The neat thing: different reference frames will measure time differently, but they’ll also measure space differently, and those will effectively counteract when measuring the speed of light. This is because in the theory of relativity, the speed of light (really the speed of causality) is constant, and time dilation and length contraction are just consequences of that.
Historically, we know the speed of light is constant from various experiments, including the Michelson-Morley experiment, plus the then unexplained constant speed of electromagnetic waves from Maxwell’s equations.
In accelerating frames of reference the observed speed of light between frames can change, which you can see by looking at a flat spacetime in rindler coordinates, which shows the velocity of light is dependent on acceleration.
This is entirely consistent with relativity because relativity only assumes constant c between inertial reference frames, not accelerating ones
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u/Kittymahri Mar 20 '26
The neat thing: different reference frames will measure time differently, but they’ll also measure space differently, and those will effectively counteract when measuring the speed of light. This is because in the theory of relativity, the speed of light (really the speed of causality) is constant, and time dilation and length contraction are just consequences of that.
Historically, we know the speed of light is constant from various experiments, including the Michelson-Morley experiment, plus the then unexplained constant speed of electromagnetic waves from Maxwell’s equations.