Re: Relativity Allows Us To Measure Absolute Motion?

Martin Hogbin wrote:

Motion relative to the frame in which the CMBR is locally isotropic
is detectable at every point in the universe but there is nothing necessarily
absolute about this. If you arrange to be in such a frame nothing special
happens (except of course the CMBR is isotropic).

What I was wondering was how a lot of the stuff in the universe happened to end up in such frames, as it were. (Okay, that's really sloppily put, but I hope you know what I mean.)

I've attempted to clarify what I'm trying to get at in my second reply (10:32 UTC, 30/11/07) to Eric Gisse, if that helps.

Compare this with something which does seem to be absolute
such as acceleration. If you arrange to be in a non-accelerating
(inertial) frame, Newton's laws of motion take on a simpler form
that they would do in, say, a rotating (non-inertial) frame.

Okay, yes, I understand that relativity means we don't need absolute-velocity-dependent laws of physics.

Let's imagine being inside a sealed lab. We can't look outside the lab, or measure anything outside the lab. We can only do our measurements and observations inside the lab. We conduct various experiments and derive various laws of physics, but none of this enables us to measure the lab's velocity. We can measure velocities within the lab relative to the lab itself, but we can't establish any kind of absolute velocity for the lab itself.

Now let's have the whole universe as our lab. How come, with no special, preferred places in space, and no special, preferred frames, we end up with such things as the CMBR in our lab? It's as if, following the instant of the Big Bang, we've conducted an experiment that looks like it's allowing us to measure velocities at particular places relative to the universe as a whole.

Does that help clarify what it is I'm trying to get at?

Note that the spacetime of SR is not Euclidean.

Whoops! Yes, I blundered. I meant Minkowskian. It's just the space itself that would be Euclidean, yeah?

No, I think you are just confused about relativity, I am not sure where to start.

Perhaps we could start with what the term "absolute motion" does and does not conventionally mean?

--
Simon G Best
....
What happens if I mention Leader Kibo in my .signature?
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