Huh? Doppler navigators do work, and were invented long before Cesium clocks were invented. Please explain.
True. That is my point.
It's all true of course, but why are you getting riled up?
Joe Gwinn
Oh! Sorry that wasn't clear to me.
Of course out in space you can measure your relative velocity to that of the (averaged) CMB*. So perhaps in some 'universal' sense we could define some 'zero' velocity. (not very useful here on Earth.)
George H.
*cosmic microwave background
Aha! So the universe *has* a centre then.
Jeroen Belleman
Well not really. :^) You could define a zero velocity at every point in space. Where, 'point' could cover a rather large volume. I had to look up the word, astronomers call this the peculiar velocity.
George H. (I will fully admit I doesn't really understand what it means to live in an expanding universe... if it is expanding...)
Doppler navigators work by sending radio waves /outside/ the box, where they reflect on something /static/ that is /outside/ the box, and are returned to the box.
You cannot make a system that detects speed (or position) from inside a black box. You can detect acceleration (or gravity - they are indistinguishable). That's it. For anything else, you need some kind of contact or reference outside the box, because speed (and position) only makes sense relative to something else.
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