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Relativity/Is the speed of light not invariant, trough vacuum or trough matter?.

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Question
did Einstein say "the speed of light is not invariant, trough vacuum or trough matter", "if there is gravitation"?

Answer
The speed of light is quite sensitive to the medium through which it moves. It is about 2/3c in glass and 3/4c in water. That is how lenses work. This has been known a long time before Einstein.

Einstein predicted also that the speed of light varies with the gravitational field. That is how the sun bends the path of light very slightly when light from a star passes close to it on its way to earth. This effect is tiny compared to the effect of glass and water.

So I have to say yes to your question.

Ben  

Relativity

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Uncle Ben

Expertise

I can answer questions regarding Einstein's Theory of Relativity, particularly in Special Relativity. I will not answer homework questions or mathematical problems that require special symbols.

Experience

I have taught physics at the college level, undergraduate and graduate, for many years including Special Relativity. I have taught at Johns Hopkins, Case-Western, and MIT. I have also served as a staff member of the Commission on College Physics, which was supported by the National Science Foundation to recommend improvements in the curriculum of college physics departments in the US. I am also the author of a textbook titled Vector Calculus, which was used at MIT in the teaching of electromagnetic theory and relativity. My research interests were mainly in solid state physics, especially the properties of metals at low temperatures. I am listed in the publication known as American Men of Science.

Publications
I have dozens of papers published in the Physical Review and in the American Journal of Physics.

Education/Credentials
I hold a Ph.D. degree in physics from the Johns Hopkins University.

Past/Present Clients
Johns Hopkins University, Case-Western Reserve University, Massachusetts Institute of Technology, Empire State College, Georgetown University, Commission on College Physics, and UNESCO.

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