Time Dilation = Time Travel? – I don’t think so.

[HighRiser]

Time dilation due to acceleration or suspended animation are the only theoretically feasible methods of time travel that have been thought up. Let's disregard suspended animation for the moment and focus on acceleration.

In the traveller's reference frame, the traveller moves forward in time at a rate of more than one second per second, as compared to the rate of the reference frame the traveller left. The traveller's wristwatch always appears to the traveller as functioning normally; one second per second, just as the non-traveler's watch appears to function normally to himself.

When the watches are compared after the traveller returns to the origin, though, they don't agree with each other. The accelerated watch will show fewer seconds elapsed. It seems reasonable to me to call this time travel.

If I understand ynot correctly, (s)he considers this form of time travel to be inaccurately described as such, because time actually, perceptually, passed for each party involved. What ynot wants to call time travel would be some as-yet undescribed method in which the traveller pops out of existence today and pops back into existence last (or next) Tuesday, without the traveller perceiving any motion or time passing.

This seems to me to be a purely semantic discussion, but I am, by my own admission; an idiot.

 

[HighRiser]

The little club comprising authors of dead theories from past centuries has more than one member, i.e. it' not just Chuck Darwin, Albert Einstein is a member of that club as well. There is no physical basis for time travel.

Welcome to the forum!

What the hell are you talking about?

 

[Roboramma]

Say you're travelling in a car from New York to LA. Your friend is in another car going to the same place. Oddly both cars have carbon monoxide leaks, and the amount of carbon monoxide getting into the car is proportionate to the distance it travels. If the car stops, you feel no ill-effects (weird, right?), but as the car covers more distance, the amount of carbon monoxide increases, and when it reaches a certain threshold, you will die. This is true of both you and your friend.

You discover this, but don't want to stop for repairs. However, you realise that if you follow your original route, you'll be dead before you get to LA!

You have a map, and you find a different, more direct route from New York to LA (originally you were planning to go north through canada, drive the trans-canada highway to Vancouver and then drive south the LA). Following this route you will survive to see LA. You tell your friend about this, but he wants to enjoy the drive through Canada.

So you go your separate ways and you get to see LA before you die (while your friend is still on the road).

Now, it's not your choice of a different route that determines the fact that you were travelling through space. But your choice of a different route allowed you to arrive in LA before you died. This is very much the same as time dilation, which can be seen as simply taking a different route through space-time, one in which you need cover less time to get from event A in space-time to event B in space-time.

 

[Brian-M]

If you truly travelled in time you wouldn’t exist in the departure/arrival time frame for the 100 years of your time travel.

Is there such a thing as a "no true Scotsman time traveler" fallacy?

I'm a time traveler. I'm currently traveling forward in time at approximately 1 second per second relative to Earth.

 

[surreptitious57]

Formula For Calculating Time Dilation Relative To Light Speed


Take Speed : Divide By Light Speed : Square It :

Subtract From One : Take Square Root


Example : Calculating Time Dilation Of Body Travelling At 240 000

Kilometres Per Hour For One Hour


240 000 / 299 792 = 0 . 800555

0 . 800555 x 0 . 800555 = 0 . 6408883

1 - 0 . 6408883 = 0 . 3591117

0 . 3591117 = 0 . 5992592 x 0 . 5992592

0 . 5992592 x 60 = 35 . 599992

35 . 599992 = 35 Minutes 57 Seconds


[ About Time : Einsteins Unfinished Revolution : Paul Davies ]

 

[Pup]

If you truly travelled in time you wouldn’t exist in the departure/arrival time frame for the 100 years of your time travel. You would skip 100 years. If you were merely in suspended animation however you would exist in that time frame for the full 100 years. Pretty much what Toontown said . . .

Since the popular understanding of "time travel" is a fictional concept, I don't see how one can get away from defining it by its fictional origins. As I mentioned earlier, the original "time traveller" in H. G. Wells' story appears to travel through time by existing but going faster than everyone else's time. He sees day turn to night in a second, for example, while everyone else sees it at normal speed, and then gradually accelerates so day and night blend together in grayness. However, he considers his existence attenuated and less solid while he's traveling faster than others, and is apparently invisible to them, although he can see the outer world like a speeded up movie.

