psionl0
Skeptical about skeptics
Regardless of whether the reference frame is A or B, neither clock is running backwards so there is no traveling to the past.
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Time Dilation = Time Travel? – I don’t think so.
- Thread starter ynot
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- time dilation time travel
Regardless of whether the reference frame is A or B, neither clock is running backwards so there is no traveling to the past.
theprestige
Penultimate Amazing
Not really. But proper time between events will differ between two observers traveling at different speeds. The important thing is to make sure you know which observer you're considering, and to make sure you always use that observer's clock to determine elapsed (or proper) time between that observer's events.
If you accidentally start mixing up clocks and events between different observers, you'll end up with absurd, meaningless results.
But note that different proper time measured by different observers is neither absurd nor meaningless; it is a physical fact.
theprestige
Penultimate Amazing
There's no such thing as a "normal" rate of time. Elapsed time is relative to an observer. Observers in different reference frames will each measure different amounts of elapsed time relative to each other. Observers one reference froam will measure different amounts of time dilation when considering observers in other reference frames. There is nothing special about your reference frame that makes your proper time the "normal" rate of time. An observer in a weaker gravity field would measure an equally valid proper time for themselves, and would measure time dilation in your reference frame. Which observer is measuring "normal" time?
Brian-M
Daydreamer
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(I know that this question isn't directed at me, but....)
I think it doesn't matter which measure of time is chosen. As long as all parties agree to go by time measurements from the same inertial/gravitational frame of reference it doesn't make any difference which inertial/gravitational frame of reference is chosen.
"Proper time" would be time as measured within whichever inertial/gravitational frame of reference is agreed on.
theprestige
Penultimate Amazing
"Proper time" actually has a specific technical definition in this context: The elapsed time between two events as measured by a clock that passes through both events.
Different observers in different reference frames may agree to all use the same frame and the same clock to produce a "common time" they all agree on. But this is different from the proper time for each observer.
But as one clock is running slower it’s time is backward of the other.
It’s claimed that a clock that’s backward (dilated) is time travelling to the future when it visits a time that’s ahead of it.
So why isn’t a clock that visits time that’s backward (dilated) not travelling to the past?
I think I and others explained this pretty clearly. I'll try again:
Let's say I want to see what the earth will be like in 2050. With the right technology, I could use time dilation to do so.
How would you propose to use time dilation to visit the past?
surrogate
Muse
It is still traveling into the future of the initial reference clock.
psionl0
Skeptical about skeptics
That's just silly semantics. If A's clock moves forward 1 week and B's clock moves forward 100 years then that's both clocks moving forward. Neither has run backward. It is not possible for B to move to a time prior to A's initial time when the travel started.
sol invictus
Philosopher
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Imagine a civilization of fish living in a big river. It's flowing pretty fast and the fish swim very slowly, so no one can swim upstream. But they can imagine it - they can imagine re-visiting parts of the river upstream of them where their ancestors lived, and such stories often appear in their fiction. They also imagine suddenly jumping downstream to the parts of the river their children will see, but that seems equally impossible.
Then one day a brilliant fishicist discovers that the river actually snakes back and forth, and that there are fast moving shortcut streams that cut off the bends, so you can swim through one and get much further downstream than would normally be possible in a fish's short life.
That's not a perfect analogy, but it's pretty close - and surely you agree that the discovery or traversal of such shortcut streams doesn't in any way, shape, or form constitute upstream travel?
To be a more valid “twins” analogy the shortcut would run slower than the main river and it would somehow slow down the aging of fish swimming through it. Twin fish would be swimming together at the entry of the shortcut and together again at the exit, and the fish that swam through the shortcut would be younger than the other at the exit. The shortcut fish doesn’t get further down the river quicker it gets there younger. In the time dilated human twins scenario one twin doesn’t end up “further down the river” than the other when they are back in the same time frame. They are in the same place and time (river) and one is younger than the other.
I’m not proposing the “back in time” twins dilation scenario because I think it makes sense or would actually be travelling back in time. Quite the opposite in fact. I’ve more been proposing that if one scenario isn’t valid then neither is its equal and opposite. Like all debates about time it always seems to come down to how you choose to define what time is and in this case what time travel would be.
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No, then it wouldn't be a valid analogy anymore.
The analogy as Sol presented it is very close. As you are presenting it, it no longer makes any sense.
Perhaps you could address it as presented?
Wait, are you disputing the validity of time dilation as a real phenomenon? Or are you still just talking about semantics ("it's not time travel")?
To me Sol’s analogy conflates distance with time and doesn’t replicate the circumstances of time dilation.
Given this thread is about whether or not time dilation = time travel it must be assumed for the sake of the argument if nothing else that time dilation is at least possible. I haven’t argued that time dilation isn’t time travel because time dilation isn’t possible. My purpose is to argue that time dilation isn’t time travel and I don’t see that how the time dilation may be achieved is important. If we say that one twin enters a magic room that causes time dilation and slower aging then that’s fine by me.
So one twin enters the magic room and ages at half the rate of the other twin. When the twin leaves the magic room s/he is half the age of the other and they then continue aging at the same rate. I don’t see any time travel
Regarding the hilighted part: yes, that's the analogy.
Where's the dilation in Sol's analogy?
The shorter path equates to the shorter time experienced in time-dilation.
If you look at it from the perspective of space-time, time dilation really is simply taking a path through spacetime whose time-component is shorter, in the same way that in Sol's analogy taking the shortcut stream is taking a path whose distance on, say, the x axis is shorter. It's possible that distance covered on the y-axis may not change at all. But the total distance will be shorter. The distance is shorter in almost exactly the same way that the elapsed time is shorter for a time dilated traveller.
psionl0
Skeptical about skeptics
How about, time dilation is not identical to being teleported into the future using a Star Trek transporter?