At Speed of Light: Standing Still?

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Discussion Overview

The discussion revolves around the hypothetical scenario of accelerating an object to the speed of light and the implications of such a scenario on the object's state of motion. Participants explore concepts related to relativity, the nature of rest frames, and the fundamental laws of physics regarding the speed of light.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • One participant proposes a scenario where an object could be accelerated to the speed of light and then decelerated to a complete stop, questioning if it would then be standing still in the universe.
  • Several participants assert that accelerating a massive object to the speed of light is impossible, citing fundamental laws of physics and the postulates of relativity.
  • Another participant argues that the object is already at rest in its own rest frame, suggesting that the question may be unnecessary.
  • Some participants emphasize that ignoring the laws of physics leads to nonsensical conclusions, comparing it to asking hypothetical questions that contradict established mathematical truths.
  • One participant elaborates that the impossibility of reaching light speed is a consequence of relativity, stating that the question lacks coherence if one disregards these principles.
  • A different approach is suggested, where instead of attempting to reach light speed, one could measure light speed using mirrors and clocks, adjusting the inertial reference frame to maintain a state of rest with respect to light beams.

Areas of Agreement / Disagreement

Participants generally disagree on the feasibility of accelerating an object to the speed of light, with some asserting it is impossible while others explore the implications of such a scenario. The discussion remains unresolved regarding the hypothetical situation presented.

Contextual Notes

The discussion hinges on the assumptions of relativity and the nature of motion, with some participants challenging the premise of the original question as self-contradictory. There are unresolved implications regarding the definitions of rest and motion in the context of relativistic physics.

Ronnu
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What if we would be able to speed up and object to the the speed of light. Then at the speed of light that object could be moving only in one direction because otherwise it would need to move faster than the speed of light. Now say we would de-accelerate that object but so that the de-acceleration would only be in the opposite direction of the movement of the object and would cease when the objects velocity reached zero. Also let's assume that there are no other forces (gravity etc.) acting upon the object. Wouldn't that body now be standing completely still in the universe?
 
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Ronnu said:
What if we would be able to speed up and object to the the speed of light.
You can't. Anything based on the assumption that you can is therefore nonsense, I'm afraid.
 
Why bother speeding it up and slowing it down? It is already standing completely still in its rest frame.
 
Ibix said:
You can't. Anything based on the assumption that you can is therefore nonsense, I'm afraid.
Ignoring that fact, if you prefer
 
Ronnu said:
Ignoring that fact, if you prefer
You can't ignore a fundamental law of physics, not and get any sense out of it. It's like asking what would maths be like if 1+1 were not equal to 2. You can invent any answer you like. It won't have any relation to the real world, however.
 
A bit more detail. The fact that a massive object cannot be accelerated to the speed of light is a direct consequence of one of the two postulates of relativity, the invariance of the speed of light. If you want to ignore that fact you are throwing out relativity theory, then asking what it would predict about a universe where it doesn't apply. The question is self-contradictory, so there isn't a coherent way to answer it.

The only way to make the question coherent is to make up a complete physics for a universe where relativity does not apply. But that's an imaginary universe, so there are absolutely no restrictions on what those rules are and the results are not related to the real world.
 
Instead of trying to speed up an object to light speed, just use some mirrors and clocks to measure the light speed itself and adjust your inertial reference frame so that you always measure the light speed to be c (which you will find surprisingly easy to do)... in fact you should measure light radiating out in orthogonal directions to be sure you don't overlook any displacements with a lateral component with respect to the original light's beam direction (getting all the other light direction measures to be c will also be surprisingly easy), so now you are standing completely at rest with respect to light beams moving at c away from you in various directions.

Is it a coincidence that this was so surprisingly easy that you needed no velocity adjustments at all to get the light beams all moving away at c?
 
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