Why should the speed of light be the same in every frame of reference.

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Discussion Overview

The discussion revolves around the concept of the speed of light being constant in all frames of reference, exploring implications of this principle in relation to particles moving at relativistic speeds and a car moving at a much lower speed. The conversation includes theoretical considerations and interpretations of relativistic effects such as time dilation and Lorentz contraction.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants suggest that the speed of light relative to a particle moving at 0.98c is not the same as the speed of light relative to a car moving at 50m/s, based on their arrival times at a given point.
  • Others challenge this view by emphasizing the importance of Lorentz contraction and time dilation, arguing that these relativistic effects must be considered when comparing measurements from different frames of reference.
  • A participant reiterates the idea that, regardless of the observer's frame, the speed of light remains constant, noting that measurements from a moving car and a moving particle yield the same speed of light due to relativistic effects.
  • One participant clarifies their earlier statement about "spending more time together," indicating that they refer to the interaction time between light and particles traveling at high speeds.
  • Another participant points out that the light and the particle are only together at the instant they start, suggesting that the light moves at speed c as measured from the particle's frame.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the speed of light being constant across frames of reference, with some asserting that it leads to contradictions in a Newtonian framework, while others maintain that the relativistic perspective resolves these issues. The discussion remains unresolved with multiple competing views present.

Contextual Notes

Participants reference concepts such as time dilation and Lorentz contraction, which are central to the theory of relativity. However, there are unresolved assumptions regarding the interpretation of measurements in different frames of reference.

Lizwi
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If we have light, any particle, and maybe car, the particles travel at 0.98c and car let say 50m/s. Let them start moving at the same time to the given point let say 300 metres away. The difference between times of arrival of light and particle will be small compared to that between light and car. This means that light and particles spend more time together than the time light spend with car, hence the speed of light relative to particle is not the same as speed of light relative to car.
 
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I have no idea what you could mean by "spend more time together".

I suspect your error is that you are not taking into account the Lorentz contraction of time for the particles as seen from the car's frame of reference.
 
Lizwi said:
If we have light, any particle, and maybe car, the particles travel at 0.98c and car let say 50m/s. Let them start moving at the same time to the given point let say 300 metres away. The difference between times of arrival of light and particle will be small compared to that between light and car. This means that light and particles spend more time together than the time light spend with car, hence the speed of light relative to particle is not the same as speed of light relative to car.
You are implicitly assuming a Newtonian universe here, where length and time are absolute.

That the speed of light is experimentally the same to all observers was a big clue that this Newtonian view is not how the universe works, at least not at very high speeds. And indeed, length and time are not absolute.
 
Hi HallsofIvy: By saying they spend more time together I mean it take some time for light to leave these particles back if they are traveling at may 0.9c.
 
Lizwi said:
If we have light, any particle, and maybe car, the particles travel at 0.98c and car let say 50m/s. Let them start moving at the same time to the given point let say 300 metres away. The difference between times of arrival of light and particle will be small compared to that between light and car. This means that light and particles spend more time together than the time light spend with car, hence the speed of light relative to particle is not the same as speed of light relative to car.

If you're sitting in the moving car, and you measure the speed of light, and if your sitting on the particle and you measure the speed of light, you will get the same speed.

This is because time dilates and length contracts in the moving frame of reference WHEN MEASURED BY A FRAME AT REST. When measured from inside the moving frame, time and length are normal. These factors mean that the speed of light is always measured to be the same in all frames, regardless of their relative motion.

BTW, the light and the particle are only together at the instant they start. The light and the particle spend no time together because the light still moves at c, as measured from the particle.
 

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