Time Travel: Lorentz Invariance & Possibilities

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Discussion Overview

The discussion revolves around the concept of time travel, specifically examining whether Lorentz invariance rules out the possibility of traveling back in time. Participants explore the implications of time reversal in the context of Lorentz transformations and the physical interpretation of time.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • Some participants question if going back in time is fundamentally ruled out by Lorentz invariance.
  • There is a request for clarification on what is meant by "going back in time," with distinctions made between physical transportation and the concept of literally turning back time.
  • A participant suggests substituting t → -t in Lorentz transformations to explore changes in the metric, raising questions about the implications of such substitutions.
  • Another participant notes that negating the time component does not affect the spacetime interval, suggesting that negative time is mathematically permissible.
  • Concerns are raised about whether all mathematical solutions can be applied to the real universe, advocating for cautious language regarding implications.
  • A participant seeks to understand the physical interpretation of time and inquires about theories that might allow for particles to travel back in time.
  • It is stated that there are no accepted theories that support the notion of time travel into the past as a real possibility.

Areas of Agreement / Disagreement

Participants express differing views on the implications of Lorentz invariance for time travel, and there is no consensus on whether time travel into the past is possible or what it would entail.

Contextual Notes

Discussion of time travel into the past is generally restricted within the forum, which may limit the exploration of certain ideas and theories related to this topic.

John Fennie
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Is going back in time fundamentally ruled out by Lorentz invariance? Or not? Or is it something else?
 
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What exactly do you mean by "going back in time"?
 
Nugatory said:
What exactly do you mean by "going back in time"?
Either as a physical transportation, or literally turning back time.
 
John Fennie said:
Either as a physical transportation, or literally turning back time.

Try it. Substitute t → -t in any of the Lorentz transformation. Has anything changed?

Zz.
 
ZapperZ said:
Try it. Substitute t → -t in any of the Lorentz transformation. Has anything changed?

Zz.
Take t to be positive, the metric will then have all positive (or all negative) components, hence no time component.
But I am not sure what you are trying to have me see.
 
John Fennie said:
But I am not sure what you are trying to have me see.
The t term in the metric is squared. Negating its sign has what effect?
 
jbriggs444 said:
The t term in the metric is squared. Negating its sign has what effect?
It does not have any effect on the spacetime interval, which means that having negative t is allowed.
 
John Fennie said:
which means that having negative t is allowed.
Do you believe that all possible mathematical solutions apply to the real Universe?
You should, perhaps replace "means" with "could imply".
 
sophiecentaur said:
Do you believe that all possible mathematical solutions apply to the real Universe?
You should, perhaps replace "means" with "could imply".
I understand. How do you guys interpret time physically? Because even time reversal is allowed, how can one physically have say, a particle, go back in time? Is there any sort of theory on the physical applications for going backward? (Just like traveling in a spaceship is a physical application for going forward.)
 
  • #10
John Fennie said:
How do you guys interpret time physically?

That which a clock measures.

John Fennie said:
Because even time reversal is allowed, how can one physically have say, a particle, go back in time? Is there any sort of theory on the physical applications for going backward? (Just like traveling in a spaceship is a physical application for going forward.)

There are no accepted theories that unambiguously accept or suggest that time travel into the past is a real possibility.

Note that discussion of time travel into the past is generally not allowed here at PF.

Thread locked.
 

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