We sometimes speak rather carelessly about 'the speed of light' when we actually mean the speed of light in a vacuum,, the fundamental physical constant, c. The speed of light in a medium is another matter completely. When light enters a medium like air, water or glass, it slows down. It is therefore perfectly possible, for example, for a subatomic particle to travel faster than the speed of light IN WATER - and many thousands of people have seen the evidence. A water-moderated nuclear reactor will glow with a rather pretty blue colour as the result of Cerenkov Radiation - the light analog of a sonic boom when an object travels through air faster than the speed of sound.
Was this what you were asking about?
Was this what you were asking about?
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No the speed of light depends only on the relative density of the medium it travels through. The mass is irrelevant. Light travels slightly slower through water (denser than air).
However the change in speed is also wavelength dependent and red light is refracted less than blue light.
Furthermore the speed of light is constant irrespective of the speed of the observer. For example if you had two trains traveling at the same speed (so the relative speed of one train as seen from the other is zero) the speed of light would still be the same. This is the peculiarity of light compared to bodies that have mass.
However the change in speed is also wavelength dependent and red light is refracted less than blue light.
Furthermore the speed of light is constant irrespective of the speed of the observer. For example if you had two trains traveling at the same speed (so the relative speed of one train as seen from the other is zero) the speed of light would still be the same. This is the peculiarity of light compared to bodies that have mass.
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Speed of light depends on impedence of the material it goes through. For instance, it travels slower in water than in air, but faster than in glass.
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The speed of light is measured relative to the observer.