Time Dilation happens on moving frame - but which one?

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Discussion Overview

The discussion revolves around the concept of time dilation in the context of special relativity, particularly focusing on the relative perceptions of time between two moving frames. Participants explore the implications of time dilation when both frames are in motion relative to each other, and how this relates to the twin paradox.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that according to special relativity, time in a moving frame R' runs slowly compared to a stationary frame R, but questions how this applies when viewed from the moving frame R'.
  • Another participant asserts that each frame measures the same clock rate for the clock that moves in that frame, suggesting a symmetry in time dilation.
  • A participant emphasizes that both frames observe time dilation in the other, highlighting that time dilation is relative and not absolute.
  • Discussion of the twin paradox is introduced, with a participant mentioning that asymmetry arises when one twin returns, necessitating a change in velocity.
  • Concerns are raised about the lack of consideration for acceleration or gravitational effects in some explanations of the twin paradox.
  • Another participant questions the basis for asserting that the spaceship twin is younger, asking if this has been experimentally verified or is purely theoretical.
  • Responses indicate that while direct experiments with spaceships have not been conducted, similar effects have been observed with subatomic particles.
  • Participants are directed to existing resources and discussions on the twin paradox, indicating that the topic has been extensively covered in the forum.

Areas of Agreement / Disagreement

Participants express differing views on the resolution of the twin paradox and the implications of time dilation. While some assert that the topic is well understood, others feel it remains unresolved and question the experimental basis for claims about time dilation.

Contextual Notes

Limitations include the lack of consensus on the implications of acceleration in the twin paradox and the dependence on interpretations of time dilation in relative motion scenarios.

controlfreak
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As per theory of special relativity the time in moving frame R' is supposed to run slowly compared to the stationary frame R. But isn't the stationary frame R moving wrt frame R' in the opposite direction. For an observer in stationary frame R', R would be moving with the same velocity wrt to it and wouldn't he think time will dilate in R which is the moving frame according to that observer in frame R'? So if time dilates in both, wouldn't both measure the same time? This has been confusing me for a while though I understand the equations which Lorentz framed to satisfy the absolute velocity of flight.
 
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controlfreak said:
wouldnt both measure the same time?
Yes, each frame measures the same clock rate for the clock that moves in that frame.
 
controlfreak said:
As per theory of special relativity the time in moving frame R' is supposed to run slowly compared to the stationary frame R. But isn't the stationary frame R moving wrt frame R' in the opposite direction. For an observer in stationary frame R', R would be moving with the same velocity wrt to it and wouldn't he think time will dilate in R which is the moving frame according to that observer in frame R'? So if time dilates in both, wouldn't both measure the same time? This has been confusing me for a while though I understand the equations which Lorentz framed to satisfy the absolute velocity of flight.

If two frames are moving wrt each other, then they both observe time dilation in the other frame - in the sense that both observe clocks and any physical processes (hence time itself) running slower in the other frame. Time dilation, like motion itself, is relative, and not "absolute".

Also, "moving frame" is relative not absolute; a frame can only move relative to another and is not absolutely "moving".

Understanding how and why this symmetry of time dilation can be resolved is a central aspect of understanding SR. It can be done by the using the Lorentz Transform or by directly studying the behaviour of clocks in the two frames relative to each other.
 
I realize I was talking about the twin paradox. The explanation as given in this link is that (http://en.wikipedia.org/wiki/Twin_paradox) asymmetry is introduced when the twin returns back to compare the times as to return back one needs a change in velocity, an acceleration.
 
This provides an analysis of Twin Paradox resolutions - http://www.iisc.ernet.in/~currsci/dec252005/2009.pdf - This whole thing doesn't seem to be fully and satisfactorily resolved. First of all why do we make the assertions that the spaceship twin is younger? Has that been proved by experiments which indirectly attest to that? or does theory predict that?
 
controlfreak said:
I realize I was talking about the twin paradox.
Use the search function then. It has been explained to death here.
 
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controlfreak said:
This whole thing doesn't seem to be fully and satisfactorily resolved.

That's not correct; it is.

controlfreak said:
why do we make the assertions that the spaceship twin is younger? Has that been proved by experiments which indirectly attest to that?

We haven't done it with spaceships, obviously, but we've done it with subatomic particles many times. As A.T. says, use the PF search function; you will find many, many threads where the twin paradox has been discussed to death. Another good discussion is the Usenet Physics FAQ article on the twin paradox (which you will also find linked to in many of those other threads):

http://math.ucr.edu/home/baez/physics/Relativity/SR/TwinParadox/twin_paradox.html

Pay particular attention to the "spacetime diagram analysis"; that is the most general method of analysis and generalizes to all possible scenarios in curved spacetime as well. It also, as the FAQ article says, allows you to put all the other methods of analysis in their proper perspective.

If you have further questions after reading through what's already been written and discussed, please start a new thread with a specific question. This thread is closed.
 
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