And that is absolutely 100% accurate, with no measurement errors. But Jack, I hear you say, what are you talking about? The reason we know that that's exactly the speed of light, is that we defined it ...

When Galileo's name comes up, most people think about his contributions to observational astronomy. However, he did lots of other stuff including investigating the speed of light. During his time, ...

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This one has a quick answer and a longer explanation. The quick answer is that there is no absolute point of reference that defines motion for all other objects in the Universe. All of our estimates ...