FTL Signals and the Paradox of Causality

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Discussion Overview

The discussion revolves around the implications of faster-than-light (FTL) signals on the principle of causality, exploring how such signals could lead to scenarios where information travels backward in time. The scope includes theoretical considerations related to relativity and the potential paradoxes arising from FTL communication.

Discussion Character

  • Debate/contested

Main Points Raised

  • Some participants propose that FTL signals could violate causality by allowing information to travel backward in time in different reference frames.
  • One participant questions the concept of "experiencing time dilation" and suggests that if FTL signals were possible, both Earth and a high-speed spacecraft could perceive each other's signals as traveling backward in time.
  • Another participant describes a scenario involving a spacecraft traveling at 0.95c and its implications for message transmission between the spacecraft and Earth.

Areas of Agreement / Disagreement

Participants express differing views on the nature of time dilation and the implications of FTL signals, indicating that multiple competing perspectives remain unresolved.

Contextual Notes

Limitations include assumptions about the feasibility of FTL signals and the definitions of time dilation, which are not universally agreed upon in the discussion.

Sanders
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This is a pretty basic concept of relativity that used to make sense to me but I have since become a little unclear on the issue.

The question is how can one violate the principle of causality simply by broadcasting information that travels faster-than-light?
 
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Because a FTL signal going forward in time in one reference frame will go backwards in time in some other reference frame.
 
Originally posted by Hurkyl
Because a FTL signal going forward in time in one reference frame will go backwards in time in some other reference frame.

How would you describe this with a high-speed (.95c) spacecraft leaving Earth?

The spaceship, experiencing time dilation, would be sending messages into the past while Earth would be sending messages into the future, correct?
 
There is no such thing as "experiencing time dilation"...

Anyways, that aside, (assuming it is possible to send FTL signals) it is possible both for the Earth to send an FTL signal which the spaceship perceives as going backwards in time, and it is possible for the spaceship to send a FTL signal which Earth would perceive as going back in time.
 

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