State of the universe address

[Chronos]

If interested in a current overview of the standard cosmological model try
http://arxiv.org/abs/astro-ph/0409280
This paper gives a mix of both the conceptual and technical foundations of modern theory and addresses a number of hot issues that remain unsolved. A good read for all levels of expertise.

[meteor]

I didn't know the empirical Hubble law (equation 10):
z=H*L
where L is luminosity distance
although i knew the more familiar Hubble law
v=H*d

[Chronos]

I didnt't know that either. It was quite interesting. One thing I found particularly interesting was the discussion on how DM broke free from the early universe and facilitated structure formation in the early universe. I have often been uneasy with dark matter, but, that makes a pretty compelling case for it.

[Nereid]

I didn't know the empirical Hubble law (equation 10):
z=H*L
where L is luminosity distance
although i knew the more familiar Hubble law
v=H*dz, of course, is what you measure from the spectra of distant objects; converting it to a 'recession speed' is simple, and (AFAIK) in the early days papers gave a 'recession velocity' (z came later). L and d are more subtle - as Maroto and Ramírez point out, "neither the recession velocities nor the physical emission distances to galaxies are empirically measurable"; what we actually observe is an apparent magnitude (luminosity), and we convert to a 'distance' from an estimated absolute magnitude (the 'standard candle').

[meteor]

The section treating BBN is quite interesting. It has cleared me some doubts that i had about the deuterium bottleneck, and is always great to remember how Hoyle solved the puzzle of the production of heavy elements with his "triple alpha process". Hoyle was a great astrophysicist. I'm afraid that his involvement in the Steady State model has always been like a dark shadow over his career

[Mike2]

z, of course, is what you measure from the spectra of distant objects; converting it to a 'recession speed' is simple, and (AFAIK) in the early days papers gave a 'recession velocity' (z came later). L and d are more subtle - as Maroto and Ramírez point out, "neither the recession velocities nor the physical emission distances to galaxies are empirically measurable"; what we actually observe is an apparent magnitude (luminosity), and we convert to a 'distance' from an estimated absolute magnitude (the 'standard candle').
When they give the redshift as a function of the scale factor, is this the same as saying that early photons had to climb out of a deeper gravitational well because the universe was more dense back then? I'm not sure whether they are assuming a linear relationship between redshift and distance. Thanks.

[Chronos]

The section treating BBN is quite interesting. It has cleared me some doubts that i had about the deuterium bottleneck, and is always great to remember how Hoyle solved the puzzle of the production of heavy elements with his "triple alpha process". Hoyle was a great astrophysicist. I'm afraid that his involvement in the Steady State model has always been like a dark shadow over his careerFred Hoyle was a fine physicist. His attachment to the steady state model was quite reasonable given the observational evidence at the time. I never considered that a stain on his reputation.