Friday, December 9, 2011

change of redshift

it is planned to observe spectral lines of distant quasars with very high accuracy and see if their redshift changes with time. why does it change with time and would there be cosmological models where the redshift stays constant?


  1. the redshifts change with time because the recession velocities increase in all models except one: in an empty universe with curvature the acceleration is zero and the redshifts stay constant.

  2. This comment is not correct and should read:

    The redshifts change with time in all dynamical cosmological (FLRW) models, including an empty model with constant spatial curvature (this can easily be checked by calculation, e.g. for the Milne model). The related observable spectroscopic velocity shift (i.e., the observed spectral line displacement of quasars) changes with time accordingly, but in an empty universe with curvature the spectroscopic velocity shift vanishes, which reflects the fact that this model is not accelerating.
    References: The seminal paper by A. Loeb: arXiv:astro-ph/9802122
    arXiv:astro-ph/0105547, see Fig.6

  3. i've read the above comment a number of times and i seem to fail noticing the difference between my initial answer and the answer suggested by rhkail. so i do apologize for not being clearer in what i meant.