Question re flat infinite universe with a preferred direction

[Buzz Bloom]

TL;DR

If the universe is flat and infinite, then what is the explanation of the origin of the exact opposite directions of the two nodes in the sky which are the sources of minimum and maximum cosmic microwave background (CMB) radiation? It seems reasonable to suppose that these nodes existed well before the CMB began.

The implication seems to be that from the beginning of the post expansion era, there was everywhere an average velocity of a large volume of matter which was (very near) zero everywhere with respect to a common fixed coordinate system (with a spacially uniform time expansion of distances) throughout the entire infinite universe.

I noticed that the thread https://www.physicsforums.com/threads/is-the-universe-finite-or-is-it-infinite.506986/ did not address this issue. I suggest that a finite hyper-spherical universe would require only a finite volume of a fixed coordinate system. I suppose it is just a matter of personal preference regarding whether an infinite or a finite coordinate system is more capable of producing the finite average velocity everywhere.

 

[andrewkirk]

I presume when you say "if the universe is flat" you are referring to its large scale structure, not suggesting that it be absolutely flat everywhere. ie I presume you mean large-scale flat as opposed to large-scale elliptic or large scale hyperbolic. A universe that is absolutely flat everywhere would have no separated bodies of matter such as planets. In other words I presume you are conceiving a universe that is globally flat but not locally flat.

If so then there's no contradiction between global flatness and a local phenomenon such as the perception on a single planet (Earth) of directions of maximum and minimum CMBR. Global uniformity is about large scale averages in the limit as our measurement scope approaches infinity, and says nothing about local phenomena like those nodes.

 

[Buzz Bloom]

Hi @andrewkirk:

Thank you for your response. Your identifying "if the universe is flat" as referring to "its large scale structure" is exactly what I intended. I appologize for not being as clear as I should have been.

I am somewhat confused by your calling the two nodes in exact opposite positions in the sky as a "local phenomena". I am probably misunderstanding your intent, but your description seems to be saying that if an observer in a different location at some very large distance from our location observed the two nodes, they would likely be in the sky in a different direction than where the nodes we see are. That geometry does not make sense to me. It would plausibly perhaps make some sense if the nodes were not in exact opposite positions in the sky. If the other observer found the two opposite node in exactly the same sky location as we see it, then it would not be reasonable to call it a local phenomenon.

Regards,
Buzz

 

[George Jones]

what is the explanation of the origin of the exact opposite directions of the two nodes in the sky which are the sources of minimum and maximum cosmic microwave background (CMB) radiation?

For the Earth/Milky Way, $v_\mathrm{peculiar} \neq 0$ with respect to the Hubble flow. See the cosmology section of

https://en.wikipedia.org/wiki/Peculiar_velocity

 

[Bandersnatch]

As George said, the temperature dipole in the CMB is just the doppler shift due to the motion of the solar system w/r to the rest frame of the primordial plasma. I.e. the few hundred km/s we ended up accruing as a result of how the structure in the universe has evolved - the Milky Way is moving, attracted by the mass distribution in its neighbourhood, and the Sun is moving on an orbit within it. You get relative blueshift on the one side of the sky and redshift on the other, along the axis of motion.

 

[Buzz Bloom]

Hi @George Jones and @Bandersnatch:

Thank you very much for your posts. I now get the mistake in thinking which I was experiencing. I blame it all on my very advanced years.

Regards,
Buzz