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by euyyn
3341 days ago
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> Use of any reasonable measuring apparatus will have the built-in assumption that c and h are constant The speed of light was measured constant by the famous Michelson-Morley experiment, whose apparatus didn't have any built-in assumption about c (nor had anything to do with h). |
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One metre is defined to be the length of the path travelled by light in a vacuum in 1/299 792 458 seconds. Therefore, c = 299 792 458 metres per second. The second is defined in terms of the frequency of electromagnetic radiation emitted during a transition between two specific states in a caesium atom. In other words, it's a unit of time as measured on a kind of atomic clock, which by convention is constant.
It's an open question whether a second on a pendulum clock is the same as one measured on an atomic clock for all time, as that depends on G.