Relativity: Jo Jo left his brain ...

Joel Achenbach has a speed of light post in his Column/Blog in the WaPo.
My editor, Tom, whose last contribution to the blog brought him only misery and derision, has hit me with an imponderable speed-of-light question, to wit:

"According to Einstein (I think), the velocity of light is the one constant in the universe, and everything else, including time, is relative. But isn't velocity a function of time? You can't say what the velocity of anything is without using units of time. So if time is relative, how can velocity be absolute? OK science wonks, and I know you are out there, let the savaging begin!"

I have to confess that the question makes my head hurt. Just like Tom's editing. It would take me several hours to put together an answer for Tom, and then it would be wrong, and I'd have to call up Brian Greene, who probably has better things to do than be pestered by the likes of me.
Well Joel, rather than bother Brian, or inflict your nonsensical musings on the readership, you could do Tom, Brian, and yourself a favor and just buy two copies of Brian's Book, Fabric of the Cosmos, expensed to the WaPo, and read the first two chapters which explain it all.

Or, very briefly, just note that while the speed of light is absolute, and time and distance are relative, not everything else is. Invariant mass, interval and many other things called Lorentz scalars don't change with reference frame. Distance and time are relative in a very precise sense, such that velocity = distance divided by time is constant for anything going at the speed of light.

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