cosmic background radiation - alternative proposal


by zforgetaboutit
Tags: alternative, background, cosmic, proposal, radiation
Nereid
Nereid is offline
#55
Sep7-04, 09:23 AM
Emeritus
Sci Advisor
PF Gold
P: 4,005
Quote Quote by zforgetaboutit
My motives are being misunderstood.

How about if you reconsider my postings as "Has anybody studied or proposed... (zforgetaboutit's musings)?"

When a prof suggests a research topic to the grad student, the grad student doesn't (usually) say "First you prove it then I'll consider it." or "That can't be right because nodbody else has published it."

Most of what I'm suggesting are directions in research for those who have the means to go down that road.

For no good reason one of the replies (not yours) was downright hostile.

I continue...
Oops, sorry!

Yes, I did misunderstand; the context of the sections here at PF has changed somewhat in the last month or so ... your good questions (if I may paraphrase, 'why is the CMBR considered to be a relict of the Big Bang? what foreground explanations have been ruled out and why?') deserve clear answers. If I may so however, sometimes I didn't fully understand some of those questions, rather interpreted some of them as "I've got an alternative proposal for the nature of the CMBR, it's {X}".

So, in a nutshell:
- AFAIK, no proposal other than that the CMBR is a highly redshifted 'image' of the surface of last scattering is consistent with the high quality observational data
- there are several well-understood foregrounds: the 'red tail' of thermal radiation from the solar system zodiacal light, 'free-free' emission, emission by (MW) galactic dust (both rotation - 'spinning' - and vibration), synchrotron emission, point sources (mostly beyond the MW), and the Suyaev-Zel'dovich effect (SZE)
- there are also some 'cosmological' footprints that are not 'just' the surface of last scattering, e.g. gravitational lensing of the CMBR, the late integrated Sachs-Wolfe effect, the Ostriker-Vishniac effect (aka 'the kinematic SZE'), and patchy re-ionisation
- AFAIK, all the 'well-understood' foregrounds have been unambiguously detected and well-characterised
- the Tegmark paper you provided a link to has a good discussion of each of these, as well as references to papers examining each in much more detail.

The SZE is a very interesting thing! I will do some digging to find what the status of the observational validation, in the microwave region. You will see there's an implication of the SZE for high energy cosmic rays - the inverse Compton scattering which give the microwave SZE footprint also produces high energy gammas (as also happens in supernova shockfronts) - in a few years' time (when CANGAROO and HESSI and VERITAS accumulate good data), and maybe after GLAST has been at work for a while, there should be independent data on the (distant) CMBR ... via UHE gammas!
Nereid
Nereid is offline
#56
Sep7-04, 09:40 AM
Emeritus
Sci Advisor
PF Gold
P: 4,005
This set of slides from COBE give a nice overview of how COBE worked, how foregrounds were measured and subtracted (and what they were), what the dipole is, etc.

Note that the microKelvin fluctuations detected by COBE may not all be 'real' - at that level the researchers could only be sure that there *were* statistically significant fluctuations in the (dipole-removed) residuals, of approximately the size and nature predicted by the [tex]\Lambda[/tex]CDM cosmological models. The later CMBR observations - MAXIMA, DASI, ACBAR, CBI, FIRS, BOOMERANG, WMAP - were of higher precision, so any particular fluctuation has now be clearly re-observed (usual caveats apply, e.g. angular resolution).


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