# Why is C constant

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If we are in a rocket flying to the sun at 0.75C, why would we measure light from the sun AND light from earth to be C. It can't be because "moving clocks tick slower" for both cases, can it?

I think that there exists a simple explanation on why when we measure the speed of light we find it to be always c. This explanation is that light is made of photons and photons are massless particles; it can be shown that a massless particle has a speed c always. The conclusion here seems obvious, if a particle 'of light' always has speed c, we cannot measure something different!

Edited by juanrga

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There is a complete explanation about why the speed of light is constant at:

http://en.wikibooks.org/wiki/Special_Relativity/Spacetime#The_modern_approach_to_special_relativity

Take a look and be enlightened. Basically the speed of light is constant because the universe is four dimensional and the fourth dimension enters into Pythagoras' Theorem with a negative sign. Take a look at the link, it explains it better than I could.

DrRocket said that ether theories were equivalent to Relativity: " Simply choose a reference frame and by fiat demand that all other reference frames are related to it by the usual Lorentz transformations."

This seems to miss an important point:

"It is also popular to claim that Special Relativity and aether theories such as those due to Poincaré and Lorentz are equivalent and only separated by Occam's Razor. This is not strictly true. Occam's Razor is used to separate a complex theory from a simple theory, the two theories being different. In the case of Poincare's and Lorentz's aether theories both contain the Lorentz Transformation which is already sufficient to explain the Michelson and Morley Experiment, length contraction, time dilation etc. without an aether. The aether theorists simply failed to notice that this is a possibility because they rejected spacetime as a concept for reasons of philosophy or prejudice. In Poincaré's case he rejected spacetime because of philosophical objections to the idea of spatial or temporal extension (see note 1)."

There is no need to introduce an aether if you demand by "fiat" that the Lorentz Transformations apply.

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