Brent Meeker <meekerdb@verizon.net> wrote:

I don't follow that? Are you calculating that, because of the expansion rate, a place 5e4lyr (0.015megaparsec) away will be moving away from us at about 1km/sec /and therefore the CMB won't look isotropic from there?/

No, I was saying the exact opposite of that. Since the CMB looks isotropic from everywhere as long as you're at rest relative to galaxies that are close to you, and since places at rest relative to galaxies that are close to them are moving away from each other at a rate proportional to their distance apart, the CMB's rest frame must be different in different places. So if there's a ring a constant 1 megaparsec in radius (the ring is not expanding), and its center is at rest relative to the CMB at that location, then everywhere on the ring will be moving 70 km/sec toward the center relative to the CMB at that point. But of course no part of the ring ever gets any closer to the center.

The expansion is uniform and so looks the same from any point.

Yes, but only if you're participating in the expansion.

Otherwise you could imagine a point 14e9lyr away at which the CMB was stationary relative to you in one direction.

The ring's radius obviously can't exceed the distance to the cosmic horizon. If it was slightly less than that, and of course made of some impossibly strong material so that it wouldn't be torn apart, everywhere on the ring the CMB would look very asymmetrical. Perhaps it would be the same brightness and color temperature as the sun in the direction of the center of the ring, and completely undetectable at all directions more than a degree away from that direction. (Speaking of which, I've often wondered what it would be like on an Earth-like planet in deep space going at close to the speeed of light relative to the CMB. Obviously there's some velocity at which the planet would get the same flux as Earth gets from the sun, but would the bright spot look anything like the sun, and would the peak be in the visible part of the spectrum? Also, how long would it last (by the planet's clocks) before either CMB-drag or the expansion of the universe made the faux sun cold and dark?)