This question already has an answer here:

What limits on the time-variance of the CMB do the COBE, WMAP, or Planck data put?

In other words, I am looking for a peer-reviewed paper that would answer this question: If I made maps of, say, WMAP Month 1, Month 2, Month 3, … data, would the timescale of the time-variance between the maps of the different months be much less than than cosmological timescales (say, the Hubble time)?

I do not want an answer that involves cosmology. I want a purely observational answer.


marked as duplicate by Pulsar, John Rennie, DavePhD, Kyle Kanos, Brandon Enright Apr 30 '14 at 15:15

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  • $\begingroup$ Hi Geremia: I believe the specific-reference tag does not apply, cf. its tag wiki. $\endgroup$ – Qmechanic May 1 '14 at 11:49
  • $\begingroup$ @Qmechanic: Ah, I see; it doesn't apply for reference requests. thanks $\endgroup$ – Geremia May 1 '14 at 15:10
  • $\begingroup$ There is a ~0.3 milli-Kelvin seasonal variation of the CMB due to Earth's orbital velocity. This is mentioned in [Anisotropies of the Cosmic Microwave Background](cds.cern.ch/record/580572/files/0209215.pdf) $\endgroup$ – DavePhD May 1 '14 at 15:31
  • $\begingroup$ Geremia: Pulsar's answer in the linked duplicate provides the answer to your question: There is no such evidence/data now, but it could be found a hundred years from now (read the link Pulsar gives, it's well worth it). $\endgroup$ – Kyle Kanos May 10 '14 at 11:16

This answers the original, unedited question:

What is a good paper—using COBE, WMAP, or Planck data—that shows that the CMB anisotropies do or do not vary on timescales much shorter than cosmological timescales (say, the Hubble time)?

I am letting it stand because now above is another question.

In cosmology, a Hubble volume, or Hubble sphere, is a spherical region of the Universe surrounding an observer beyond which objects recede from that observer at a rate greater than the speed of light due to the expansion of the Universe.1

The comoving radius of a Hubble sphere (known as the Hubble radius or the Hubble length) is c/H_0, where c is the speed of light and H_0 is the Hubble constant. The surface of a Hubble sphere is called the microphysical horizon,2 the Hubble surface, or the Hubble limit.

In this review paper it is the Hubble radius ( actually Hubble time multiplied by c ) that controls whether anisotropy will appear in CMB.

On scales large compared to the Hubble radius at last scattering, only gravity is important but on smaller scales the acoustic physics of the primordial plasma and photon diffusion dominate.

So there is a different behavior of the regions of the universe as it is expanding and it is reviewed in the paper.

  • $\begingroup$ But what sort of limits do COBE, WMAP, or Plank put on the time-variance of the anisotropy? $\endgroup$ – Geremia May 1 '14 at 7:08
  • $\begingroup$ as far as the map goes the anisotropies are seen at a fixed time t when the data were taken. It is a photograph, a snapshot, of the time when radiation decoupled. So to get time changes you would have to estimate the radius of the universe at that time (see for evolution of universe abyss.uoregon.edu/~js/cosmo/lectures/lec20.html ) at 500.000 years . You could estimate the delta(t) for the anisotropies by dividing the hubble radius with c. It is not usually done because it carries no information other than whether the regions can communicate or not. $\endgroup$ – anna v May 1 '14 at 7:26
  • $\begingroup$ the answer linked as duplicate addresses your edited question. In a hundred years maybe some variation might be detectable , is my summary. $\endgroup$ – anna v May 1 '14 at 8:30
  • $\begingroup$ I want also to note that your edited question changes drastically the pov. You were talking of hubble time and that is the content of my answer. $\endgroup$ – anna v May 1 '14 at 8:32
  • $\begingroup$ Thanks. I added "cosmological timescale"/"Hubble time" back in. $\endgroup$ – Geremia May 1 '14 at 15:12

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