Is time reversal logically consistent?

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Discussion Overview

The discussion revolves around the logical consistency of time reversal within the framework of special relativity, exploring whether observers can perceive time running backwards and the implications of superluminal particles on this concept.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions whether three observers (A, B, and C) can have differing perceptions of time directionality, specifically if A can run backwards in time according to B, and B according to C.
  • Multiple participants assert that time never runs backwards, expressing skepticism about the premise of time reversal.
  • Another participant raises questions about the implications of special relativity (SR) on time reversal, particularly regarding particles traveling faster than light and whether observers in different frames would agree on time directionality.
  • A later reply references a previous discussion suggesting that time reversal may require consideration of different frames of reference, indicating a potential for super-luminal Lorentz boosts.
  • One participant emphasizes that special relativity does not permit any reference frame's time to run backwards according to any other reference frame, reiterating the restrictions of the Lorentz group.
  • Another participant concludes that time reversal is not logically consistent with special relativity, reinforcing the idea that no frame can travel faster than light relative to another frame.

Areas of Agreement / Disagreement

Participants express disagreement on the possibility of time running backwards, with some asserting it is impossible while others explore the implications of special relativity and superluminal particles. The discussion remains unresolved regarding the logical consistency of time reversal.

Contextual Notes

Limitations include the dependence on specific interpretations of special relativity and the unresolved nature of how different frames of reference might perceive time and velocity.

kmarinas86
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If you have three observers A, B, and C, if A is running backwards in time according to B, and B is running backwards in time according to C, does this mean that A must in run in the same direction in time as C, according to C (and/or vice versa)? Or does special relativity allow A to run backward in time according to C (and/or vice versa)?
 
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Time never runs backwards. I don't know where you got that from.
 
DaleSpam said:
Time never runs backwards. I don't know where you got that from.

https://www.physicsforums.com/search.php?searchid=2878677
 
Last edited by a moderator:
Which of those do you believe is related to your question in any substantive way? I.e. Which of those supports your premise that there exists some observer B for whom A's clock is running backwards?
 
DaleSpam said:
Which of those do you believe is related to your question in any substantive way?

Ok, I just changed the post after you replied. Here's the new link:

https://www.physicsforums.com/search.php?searchid=2878677
 
Last edited by a moderator:
It looks like the search results aren't specific enough. So I will simply ask you a few simple questions that rely on less unstated context.

Would, according to SR, time reverse for particles traveling faster than light? Then, if faster than light particles were observed, would observers sharing their frame of reference be consistent in the manner suggested at the beginning of the OP?

kmarinas86 said:
If you have three observers A, B, and C, if A is running backwards in time according to B, and B is running backwards in time according to C, does this mean that A must in run in the same direction in time as C, according to C (and/or vice versa)?

Or not?

kmarinas86 said:
Or does special relativity allow A to run backward in time according to C (and/or vice versa)?
 
Also, note in another thread, I had received the following response:

https://www.physicsforums.com/newreply.php?do=newreply&p=3521551

DrStupid said:
It requires backwards time travel in some frames of reference but not in all frames of reference.

That the scientists at CERN have measured a positive velocity in their own rest frame wouldn't mean that the velocity is positive in every frame of reference.

It appears that he is suggesting that there can be such a thing as a super-luminal Lorentz boost. This has actually been suggested in scholarly papers:

http://scholar.google.com/scholar?hl=en&q="superluminal+lorentz"

But additionally, he seems to imply that whether an object appears to be super-luminal or not can depend on the frame of reference, though this was off a tangent where my main focus was about an observer in the laboratory frame of the recent CERN neutrino experiment.
 
Last edited by a moderator:
Special relativity does not allow any reference frame's time to run backwards according to any other reference frame. Special relativity also does not allow any frame to travel faster than light wrt any other frame.

The symmetry group of SR is the restricted Lorentz group.
 
A: Time reversal is not logically consistent with SR.

DaleSpam said:
Special relativity does not allow any reference frame's time to run backwards according to any other reference frame. Special relativity also does not allow any frame to travel faster than light wrt any other frame.

The symmetry group of SR is the restricted Lorentz group.

Emphasis: "restricted Lorentz group."

Got it. Thank you.
 

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