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Physics, Astronomy & Cosmology / Re: The dipole problem.
« on: 23/03/2004 14:21:39 »
A little arthmetic with the age of the universe, 13.7 billion years, the hubble constant, Ho = 71 km/s/Mps, and the speed of light, c = 300 megameters/s, give some interesting results. The hubble expansion rate simplifies to 2.3x10(-18)/s. Multiply the age of the universe, 432x10(15)s, c, and Ho, and you get the recessional velocity of the cosmic background radiation. The number is 0.994c.
That simple multiplication is probably wrong, and I should go back and do a relatavistic calculation. I may have also just found an identity here. Anyway, it should be clear that the CBR is receding at nearly the speed of light. That should answer the original question. Astronomers on a galaxy receding at 0.5 C will see a CBR with a low dipole moment, of hundreds of miles/sec. They will see US receding from them at 0.5 C, and wonder what we see when we measure the CBR.
However, it brings up a few other questions. If the CBR is receding at such high speeds, it is highly red-shifted. We measure a 2.7 K black-body radiation that has been red-shifted. What is the non-red-shifted temperature? And could the extremely small variations we see be dependent on small variations in the recessional velocity. In other words, is the recessional velocity truely a constant, or does it have small perturbations that cause us to see small perturbations in the temperature?
That simple multiplication is probably wrong, and I should go back and do a relatavistic calculation. I may have also just found an identity here. Anyway, it should be clear that the CBR is receding at nearly the speed of light. That should answer the original question. Astronomers on a galaxy receding at 0.5 C will see a CBR with a low dipole moment, of hundreds of miles/sec. They will see US receding from them at 0.5 C, and wonder what we see when we measure the CBR.
However, it brings up a few other questions. If the CBR is receding at such high speeds, it is highly red-shifted. We measure a 2.7 K black-body radiation that has been red-shifted. What is the non-red-shifted temperature? And could the extremely small variations we see be dependent on small variations in the recessional velocity. In other words, is the recessional velocity truely a constant, or does it have small perturbations that cause us to see small perturbations in the temperature?