Speed of Light -- Why doesn't it add to the speed of the emission source?

[PhDnotForMe]

My question is about the speed of light. Our current understanding of light says that light is constant for all observers, and uses time dilation to explain this. Have we proven this? The speed of light emitted from a stationary object is equal to C. The speed of light emitted from a moving object is also equal to C with respect to the moving object. Have we proven that the speed of the light emitted from the moving object is equal to C with respect to any stationary object rather than C+the speed of the moving object?

 

[BvU]

Fap&tp: yes

Fap&tp meaning: for all practical and theoretical purposes.

M&M is often cited in this context.

 

[Nugatory]

You could start with this sticky thread from the top of the relativity section: https://www.physicsforums.com/threads/faq-experimental-basis-of-special-relativity.229034/. Everything there is either a direct test of the invariance of the speed of light, or a test of one of the consequences of that invariance.

At this point we are so confident about this that we now define the meter in terms of the speed of light (a meter is the distance that light travels in 1/299762458 seconds) instead of saying that the speed of light is something that we measure once we've defined the length of the meter.

 

[FactChecker]

If you are asking about light coming from an external moving object to a "stationary" object, the first problem is that there is no official "stationary" object. "stationary" is relative. If one assumes that the Earth is "stationary", then your question amounts to asking if the speed of light from moving external stars and visible planets has been measured. There have been several such measurements. The earliest measurements were of that type: http://www.speed-light.info/measure/speed_of_light_history.htm . More recent astronomical measurements have obtained an accuracy of 0.02 parts per billion (https://en.wikipedia.org/wiki/Speed_of_light#Astronomical_measurements ).

 

[Dale]

Have we proven this?

Yes. See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html especially section 3.3.

 

[Ibix]

Have we proven this?

Pedantically, no, because this is a hypothesis you test not a result you prove. It's theoretically possible that an experiment will one day show that this hypothesis is not correct - but certainly the experiments you propose have been done and relativity passes to absurd precision.

 

[Herman Trivilino]

My question is about the speed of light. Our current understanding of light says that light is constant for all observers, and uses time dilation to explain this. Have we proven this?

Have we proven that our understanding is correct? This depends on what you mean by "proven". Different standards are used in different arenas of human knowledge. In science it's not a well-defined concept because what happens is the evidence continues to mount as to whether or not an understanding is correct. If we compare this to what it means to have "proven" something in a court of law, we see a fundamental difference. At some point the prosecution must stop presenting evidence, but in science there is no such restriction.

By the way, there are explanations that don't involve time dilation.

 

[Nugatory]

It's theoretically possible that an experiment will one day show that this hypothesis is not correct

That hypothetical possibility does exist... but if so the replacement hypothesis will not be the one suggested in the first post of this thread, namely "rather than C+the speed of the moving object". That alternative has already been falsified by many experiments.

 

[PhDnotForMe]

That hypothetical possibility does exist... but if so the replacement hypothesis will not be the one suggested in the first post of this thread, namely "rather than C+the speed of the moving object". That alternative has already been falsified by many experiments.

This is actually my exact question. You said it has been falsified by many experiments. The reason I asked the original post is because I cannot find any such experiments. I would be very happy if you would be able to reference these for me! Thanks in advance.

 

[Dale]

You said it has been falsified by many experiments. The reason I asked the original post is because I cannot find any such experiments

See the link I posted in post 5

 

[Vanadium 50]

This is actually my exact question. You said it has been falsified by many experiments. The reason I asked the original post is because I cannot find any such experiments

You could start with this sticky thread from the top of the relativity section: https://www.physicsforums.com/threads/faq-experimental-basis-of-special-relativity.229034/.

See: http://www.edu-observatory.org/physics-faq/Relativity/SR/experiments.html especially section 3.3.

What part of this do you find unsatisfactory? There is a whole section (3.3) on the speed of light from moving sources.