machine that does not need to move, but could place you anywhere at anytime, you would not necessarily age more than the time it took for the machine to relocate you, which might only be a few fractions of a second. But your biological clock would still tick forwards, yes.

 

If you really reversed the time, you would have to reverse your actions as well because the time quanta is stuck to the changes in space of that time interval. We ignore my thought that the time quanta from thirty years ago already 'stopped'. In this case, you would actually become younger, until you didn't exist anymore because you weren't born yet. This doesn't seem to make sense because your memory would have to shrink, etc.

 

No, you're right, it doesn't make sense. I think you are confusing the "continuous vs fractioned" time thoughts with what happens to physical objects moving through time. If time travel was (or is) possible I don't think it could possible work by flipping your biological clock, because that would be av iolation of the second law of thermodynamics, also known as "entropy", because it would mean that your closed system would get more and more ordered (you would get younger and smaller). Considering that you are inside a spaceship, for instance, how would you body "know" how to shrink back to it's previous states? You would not be in the surroundings that you were in when you grew up - so I think there is a big fallacy here.

 

Your idea that past time is "spent", ie can't be revisited, is interesting but there are other options. Goedel hypothesized that in a rotating universes you would have pockets of space where the arrow of time would move backwards. Say, if you managed to move against the rotation of space fast enough, you could also theoretically end up where you started before you left. Yet you would still be older, and you would see your old "you" leave. (Leaving out the paradoxes for now).

 

If you actually 'saw' the original copy of yourself, this would again bring up the well known paradoxes people have mentioned. But because the 'future you' wasn't there in the original version of the past, some people came up with the idea that there exists parellel universe. To me, this seems very far fetched. How would you happen to land in this parellel universe?

 

A very good question and the way it's phrased it demands the use of Occham's Razor: It's not possible.

 

While writing these paragraphs, I thought of something else. If we again assume it's true that time is discontinuous, this would mean that in the interval between two units of Planck times, there would be no time.

 

I think this depends on what we define "time" as. As far as I've understood it, the Planck time is the shortest possible *measurable* (theoretically) time span. Timespans shorter than this would have no meaning. Yet this is pure speculation. You couldn't possibly "end up" between two plank times because a planck time is a definition, not an actual event.

 

I commend you on your thought work here. I rarely see such well-formed ideas, based on a real quest for knowledge. Good work.

[wazzuuup]

Thanks Tormod (and Uncle Martin and FT!) for having helped me clear up my thoughts, especially the difference between time dilation and time travel had been troubling me.

[Freethinker]

Originally posted by: wazzuuup

To Freethinker, thank you for all your replies, you've helped me improve my communication and thoughts. But the more I read on these forums, the more confuzed I get.

Get used to it! :-)

 

That is the way reality works. The more you learn, the less you realize you know. And that is the most fun part. Each new bit of knowledge gives you that many more possible directions to learn more about. I pitty people that are locking into a defined limited knowlege base based on some antiquated set of doctrine.

For example: on 07-08-2004, in the forum 'What will be the changes if we move from 3D to 4D', GAHD said, "Every experiment that has shown any dissonance in clock 'tics' can be disproven, or has had massive amounts of data doctored or just plain ignored (like the Hafele-Keating Experiment). NO ONE has been able to show time dilation occurs except with math (which then breaks down in real-world applications)."

Yes the problem with the internet in general is trying to tell accurate info from the massive amounts of bad information out there. Anyone that wishes can publish anything they wish and you can stumble across it without benefit of prior knowledge of it's accuarcy.

 

Often information is structured in such a way as to make it seem more credible than it is. It always helps to include verifyable resources even if not correctly presented. For instance in the post you quote we are told

NO ONE has been able to show time dilation occurs except with math (which then breaks down in real-world applications).

This statement is quite clear. That in the real world,

NO ONE has been able to show time dilation occurs

no test ever anywhere at anytime....

 

Yet you mention one specific test that proves this wrong.

 

Further the original poster claims that we can just

plain ignored (like the Hafele-Keating Experiment)

how can he make this claim. I can only find one source to support any claim of Hafele and Keating Experiment being less than a perfect test of time dilation.

 

Further to claim there are no others is competely false.

 

"The Perihelion of Mercury. As you know, planets move in ellipses around the sun. However due to the influence of other planets their orbits are not quite closed; their perihelions (the line between the sun and the point of closest approach of the planet) will not be stationary in space but moved around the sun in a motion called precession. There is a contribution to this precession predicted by General Relativity. Mercury, the planet nearest the sun, should show this effect most of all, since it experiences the greatest gravitational effect. Indeed the Newtonian calculations of the perturbing effects of the other planets account for only 531 out of the observed 574 seconds of arc per century; General Relativity has to be invoked to explain the remaining 43 seconds."

http://www.upscale.utoronto.ca/PHY100F/relgen.htm

 

So yes, you must look closely at any and all claims. Consider the source and find valid outside support for anyhing before totally accepting it.

 

And the more you do this the more you will find how much more there is to know!.