The constancy of the speed of light was also implied by James Clerk Maxwell’s electromagnetic theory. In a sense, Maxwell’s theory was the first unified theory in physics: the great Scottish physicist used the criteria of mathematical beauty and symmetry to blend the existing theories of electricity and magnetism into a set of equations that showed that each was an aspect of the other. These equations showed that vibrating fields of electricity and magnetism progressed through space in the form of waves—of light, heat, or radio waves—with a velocity that was a constant of nature and was
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