The Twin Paradox & Frame of Reference

[Delta1212]

From no point of view will any clock appear to run backwards.

Edited July 4, 2016 by Delta1212

[swansont]

Consider what happens to a clock very very far away from the accelerating rocket

The further away the clock is the more out of sync it becomes

 

 

You claimed that clocks would run backwards. Either show the math, link to an example showing exactly that, or retract the claim. "out of sync" does not mean "run backwards"

[granpa]

If the calculated time at Andromeda jumps forward a full day when I start moving that it obviously jumps back a full day when I stop.

 

Here:

You should see a rocket this time.

If not then maybe reload or bypass cache.

 

Edited July 5, 2016 by granpa

[swansont]

If the calculated time at Andromeda jumps forward a full day when I start moving that it obviously jumps back a full day when I stop.

 

Here:

You should see a rocket this time.

If not then maybe reload or bypass cache.

 

 

 

It's not obvious to me (it's obviously wrong to me), and you can't simply state something like this without proper support. Simply repeating it doesn't suffice. Clocks don't run backwards, and signals from clocks don't change order (they all move at c). Having a clock running faster than another doesn't mean a clock is running backwards. It's running forwards at a slower rate.

 

So let's see your analysis, or someone else's that you can link to. Where did that infographic come from, anyway?

[granpa]

are you saying the clocks wont be out of synch from the point of view of the rocket???

 

https://en.wikipedia.org/wiki/Relativity_of_simultaneity

Edited July 5, 2016 by granpa

[Strange]

are you saying the clocks wont be out of synch from the point of view of the rocket???

 

No one is saying that.

 

But clocks do not go backwards.

[swansont]

are you saying the clocks wont be out of synch from the point of view of the rocket???

 

 

No, I said nothing of the sort. One clock running faster than another directly implies they will be out of synch, since synchronization requires the same rate.

 

All I said is that I see no way for a clock to run backwards. Why won't you present any analysis that shows this, as you are apparently so convinced it's true?

[granpa]

You accept that they're out of sync and that the further away they are from the rocket the more out of sync they are.

Do you accept that my calculation of the time on a clock in Andromeda can become a full day out of sync if I start moving fast enough in the right direction?

What do you think happens when I stop moving?

Edited July 5, 2016 by granpa

[swansont]

You accept that they're out of sync and that the further away they are from the rocket the more out of sync they are.

Sure.

 

Do you accept that my calculation of the time on a clock in Andromeda can become a full day out of sync if I start moving fast enough in the right direction?

That's entirely plausible.

 

What do you think happens when I stop moving?

The rates (frequencies) equalize, but not the accumulated phase (time)

 

What doesn't happen is they make a sudden phase jump when one clock stops moving.

[granpa]

If I'm not moving my calculation of the time on a clock in Andromeda is simply the current time.

 

If I start moving at the necessary speed in the right direction than my calculation of the time on a clock in Andromeda jumps forward one day.

 

now I stop moving. What is my calculation of the time on the clock in Andromeda?

[Strange]

now I stop moving. What is my calculation of the time on the clock in Andromeda?

 

Why don't you show us what your calculation is, rather than asking us to guess.

[swansont]

If I'm not moving my calculation of the time on a clock in Andromeda is simply the current time.

 

If I start moving at the necessary speed in the right direction than my calculation of the time on a clock in Andromeda jumps forward one day.

 

now I stop moving. What is my calculation of the time on the clock in Andromeda?

"can become a full day out of sync" is not the same as "jumps forward one day" And your previous example is of a person already moving at v compared to a person at rest, which is not the same scenario.

 

But, if your clock becomes a day out of sync with the Andromeda clock, it will remain so when you stop moving. It will become more out of sync the longer you move.

[Eise]

Where did that infographic come from, anyway?

 

He made it himself, and put it on Wikimedia. No Wikipedia article references it.

 

See here.

Edited July 5, 2016 by Eise

[granpa]

A long line of stationary clocks stretches from here to Andromeda. I am stationary. All of the clocks are perfectly in sync with one another.

 

I begin moving toward Andromeda and now the line of Clocks all are ticking slower by a factor of gamma. So I deliberately slow my own onboard clocks down to match this speed.

 

 

The clocks also appear to be out of sync with each other. The farther away the clock is the more out of sync it is. The clock at Andromeda is a full day out of sync. But every clock that I pass agrees with my own clock at the moment when it passes by my rocket.

 

I now stop the rocket and return my onboard clock to normal speed.

 

The Clocks no longer seem out of sync with one another and agree with my own onboard clock

 

My calculation of the time on the clock at Andromeda is no longer a full day out of sync

 

All of this takes place in only a few minutes as measured by the stationary clocks

Edited July 5, 2016 by granpa

[Endy0816]

The passage of time itself wouldn't be impacted though.

