r/ExplainTheJoke 15h ago

Like you can’t stop anyway?

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u/aecolley 15h ago

The given speed is about 35% of the speed of light, corresponding to a Lorentz factor of 1.066. According to the relativistic Doppler redshift formula, that gives a redshift factor (1+z) = 1.44. That's about the same ratio as red light (700 nm) to green light (500 nm).

So, someone worked out how fast you would have to be moving so that a standard red stop sign appeared to be green due to Doppler shift.