jcsd
Science Advisor
Gold Member
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Nereid said:To Aether (and yogi): I'm in the slow class today, would you mind patiently explaining how the CMB(R) can be used to establish an absolute frame of reference? I'm particularly interested in seeing how - in principle! - it could be used to create an absolute ruler and clock, oh, and an absolute set of coordinate directions (orthogonal or not) would be nice, as too would an absolute origin for the coordinate system and clock.
Please be sure to explain why the procedures you describe would yield the same results whether I'm here on Earth, somewhere in the Bootes void, orbiting M87's SMBH (just so I don't get sucked in), or somewhere in the vicinity of one of the primordial galaxies in the HUDF field (z ~=8). {Garth's cosmological paradox method is not permitted; you can't assume anything about the geometry}
Thik about FLRW cosmology, we assume that the universe is both homogenous and isotrpic as that is indeed as it appears to be. However hopefully it shouldn't be a major leap to see that there's only going to be one frame in which it is isotropic, so by using the assumption it is isotropic when building our models of the universe we are looking at one frame in particular, which can be defiend by observing the CMBR.
In some sense this frame is special i.e. because it's isotropic, but that does not go against the general principle of relativity as the basic laws of physics are still the same in each frame and the existence of the frame whilst it does allow you to define quite a useful clock and quite a useful distance, doesn't define an absolute clock or absolute distance.
Of cpourse it is fair to question the principle of general relativty, but most cosmologists don't see any conflcit between the existence of this frame and the principle of relatvity.
(it is late Friday night here, but that's no excuse)