The whole concept is fraught with practical difficulties, such as what are you remaining relative to, in space? Wells' time traveler apparently remains stationary relative to the actual spot on the surface of the earth where he began, for example, and that premise is usually repeated in other time travel stories.

The fact that Wells' imaginary concept is still commonly used today shows the iconic nature of his story. I don't think that one can really redefine "time travel" in a way that excludes his story and all the derivative versions of his concept. Well, I mean, you could, but it would be changing the meaning of a well-established premise.

 

[ynot]

Time dilation due to acceleration or suspended animation are the only theoretically feasible methods of time travel that have been thought up. Let's disregard suspended animation for the moment and focus on acceleration.

To my mind time dilation would essentially be a form of suspended animation so I don’t see any difference in using either method or both. As there are real-life examples of suspended animation, and it’s an easier concept to understand than time dilation, I thought it would be easier to explain why suspended animation isn’t time travel and therefore neither is time dilation. Don’t seem to have been able to changes anyone’s mind so far however.
I don’t have time to continue right now but will time travel to a time when I do at some later time

 

[Reactor drone]

Earth time is the standard against which possible time travel is being measured and is the time that it's being claimed is being traveled to the future of. The person travelled for 100 years of Earth time and rejoined Earth time after 100 years of Earth time. The traveller never travelled ahead of Earth time in any time. A period of dilated time suspended animation compared to Earth animation.

By this standard no method of time travel would be considered time travel. If I step into a mythical time travel device, say a Tardis, and set the co-ordinates for 100 years in the future then 100 years will have passed normally on Earth while I'm inside the ship therefore no time travel will have taken place from the non-time traveller's perspective.

 

[Roboramma]

To my mind time dilation would essentially be a form of suspended animation so I don’t see any difference in using either method or both. As there are real-life examples of suspended animation, and it’s an easier concept to understand than time dilation, I thought it would be easier to explain why suspended animation isn’t time travel and therefore neither is time dilation. Don’t seem to have been able to changes anyone’s mind so far however.
I don’t have time to continue right now but will time travel to a time when I do at some later time

There is a difference between time dilation and suspended animation: under time dilation all processes will recored less elapsed time. That's not the case with suspended animation.

Also, if you look at the world-line of an object that travels away from the earth and then back to it, you'll find that it's time component (the proper time) is shorter than that of the world line of an object that stays on the earth.

Similarly if you and I start off on a race and you walk but I run to our destination, I'll get there first, but we will both have crossed the same distance. However, if instead we both ran but I found a short-cut, I'd still arrive first, but I'd have done it by crossing a shorter distance. Those two races both have the same outcome, but they are very different.

 

[Brian-M]

There is a difference between time dilation and suspended animation: under time dilation all processes will recored less elapsed time. That's not the case with suspended animation.

Yep, in theory you could tell the difference between a cryonic suspended animation time traveler and relativistic time dilation time traveler by carbondating a hair sample.

(In practice, you can tell the difference by looking because one is dead from ruptured cells due to the freezing process and the other is dead from being splattered across the spaceship floor due to the huge accelerations needed to reach the velocities needed for significant time dilation to occur.)

 

[ctamblyn]

Yep, in theory you could tell the difference between a cryonic suspended animation time traveler and relativistic time dilation time traveler by carbondating a hair sample.

(In practice, you can tell the difference by looking because one is dead from ruptured cells due to the freezing process and the other is dead from being splattered across the spaceship floor due to the huge accelerations needed to reach the velocities needed for significant time dilation to occur.)

It depends on how long you're willing to travel. Suppose Alice departs from Earth and undergoes acceleration of constant magnitude g (as judged by her) while Bob stays at home on Earth. At the end of some period of time t_B (as judged by Bob), Alice's path brings her back to Earth and she compares clocks with Bob. You'd find that Alice had aged by an amount

t_A = (c/g) sinh^-1(gt_B/c)
​

If Alice were subjected to a reasonably gentle acceleration of 9.8 m/s² for 1 week in Bob's frame, she would age by about 40 seconds less than 1 week. If the trip lasted as long as a year from Bob's viewpoint, Alice would experience only 1 year minus 45 days. A journey time of 8 years according to Bob (about enough time for Alice to get to Proxima Centauri and back, without stopping for souvenirs) only takes 3 years as judged by Alice.

