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Question
Hi, just a quick question here. Is the speed of light in vacuum a constant (a) in all reference frames, (b)  in inertial reference frames only or (c) something else?

Thanks.
David

Answer
The speed of light is constant only in "inertial frames of reference", reference frames in which there is no significant acceleration. In addition, the speed of light is also not constant if the light is in an accelerating system such as that near a large gravitational mass such as a black hole or even near the surface of a large star. In fact, for light leaving the surface of star at the center of a black hole the gravitational acceleration reduces the effective speed of the emerging light is zero - thus light cannot escape from a black hole, in fact, why it is a black hole.

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James J. Kovalcin

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I am teaching or have taught AP physics B and C [calculus based mechanics & electricity and magnetism] as well as Lab Physics for college bound students. I have a BS in Physics from the University of Pittsburgh and a Master of Arts in Teaching from same. I have been teaching physics for 34 years. I am constantly updating my skills and have a particular interest in modern physics topics.

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