Relativity Q: Light Beam Speed Relative to Object & Observer

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    Relativity
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Discussion Overview

The discussion revolves around the speed of light relative to a spaceship and an observer, particularly in the context of special relativity. Participants explore scenarios involving a spaceship traveling at the speed of light and at a fraction of that speed, as well as the implications for observers.

Discussion Character

  • Debate/contested, Conceptual clarification

Main Points Raised

  • One participant suggests that if a spaceship is traveling at the speed of light (c) and emits a beam of light, the beam would also be traveling at c relative to the spaceship.
  • Another participant agrees that the speed of light will always be c with respect to any object or observer.
  • A participant challenges the idea of a spaceship traveling at c, stating that it cannot reach that speed but can approach it closely.
  • There is a mention of the Alcubierre warp drive as a theoretical concept that might allow for faster-than-light travel, referencing a specific academic paper.
  • A later reply acknowledges a previous oversight regarding the impossibility of a spaceship traveling at c, indicating a correction in understanding.

Areas of Agreement / Disagreement

Participants generally agree that the speed of light is c relative to any observer, but there is disagreement regarding the feasibility of a spaceship traveling at the speed of light, with some asserting it cannot occur.

Contextual Notes

The discussion includes assumptions about the nature of light speed in relation to different frames of reference and the theoretical implications of warp drive technology, which remain unresolved.

devious_
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If a spaceship is traveling at c and a beam of light is emitted through it. The beam of light would be traveling at c relative to the object. Correct?

How about if there's an observer, what would the speed of the beam of light be relative to him. c?

And if the spaceship was instead traveling at 0.6c, would the speed of light relative to it still be c?
 
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Yes to all: The speed of light with respect to any object or observer will be c.
 
Great. Thanks. :)
 
devious_ said:
If a spaceship is traveling at c

A spaceship can't travel at c, though it can get arbitrarily close.
 
pervect said:
A spaceship can't travel at c, though it can get arbitrarily close.
Well... there is that whole Alcubierre warp drive thingy.

E.g. see Fundamental limitations on "warp drive" spacetimes, Francisco S. N. Lobo, Matt Visser, Class.Quant.Grav. 21 (2004) 5871-5892

Online at - http://xxx.lanl.gov/abs/gr-qc/0406083

Pete
 
devious_ said:
If a spaceship is traveling at c
pervect said:
A spaceship can't travel at c, though it can get arbitrarily close.
Oops... I must have missed that statement by devious_ in my quick reading. Good catch, pervect.
 

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