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Gravity Probe B

Testing Einstein's Universe

Special & General Relativity Questions and Answers

Is there a theory that predicts the velocity of light?

Not really. I am aware of only one theory that indicates that the speed of light is a quantity that is derivable from two other physical quantities, and that is Maxwell's electrodynamics which is the cornerstone theory of how charged particles and electromagnetic fields operate. In it, the speed of light is the square root of the ratio of the dielectric constant ( epsilon) and the magnetic permeability ( mu) of the vacuum. We do not know how to derive either one, in absolute units, from 'first principles'.


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All answers are provided by Dr. Sten Odenwald (Raytheon STX) for the NASA Astronomy Cafe, part of the NASA Education and Public Outreach program.