Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

State of the universe address

  1. Oct 2, 2004 #1

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    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.
     
  2. jcsd
  3. Oct 2, 2004 #2
    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
     
  4. Oct 3, 2004 #3

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    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.
     
    Last edited: Oct 3, 2004
  5. Oct 3, 2004 #4

    Nereid

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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').
     
  6. Oct 3, 2004 #5
    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
     
  7. Oct 3, 2004 #6
    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.
     
  8. Oct 4, 2004 #7

    Chronos

    User Avatar
    Science Advisor
    Gold Member
    2015 Award

    Fred 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.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: State of the universe address
  1. The universe. (Replies: 19)

  2. The Universe (Replies: 15)

Loading...