Calculating Absolute Velocity at 50% the Speed of Light

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Discussion Overview

The discussion revolves around the concept of absolute velocity while traveling at a significant fraction of the speed of light, specifically at 50% the speed of light. Participants explore whether it is possible to measure differences in the speed of light using a spherical shell with reflectors and if such measurements could indicate absolute velocity and direction of travel.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant questions if, while moving at 50% the speed of light in a spherical shell, they would measure differences in the speed of light between reflectors on the shell's perimeter.
  • Another participant asserts that absolute velocity does not exist, emphasizing that all velocities are relative and that the speed of light remains constant for all observers.
  • A different participant explains that, according to Einstein's theory, the speed of light is always measured as c, regardless of the observer's motion, thus making the measurement of relative velocity between the observer and light nonsensical.
  • One participant references the Michelson-Morley experiment, suggesting that it demonstrated the constancy of light speed in all directions, which aligns with the initial question about measuring velocity.
  • Another participant mentions an animation illustrating the scenario, indicating that light does not strike all mirrors simultaneously from the observer's frame, but implies that if it could be measured, absolute velocity could be determined.

Areas of Agreement / Disagreement

Participants express disagreement regarding the existence of absolute velocity, with some asserting it is impossible to measure while others explore the implications of their thought experiments. The discussion remains unresolved with multiple competing views on the topic.

Contextual Notes

Participants reference the principles of special relativity and the implications of the Michelson-Morley experiment, but there are unresolved assumptions regarding the nature of measurements and the implications of relativistic effects.

ThinkThrice
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In the spirit of this forum I should first announce:
-generally, I have no idea what I'm talking about but look for you folks to enlighten me.

Question:
If I am traveling at a significant fraction of the speed of light and I wish to know my current absolute velocity can I use the speed of light in different directions?

If I'm moving at 50% the speed of light in some direction
and I build a spherical shell with reflectors facing the center of the shell
and I stand in the center of the shell and move with the shell with a stopwatch and shine a light at reflectors all around me in my shell
1 - would i measure differences in the speed of light between different reflectors on the perimeter of the shell?
2 - if that's possible couldn't I measure my absolute velocity and determine the direction I'm travelling?
 
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There's no such thing as absolute velocity; velocity is relative. (More precisely, any velocity less than the velocity of light is relative.)
 
Thanks for the response - blows my mind!
 
ThinkThrice said:
1 - would i measure differences in the speed of light between different reflectors on the perimeter of the shell?
2 - if that's possible couldn't I measure my absolute velocity and determine the direction I'm travelling?

The answer to #1 is "no", and therefore #2 is not possible.

Any observer who is moving at a constant speed is entitled to think of himself as at rest and everyone else as moving in the opposite direction. This follows from Einstein's two postulates of special relativity, and is confirmed by an enormous amount of experimental evidence.
 
Einstein's Theory of Relativity is based on two principles and one of them says "No matter how fast you are moving, the speed of light always remains the same for you i.e. c".
For example, if you are traveling at the rate of 2*108 m/s, relative to earth, then essentially, the relative velocity between you and the light should be 1*108 m/s. But it doesn't happen, light always travel at c and you see the light waves passing you at the same speed as you are in rest.
So, measuring the difference in velocity between you and the light waves (relative velocity between you and light) doesn't make any sense because it is always constant and is always equal to c...
 
ThinkThrice said:
In the spirit of this forum I should first announce:
-generally, I have no idea what I'm talking about but look for you folks to enlighten me.

Question:
If I am traveling at a significant fraction of the speed of light and I wish to know my current absolute velocity can I use the speed of light in different directions?

If I'm moving at 50% the speed of light in some direction
and I build a spherical shell with reflectors facing the center of the shell
and I stand in the center of the shell and move with the shell with a stopwatch and shine a light at reflectors all around me in my shell
1 - would i measure differences in the speed of light between different reflectors on the perimeter of the shell?
2 - if that's possible couldn't I measure my absolute velocity and determine the direction I'm travelling?

Ha! You are following the thinking of some great men. That is exactly what people thought. That is why the Michelson-Morley experiment, where they bounced light off reflectors in different directions, confused everyone by measuring the exact same time in all directions.
 
ThinkThrice said:
In the spirit of this forum I should first announce:
-generally, I have no idea what I'm talking about but look for you folks to enlighten me.

Question:
If I am traveling at a significant fraction of the speed of light and I wish to know my current absolute velocity can I use the speed of light in different directions?

If I'm moving at 50% the speed of light in some direction
and I build a spherical shell with reflectors facing the center of the shell
and I stand in the center of the shell and move with the shell with a stopwatch and shine a light at reflectors all around me in my shell
1 - would i measure differences in the speed of light between different reflectors on the perimeter of the shell?
2 - if that's possible couldn't I measure my absolute velocity and determine the direction I'm travelling?
I made an animation to illustrate what would happen in a scenario like you describe:

https://www.youtube.com/watch?v=S7r5GeIfZas

Now you will note that the light does not strike all the mirrors at the same time in the frame in which you are moving at 50%c but that is something that is outside your realm of measurement. If you could, then you would be able to measure your absolute velocity and determine the direction you are traveling.

If you want to see more animations developing conceptually the Michelson-Morley experiment that FactChecker mentioned, check out this thread:

"www.physicsforums.com/showthread.php?t=626807"
 
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