What "blobs" caused CMB anisotropies ?

[Widdekind]

The degree-scale anisotropies observed on the CMB (few parts per million) at redshift (z~1000) correspond to volumes of space, at present epoch (z~0), hundreds of Mpc across.

 

Please ponder, that the CMB anisotropies are a degree across, at (z~1000); in their immediate foreground (z~10), cosmically almost as far away, proto-galaxies are tens of thousands of times smaller, only tenths of arc-seconds across. That's like a coin on a football field, as compared to the entire stadium; or a transiting exoplanet, as compared to its star.

 

Whatever were the "blobs" which generated the CMB anisotropies, they have expanded today into vast volumes of space, larger than the scale of cosmic uniformity / homogeneity / isotropy. Hot or cold, all of the "blobs" formed statistically the same number of galaxies & stars, structures & voids.

 

What were those "blobs" then? What are their descendants now? If cosmologists say that space is uniform on 100Mpc scales; and if the CMB anisotropies correspond to even larger size scales; then what is the relation between CMB anisotropies then, and (any) known structures not?

[mathematic]

blobs = quantum fluctuations?

[ajb]

The current best thinking is that, as mathematic points out, quantum fluctuation in the inflaton and/or curvaton field generated the anisotropies. Such models match the observed CMBR anisotropies well, though details of the exact models cannot yet be distinguished. Any modern theory of cosmology must allow for inflation and match the power spectrum of the CMBR fluctuations.

 

Cosmic strings were once thought to be a candidate for the seeding of large scale structure. However, details of the CMBR don't match the predictions here. Cosmic strings are now not though to be the dominant course of the anisotropies, though they may still pay a role, see for example [1].

 

In principle, one should be able to match the anisotropies to observable structures in the early universe. There has been work in this direction, see [2] as an example. I am not very familiar with the current status of the correlation and you should do a literature search as I know more papers on this subject have been published.

 

References

 

[1] Neil Bevis, Mark Hindmarsh, Martin Kunz and Jon Urrestilla, Fitting CMB data with cosmic strings and inflation, Phys.Rev.Lett.100:021301,2008. (arXiv:astro-ph/0702223v3 )

 

[2] Shirley Ho, Christopher M. Hirata, Nikhil Padmanabhan, Uros Seljak and Neta Bahcall, Correlation of CMB with large-scale structure: I. ISW Tomography and Cosmological Implications, Phys.Rev.D78:043519,2008. (arXiv:0801.0642v2 [astro-ph])

[Widdekind]

Cosmic strings & inflation are speculations, yes? No observations connect one-degree CMB anisotropies, at z~1000, to anything at present epoch, z~0? CMB anisotropies are astronomically large (one degree); at present epoch, they would be about 1Gly across.

[ajb]

Cosmic strings & inflation are speculations, yes?

 

I would say that inflation is well established now. The evidence is in the details of the CMBR. As for cosmic strings, I am not aware of any direct evidence.

 

 

No observations connect one-degree CMB anisotropies, at z~1000, to anything at present epoch, z~0?

 

I am not familiar with any work relating the anisotropies with actual structures at the present epoch.

[Widdekind]

I would say that inflation is well established now. The evidence is in the details of the CMBR. As for cosmic strings, I am not aware of any direct evidence.

 

 

 

 

I am not familiar with any work relating the anisotropies with actual structures at the present epoch.

i understand, that the anisotropies are enormous (bigger than our sun or moon on our sky), and would correspond today to volumes ~Gly across. Meanwhile, during the epoch of "reionization" (z ~ (30-6)), stars formed in globular star cluster massed clumps, on size scales over 6 decades smaller. Then, during the Quasar & star-burst era (z ~ (6-1)), the largest of those star clusters (~10⁸M_sun) formed central IMBH, and "grew" into galaxies, by further "secondary" star formation. If so, then the "seeds" of structure were over 6 decades smaller, than the CMB fluctuations -- which, again, are larger than the size scale beyond which our universe is already considered uniform, isotropic, homogenous. i understand that current cosmology computer simulations still do not span such a dynamic range.

 

i want to understand why inflation is "well established" -- if humans cannot in principle observe back before (z ~ 1000); then how have humans confirmed inflation at (z ~ infinity) ?

[ajb]

i want to understand why inflation is "well established" -- if humans cannot in principle observe back before (z ~ 1000); then how have humans confirmed inflation at (z ~ infinity) ?

 

The short answer is that the details of the CMB angular power spectrum agree with what is predicted by inflation.

[IM Egdall]

Inflation theory explains observations which the standard big bang theory cannot:

 

1) The extremely high uniformity of the observable universe

 

2) The overall flat spacetime curvature of the obsevable universe.

 

3) the lack of magnetic monopoles.

 

 

See link - http://map.gsfc.nasa.gov/universe/bb_cosmo_infl.html

[Widdekind]

If you ponder a flat, matter-dominated (matter-only) universe; then the proper distance to the visible edge of our universe asymptotes to 2c/H₀ ~ 27Gly ~ 30Gly. And then, the one-degree CMB anisotropies represent structures which were (z~1000) about (1/60 radian) x 30Gly / (1+z) ~ 0.5Mly across; and which hypothetically are expanded to a size ~0.5Gly at present epoch (z~0), ignoring gravitational collapse. That is quite close to the ~100Mpc scale of cosmic uniformity. And there are two smaller, secondary anisotropies, at scales of a third & a quarter degree. And more, our universe is plausibly (slightly) closed; a closed cosmology would dilate distant objects larger on our skies. So a combination of "matter only" and "closed curvature" could translate directly-observed one-degree anisotropies, into smaller physical size scales, at and below the directly-observed scale of cosmic uniformity. Guided by the following figure, which maps out space within 100Mly of earth, i.e. is 200Mly across; CMB anisotropies could plausibly correspond to large galaxy super-clusters, e.g. Eridanus/Fornax, Virgo; and, oppositely, Voids:

Speculating, that "matter only" + "closed curvature" + "CMB anisotropies became super-clusters & Voids" seems common-sensical & parsimonious.

 

EDIT: The following figure, mapping space out 1Gly, seemingly shows anisotropy (Voids & Super-Clusters) on scales of ~100Mpc. Perhaps the following figure can be directly correlated to CMB one-degree anisotropies?

Edited November 17, 2012 by Widdekind