More info: Hyperbolic motion (relativity), Time dilation at constant acceleration

 

[Reality Check]

I don’t understand why it’s claimed that time dilation would equate to a form of time travel. ...

Well, ynot, I cannot understand why you do not back up this claim with links to the actual claim. Though I suspect that some ignorant person somewhere on the Internet thinks this !

Time dilation means that an observer looking at a clock that is traveling at different speed from them will measure that clock ticking at a different rate. It is not time travel in the usual sense (someone travelling into the past or future). It is a different rate of time passing.

The twin paradox has nothing to do with time travel. It is just that time dilation for the travelling twin means that they age less than the twin at home.

 

[Reality Check]

To my mind time dilation would essentially be a form of suspended animation ...

It is not that clocks stop, ynot. It is that clocks tick slower.
Suspended animation is for living beings. The classical muon experiment that shows fast muons have a longer half-life than slow muons does not any suspended animation.

 

[ynot]

Well, ynot, I cannot understand why you do not back up this claim with links to the actual claim. Though I suspect that some ignorant person somewhere on the Internet thinks this !

Time dilation means that an observer looking at a clock that is traveling at different speed from them will measure that clock ticking at a different rate. It is not time travel in the usual sense (someone travelling into the past or future). It is a different rate of time passing.

The twin paradox has nothing to do with time travel. It is just that time dilation for the travelling twin means that they age less than the twin at home.

I'm pretty sure most time dilation articles I've read mention time travel at least once.

Not only do many other forum members claim time dilation is time travel but some also claim that normal time passing is also time travel. Did you bother to read the thread?

So can I assume you agree that that time dilation isn't time travel?

 

[ynot]

It is not that clocks stop, ynot. It is that clocks tick slower.
Suspended animation is for living beings. The classical muon experiment that shows fast muons have a longer half-life than slow muons does not any suspended animation.

Suspending animation as I meant it doesn’t have to mean completely stopping life. It can also mean slowing actions down down. Chemical reactions can be slowed by lowering temperature. The decay of dead fruit can be slowed in a fridge. Perhaps I should've said "slowing animation". Theoretically travelling at the speed of light would completely stop clocks/time.

 

[Reality Check]

Suspending animation as I meant it ...

The fact remains that muons are not living things, ynot !
Muons do not undergo chemical reactions.
It is thus ridiculous to describe the time dilation of muons (and other nuclear particles) as "suspended animation", "slowing animation" or whatever term you come up with next to ignore the actual science of time dilation.

 

[Reality Check]

I'm pretty sure most time dilation articles I've read mention time travel at least once.

Well I am pretty sure most time dilation articles I've read do not mention time travel at all. However I tend to read articles about science, not science fiction !
I am pretty sure that no time dilation article that I've read has stated that time dilation is time travel.
I am totally sure that one time travel article I have read has a (fairly irrelevant) section on time dilation in it.

 

[ynot]

Well I am pretty sure most time dilation articles I've read do not mention time travel at all. However I tend to read articles about science, not science fiction !
I am pretty sure that no time dilation article that I've read has stated that time dilation is time travel.
I am totally sure that one time travel article I have read has a (fairly irrelevant) section on time dilation in it.

True - It's most articles I've read on time travel that mention time dilation, not the other way around. My bad.

But didn’t Stephen Hawking have to buy someone a copy of Playboy because time dilation proved the possibility of time travel? (perhaps I got that the wrong way around as well)

 

[ctamblyn]

True - It's most articles I've read on time travel that mention time dilation, not the other way around. My bad.

But didn’t Stephen Hawking have to buy someone a copy of Playboy because time dilation proved the possibility of time travel? (perhaps I got that the wrong way around as well)

Almost - it was a bet about the existence of black holes with Kip Thorne:

I have done a lot of work on black holes, and it would all be wasted if it turned out that black holes do not exist. But in that case, I would have the consolation of winning my bet, which would win me four years of the magazine Private Eye. If black holes do exist, Kip will get one year of Penthouse.

 

[ynot]

Almost - it was a bet about the existence of black holes with Kip Thorne:

Seems to be at least time travel related - http://plus.maths.org/content/time-travel-allowed

Also mentions the twins paradox in relation to time travel.