Why not 1/300,000,000 or something different constant ( why only light ) ?
In: Physics
Because you need a constant. Something that should never ever change. Which already make pretty much anything material bad. Because any material can get damage by erosion, corrosion, or any form of time related issue. Matter will always change over time. There is nothing we can use that is forever.
But one of the only constant we can rely on is the speed of light. So we use it as a benchmark.
As for why not to use a round number, it’s a matter of history and practicality. While I say anything material is bad, it doesn’t mean it wasn’t used. At some point we didn’t know the speed of light, nor that it had a speed. Yet we still needed a benchmark. So we used plenty of other benchmark, but none of them were “permanent”. Nonetheless, once we realized we could use the “somewhat perfect” speed of light, we decided NOT to change the actual size of the meter too much. Changing it might mean that every other previous size related thing would become incorrect. Suddenly the house you bought is considered slightly bigger, average changes, etc…
So instead they simply changed the scale. They adapted the scale to fit the previous assumptions. For most people, it meant that nothing changes. Your ol’ ruler is still correct enough, while we’re certain now that this scale is not at risk to change.
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