Reality Check
Penultimate Amazing
Mentions it in the trivial sense of traveling forward in time, the Earth twin moves forward at 1 second per second, the traveling twin a bit slower.
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Time Dilation = Time Travel? – I don’t think so.
- Thread starter ynot
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- time dilation time travel
Yeah. No one said anything about travelling backward in time.
This thread is really just semantics. If ynot wants to define time travel in such a way that time dilation isn't time travel that's fine. If someone else wants to define it in such a way that it is, that's cool too.
I really don't see the point of the whole discussion. Yet somehow I keep clicking on this thread...
So how do you define time travel?
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Yeah. Slower time would put you backward of normal present time but some are saying it's travel to the future.
Reality Check
Penultimate Amazing
ynot: it is up to the person who makes an assertion to support it with evidence - including defining what the assertion is!
This is your thread. It is your assertion. It is up to you to define time dilation and time travel.
theprestige
Penultimate Amazing
Fixed your quotes. You're welcome.
Anyway, I define time travel in one of two ways, depending on my context:
The physical way: Time travel is experiencing the passage of time at n seconds per second, relative to some other frame of reference. This can produce some interesting effects, at least in theory. For example, traveling more quickly relative to someone in another frame, and thus aging more slowly than them.
The fictional way: Time travel is a narrative device by which characters are transported to a different time in the service of a story the author is trying to tell.
The physical way--time dilation--is very real, and is observed to happen all the time (so to speak). Whether or not to call it "time travel" purely a matter of personal preference. Objecting to calling it time travel amounts to little more than a curmudgeonly semantic quibble.
Out of curiosity, what would you say is the most notable article that you have read in the past three years, that conflates time dilation with time travel?
psionl0
Skeptical about skeptics
I know what you mean. It's like saying that you don't travel from A to B unless you are using a motorized conveyance. So walking from A to B doesn't count as travel.This thread is really just semantics. If ynot wants to define time travel in such a way that time dilation isn't time travel that's fine. If someone else wants to define it in such a way that it is, that's cool too.
I really don't see the point of the whole discussion. Yet somehow I keep clicking on this thread...
The problem with restricting the definition of "time travel" is that then you need a new generic term to describe moving to a point in the future by any means that is farther (in time) away than you would get just from natural aging.
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If being in a time younger than you normally would be is travelling into the future then is being in a time older than you normally would be travelling into the past? As in this scenario . . .
ETA - This might be clearer (or not) . . .
In “normal time” everything happens at the same rate.
In “dilated time” everything happens at the same rate but at a slower rate than normal time.
A clock travelling from “normal time” to “dilated time” then back to “normal time” will show an earlier time than a clock that has remained in “normal time”.
A clock that travels from “normal time” to “dilated time” after another clock has travelled from “normal time” to “dilated time” will show a time later than that clock.
Of not, why not?
ETA - This might be clearer (or not) . . .
In “normal time” everything happens at the same rate.
In “dilated time” everything happens at the same rate but at a slower rate than normal time.
A clock travelling from “normal time” to “dilated time” then back to “normal time” will show an earlier time than a clock that has remained in “normal time”.
A clock that travels from “normal time” to “dilated time” after another clock has travelled from “normal time” to “dilated time” will show a time later than that clock.
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It seems pretty simple to me. There are two events in space-time A and B. Any object that is present at both events must necessarily have travelled between them.
Thus, we are all travelling through time. Time dilation is a means of taking a short-cut through time such that the proper time between A and B is less than for non-dilated travellers.
Thus, we are all travelling through time. Time dilation is a means of taking a short-cut through time such that the proper time between A and B is less than for non-dilated travellers.
How do you define what "proper time" is?
No, it's also travelling into the future. Just taking more time to do so. It's clearly not travelling into the past, as you can see by looking at the date when you arrive. Hint, if the numbers go up (2013,2014,2015) then you are travelling into the future.
But 2014 in "normal time" could still be 2013 in "dilated time" according to the clock that entered "dilated time" before the other clock.
The first clock to enter "dilated time" says it's 2013 but the second clock to enter says it's 2014, and they're both in the same reference frame.
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theprestige
Penultimate Amazing
Proper timeWP is a technical term. It is defined as "the elapsed time between two events as measured by a clock that passes through both events".
Okay, you start with two clocks. They both read september 25 2013. Is it possible for the clocks to separate and then come back together and one of the clocks to read some time before september 25 2013?
Any time after september 25 2013 is in the future of september 25 2013. If both clocks, A and B, start at september 25 2013, regardless of how much time passes on B's clock, as long as A's clock reads some time after september 25 2013, it is in the future of september 25 2013.
Similarly imagine that I am walking north on a road and you are driving north on the same road. Shortly after passing me you take a diversion east for a long way. After some time and meandering you return north-west and meet me on the same road that I've been travelling all this time. No matter how many miles you travel on your meanderings, as long as I keep travelling north when we meet again we will still be north of our initial point of separation. And as long as you keep traveling north you will never be south of our initial point of separation.
No, but that has nothing to do with the scenario I outlined.
Clocks A and B are in “normal time” and both read September 25 2013.
Clock A travels to “dilated time” and runs slower than clock B.
When clock B ticks over to September 26 2013 clock A still reads September 25 2013.
So “normal time” is September 26 2013 and "dilated time" is September 25 2013.
If clock B then also enters “dilated time” (together again with clock A) it has gone from September 26 2013 back to September 25 2013 (even though it reads September 26 2013).
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So the selection of any particular proper time as opposed to any other is completely arbitrary?
I don't know what it means to "enter" dilated time. They both (clock A and clock B) arrive at the same point in space time having traversed different amounts of proper time in order to get there. However, there is no section on the worldline of either clock for which the proper time is negative.
I think I finally understand what you are saying: you have two clocks, one reads september 25, the other 26. We say that the one that reads 25 has travelled into the future by virtue of reading 25 while encountering a world in which clocks agree that it's actually 26. But it's equally valid to say that those other clocks have travelled to the past by virtue of reading 26 when encountering a clock that reads 25.
But here's the thing: That's not what I'm saying. I, at least, am saying that everyone is travelling forward in time. You can see this easily with a space-time diagram. The amount of time that different people experience between space-time events can vary. That's it. Moreover, september 25 on clock A is not necessarily in the past of september 26 on clock B. In fact, in this scenario they are in each other's present. However, september 24 on clock A certainly is in the past of september 25 on clock B.
Some people say we are travelling forward in time at one second/second. That's of course, a relative statement. Relative to a clock somewhere (anywhere) on earth I am moving forward through time at one second (on my clock)/second (on that other clock). If I were to go away from the earth and come back, I could look at my journey and find that I had, over that time, travelled forward at an average of 1/10th second(on my clock)/second(on an earth based clock). Someone on earth could, during that same period, say that, relative to my clock, they travelled forward in time at a rate of 10 seconds (on their clock)/second (on my clock). At no point will either of us have a negative reading.
Proper time is the time that a particular clock will read. If two spaceships drift past each other, their clocks will record different amounts of proper time. But you can use either one to set up a coordinate system, and all predictions calculated in one will agree with those made in the other.
Perhaps I should have said A zips around in a spacecraft then after a period of time dilation B also enters the same craft.
That’s exactly what I’m saying
Sure, but I was only talking about what I was saying. Possibly nit-picking but I don’t accept that being in an ever changing present is to be “travelling forward in time”. Constantly being in the present isn’t travelling through time as far as I’m concerned. (tomorrow never comes). I would say its experiencing time at a “normal” rate. To travel through time would be to experience time at an “abnormal rate”. Did I just say that time dilation would be time travel?
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