[granpa]

From the Rockets point of view the clock at Andromeda went from being perfectly in sync with its own onboard clock to being a full day out of sync and then went back to being perfectly in sync again. Obviously at some point in that process it had to seem to run backwards from the point of view of the rocket

[Strange]

I now stop the rocket and return my onboard clock to normal speed.

 

The Clocks no longer seem out of sync with one another and agree with my own onboard clock

 

My calculation of the time on the clock at Andromeda is no longer a full day out of sync

 

That is wrong, surely?

[granpa]

I made one small error. Even though the line of clocks appears to be length contracted and and the clocks appear to be ticking slower they are so out of sync that the clock on board the rocket would actually have to be sped up not slowed down.

 

This is easy to see if you just look at it from the point of view of the stationary clocks

 

Nevertheless that doesn't change anything. The point is the rocket can adjust the speed of the onboard clock so that it's always in sync with whatever clock the rocket is passing.

Edited July 5, 2016 by granpa

[swansont]

A long line of stationary clocks stretches from here to Andromeda. I am stationary. All of the clocks are perfectly in sync with one another.

 

I begin moving toward Andromeda and now the line of Clocks all are ticking slower by a factor of gamma. So I deliberately slow my own onboard clocks down to match this speed.

 

The clocks also appear to be out of sync with each other. The farther away the clock is the more out of sync it is. The clock at Andromeda is a full day out of sync. But every clock that I pass agrees with my own clock at the moment when it passes by my rocket.

 

(noting that this deliberate change in the onboard clock is a change in the original scenario)

 

Show that this bolded part is true.

[MigL]

The rocket moves by a stationary ( wrt the rocket ) clock, and the onboard clock shows the same time as the stationary clock, say 12:00.

The rocket rider waits 24 hrs and checks again ( using a telescope of course ) and notices the stationary clock is only showing 11:00.

Since the rocket rider's subjective time hasn't slowed and seems to be running normally ( to him ), it APPEARS the stationary clock has jumped back one hour.

IT HAS NOT !

It has simply moved slower ( as measured from the rocket's frame ) such that only 23 hrs have elapsed in ( the rocket frame's ) 24 hrs.

No clock will ever actually move backwards.

( I think even grampa's own graphic uses the wording 'appears to' )

[granpa]

(noting that this deliberate change in the onboard clock is a change in the original scenario)

 

Show that this bolded part is true.

It's easy to see if you look at it from the point of view of the stationary clocks

[swansont]

It's easy to see if you look at it from the point of view of the stationary clocks

 

No, that doesn't work. The time difference depends on distance.

 

[math]t'=\gamma(t-vx/c^2)[/math]

IOW, the amount of error you get between the clocks isn't fixed. You already acknowledge this when you observe that the clocks that are further away are more out of sync. So resetting your clock to an adjacent one doesn't solve the problem you think you are solving. It will still differ with a clock that is far away, even if you adjust the rate.

Example: the clock at Andromeda is a day off. But the clock next to you agrees on the time. Somewhere along the path, there is a clock that is 1/4 of a day off, one that is half a day, one that is 3/4 of a day. If you reset your clock to any one of those, even if it is now running at the adjusted rate, it will not agree with the Andromeda clock when you get to your destination.

[MigL]

And of course, in the example you use, if the on-board clock is adjusted forward to be equivalent to each clock you pass, then each clock you previously passed and 'syncd' to would have been put back.

How is this relevant to your argument ?

As swansont notes, you're changing the parameters to give the ( apparent ) desired result.

 

If you continuously monitor both the on-board clock and the other frame's clock, you will only ever see the other frame's clock moving slower, such that it's continuously lagging ( wrt the on-board clock ).

If you observe at intervals, you will see the other frame's clock losing more and more time ( WRT the on-board clock ), giving the APPEARANCE that its running backwards.

[swansont]

The rocket moves by a stationary ( wrt the rocket ) clock, and the onboard clock shows the same time as the stationary clock, say 12:00.

The rocket rider waits 24 hrs and checks again ( using a telescope of course ) and notices the stationary clock is only showing 11:00.

Since the rocket rider's subjective time hasn't slowed and seems to be running normally ( to him ), it APPEARS the stationary clock has jumped back one hour.

IT HAS NOT !

It has simply moved slower ( as measured from the rocket's frame ) such that only 23 hrs have elapsed in ( the rocket frame's ) 24 hrs.

No clock will ever actually move backwards.

( I think even grampa's own graphic uses the wording 'appears to' )

 

I think we have to use clocks with a day counter, too, in such an example, and nobody would make this kind of mistake.

[granpa]

look at it from the point of view of the stationary clocks

at first rocket is stationary and all the clocks are in synch with it clock onboard the rocket.

the rocket accelerates to velocity v and is time dilated by gamma

but the clock onboard the rocket is adjusted to run at gamma times faster than normal.

from the point of view of the stationary clocks the rocket is now in synch.

from the rockets point of view all the clocks are out of synch

but when the rocket and a given clock are at the same place at the same time then that given clock must agree with the clock onboard the rocket