John Kierein (from another thread): I guess MAP refers to Microwave Anisotropy. The BBT predicted anisotropy of 1 part in a 1,000, but it's 1/100,000. This anisotropy is in better agreement with absorption of the background by distant galaxies in a static universe than it is with a big bang.

"MAP" stands for "Microwave Anisotropy Probe". Launched in June 2001, MAP reached the L2 point in October 2001 and began observations. As of April 1, 2002, it has already completed observations for one full sky map. MAP is more sensitve than was COBE, and can study anisotropies at much higher angular resolution. Other anisotropy experiments, such as BOOMERANG, MAXIMA, DASI and the Very Small Array are able to observe at high angular resolution, but can only see small parts of the sky. Planck, a European Space Agency mission, is now scheduled for launch sometime in 2007, a serious slip from the planned 2003. Like MAP, PLANCK will measure the CMB at high angular resolution on the whole sky. However, PLANCK will be the first CMB mission able to measure polarization as well. Theory suggests that there should be a polarization signature from gravitational waves in the early universe, superimposed on the anisotropy patches in an all sky map. PLANCK may be able to see that signature, although it will be just about at the limit of detectability.

The claim that BBT predicts "anisotropy of 1 part in a 1,000" cannot possibly be true. There are no fixed parameters in BBT from which one could compute a necessarily a-priori anisotropy amplitude. At best, such a computation could only reflect the bias of the theorist who made it, and not the theory behind it.

The proper treatment of the anisotropy spectrum is to measure it, and fit the measurement as best you can, to a small number of free parameters in the theory (matter & energy densities, cosmological constant, Hubble constant,age of the universe, and etc.). The truth is that the anisotropy angular power spectrum, and BBT are very much compatible with each other. There is a very good online tutorial that describes how cosmological parameters can be extracted from the anisotropies in the CMB, "Introduction to CMB Anisotropies", by Wayne Hu of the University of Chicago. It is well written, I think, for nonscientists, but it is long. Wayne Hu also has another page, "An Introduction to the Cosmic Microwave Background", a more general introduction that does not deal in detail with the anisotropies. Also see Max Tegmark's Homepage (University of Pennsylvania). He is one of the more active theorists studying the anisotropies in the CMB, and there is much good stuff here too.

While is is in fact obvious that BBT and the CMB anisotrpies are very much compatible with each other, it is by no means obvious that one can say the same for a cosmology built around the Compton redshift hypothesis. Compton scattering is already accouned for in the Sunyaev-Zeldovich Effect (SZE). The SZE is well studied, and is known now to produce perturbations on scales far below those actually seen. This would naturally lead one to believe that BBT is a much better match to all apsects of the CMB than a Compton effect cosmology could be. Also see The Sunyaev-Zeldovich effect in CMB-calibrated theories applied to the Cosmic Background Imager anisotropy power at l > 2000, J.R. Bond et al., 23 May 2002, submitted to Astrophysical Journal (the Cosmic Background Imager is yet another of the many high resolution, post COBE, ground based CMB experiments).

One other observation. It is noteworthy that the many ground based & balloon borne CMB experiments active today all return essentially the same angular power spectrum, despite observing different patches of the sky. One would expect this from BBT, where there is a causal connection in the early universe. It does not seem evident to me that a Compton effect cosmology would necessarily be expected to return the same results, since there should be no causal connection between remote parts of the sky.

<font size=-1>[ This Message was edited by: Tim Thompson on 2002-06-07 17:01 ]</font>

I don't know the details, but I believe that the evenness of the background radiation *is* a logical consequence of the Big Bang.

The fact that it is much *more* even than expected is one of the details that the "expansionary phase" BBT explains very nicely.

Silas

Correction

I need to correct what I said about the Sunyaev Zeldovich Effect (SZE). The temperature fluctuations cause by SZE are in fact larger than I thought, and larger than what you would expect from a straight BBT. So Kierein is partly correct, in that Compton scattering will produce a larger delta-T/T fluctuation than one would expect from any BBT (where "delta-T/T" means temperature increment (delta-T) divided by temperature (T)).

However, the Compton scattering SZE can be distinguished from the BBT CMB and removed from it. The reason is that it skews the spectrum to make it slightly non-thermal, and the effect is to lower the apparent temperature for frequencies below 200 GHz (1.5 mm wavelength), and raise it for higher frequencies. Removing the Compton scattering skew leaves only a pure BBT effect behind.

It also remains that the angular power spectrum of the CMB anisotropies is consistent with BBT. It also remains that the consistency of the angular power spectrum across the whole sky cannot be accounted for by Compton scattering, but must be explained by an underlying structure. That structure comes naturally out of BBT because of the primordial causal connections.

As Silas suggests, inflationary cosmology is a modification over original BBT scenarios, whereby large scale structure in the current universe comes about by the rapid expansion of primordial quantum structure.

<font size=-1>[ This Message was edited by: Tim Thompson on 2002-06-07 19:59 ]</font>

Depending on how one views the data, the fundamental problem of viewing CMB lies in our ability to see the whole picture. An observer can only see a part of the universe, and must speculate about the rest. The universe would come to an end probably before the observer could view the whole thing.

So, assertions that the CMB is nicely distributed are true only for the area of space that we can see.

I tend to agree with Hawking that the proper solution for expansion of the universe could be as follows: maximum radius of euclidean 4-sphere is sqrt (3 / A), and the minimum radius of Lorentzian space is the same. As such, you would have half the euclidean solution joined to half the Lorentzian solution. This brings up an interesting viewing of the universe, because what we may actually be seing in the CMB is the remanant of a shockwave when the Euclidean/Lorentzian transition took place. And of course, that brings into question whether the universe is still smooth in it's Lorentzian expansion, or have irregularities formed through galaxy creation and interaction?

I agree that a lot more research needs to be done, and certainly we will get some very interesting results from the satellite studies. However I think a more fundamental problem may exist.

DJ

<font size=-1>[ This Message was edited by: DJ on 2002-06-07 20:12 ]</font>