Understanding the Speed of Light: A Thought Experiment

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Discussion Overview

The discussion revolves around the concept of the speed of light, particularly in relation to different frames of reference and the implications of special relativity. Participants explore thought experiments involving objects moving at significant fractions of the speed of light and the resulting effects on measurements of speed and time.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions whether the speed of light depends on the frame of reference, using a thought experiment involving a ball and a car moving at different speeds.
  • Another participant asserts that the speed of light is constant across all frames of reference, citing it as an axiom of special relativity that has been experimentally verified.
  • A participant seeks clarification on whether light fired from a moving gun would have a slower time interval when observed from another frame of reference.
  • Another participant responds to the previous question by stating that a person traveling at near-light speed will experience time dilation, aging more slowly compared to stationary observers.
  • A further contribution notes that light does not accelerate from rest and always travels at its maximum speed, suggesting that basic mathematical understanding is sufficient to grasp these concepts.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the speed of light in various frames of reference, with some asserting its constancy while others seek clarification on related concepts. The discussion remains unresolved regarding the nuances of time intervals and measurements in different frames.

Contextual Notes

Participants reference concepts such as time dilation and the nature of light's speed without fully resolving the underlying mathematical principles or assumptions involved in special relativity.

bil.a
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I'm still really confused about the speed of light. I'm kinda new at this so bear with me. Does the speed of light depend on the frame of reference it is in? For example let's say you have a ball moving at 10m/s in a car moving at 20m/s. This would mean that from the Earth's frame of reference the ball is moving 30m/s.

But what if you had a car moving half the speed of light. And a man in the car fired a light gun traveling at the maximum speed of light. What would the speed of the light from the gun be from the Earth's frame of reference.

Wouldn't it be 1.5 the speed of light? Why or why not is this not possible?
 
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Welcome to PF.

bil.a said:
Does the speed of light depend on the frame of reference it is in?

It doesn't. Actually, that is one of the axioms that the whole of special relativity follows from, and it is experimentally verified to great accuracy. That is, in two "equivalent" frames (moving with constant velocity with respect to the other) the speed of light always has some fixed value, c.

Now, when you perform your thought experiment, all kinds of weird stuff follows (like, when you use the light gun in your moving car to construct a clock, it will tick slower to a spectator along the track).
 
hmmm so does this mean that the light fired from the gun will move have a slower time interval once it reaches maximum speed observed from the earth?
 
bil.a said:
hmmm so does this mean that the light fired from the gun will move have a slower time interval once it reaches maximum speed observed from the earth?
Not usre what you mean by a "slower time interval," but a person traveling at enar lightspeed will age more slowly, yes.
 
Also note it doesn't reach its maximum speed. It just always travels at that speed, light is not something that needs to be or even can be "accelerated from rest".

May I ask how your mathematical knowledge is? E.g. what is your level of algebra? Because I have a document that allows you to figure out some of the weirdnesses, starting from basic postulates for yourself. I'm not sure where you are from, but in American terms end-of-high school (~ 16 - 18 years of age) math definitely suffices (as long as you can substitute and simplify fractions, and use a function prescription to sketch a graph and derive basic properties from it.).
 

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