You may. Please Register or Log in to view the hidden image! I'm sure you'll also find my latest post (we cross-posted) very interesting. By looking for the CMB dipole, then measuring how intense it is. The more intense, the faster we're moving relative to the CMB rest frame. If we hadn't found it then everyone would have been quite surprised; it would be very unlikely that the Earth would be at rest with respect to such a frame. It might well have caused us to question whether we had actually detected the CMB, and not some other more local effect, more likely to create a background in which the Earth appeared to be motionless. No, because the CMB rest frame varies from one place to another in the universe. It's only motion relative to the local CMB rest frame. It's only approximately isotropic. There are variations which have been charted with WMAP and Planck, all over the sky. These variations, however, are on the close order of a few percent, and most of them are on the close order of a few tenths of a percent; quite small, for something that violent. You can say it's isotropic and not be far wrong. You can't assert that Earth has "a" proper motion. The question that must be asked when you say this is, "proper motion in what frame of reference?" Because otherwise talking about "Earth's proper motion" is meaningless. The Big Bang was very, very slightly anisotropic; it's an error (and not supported by the evidence of WMAP, Planck, and many earlier experiments going back to the late 1960s (see the paper I linked above)) to state that the Big Bang must have made the universe perfectly isotropic. We can even see that in the galaxies; we now know that they are organized in "filaments" that span hundreds of millions and even up to tens of billions of light years. Those filaments are mostly dark matter, and they were formed as a result of slight anisotropies in the plasma of the Big Bang which later caused slight density fluctuations in the distribution of the dark matter, which were then amplified by gravitational attraction into the filaments we see today. Most if not all of the galaxies have formed along these filaments, as the normal matter was attracted by the dark matter. Sure, man. No problemo. You're asking, and you're polite. I never mind answering polite people. I don't believe in being a dick to people who don't know as much as I do; I actually enjoy it or I wouldn't be here! Please Register or Log in to view the hidden image! Done. Enjoy. Please Register or Log in to view the hidden image!