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

Wiltshire casts doubt on existence of dark energy

  1. May 8, 2007 #1


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    Wiltshire casts doubt on existence of "dark energy"

    Wiltshire is a minority voice in cosmology, but one worth listening to. Speculation about a "dark energy particle" would be in vain if the appearance of acceleration can be traced to classic GR effects, which is what he tries to do. Wiltshire suggests that a positive cosmological constant is NOT NEEDED to explain observation, nor is any sort of dark energy or quintessence.
    This bears on the discussion of various approaches to quantum gravity, which have differing compatibility with the cosmological constant

    Cosmic clocks, cosmic variance and cosmic averages
    David L. Wiltshire
    72 pages, 5 figures

    "Cosmic acceleration is explained quantitatively, purely in general relativity, as an apparent effect due to quasilocal gravitational energy differences that arise in the decoupling of bound systems from the global expansion of the universe. 'Dark energy' is recognised as a misidentification of those aspects of gravitational energy which by virtue of the equivalence principle cannot be localised, namely gradients in the energy associated with the expansion of space and spatial curvature variations in an inhomogeneous universe, as we observe. Gravitational energy differences between observers in bound systems, such as galaxies, and volume-averaged comoving locations within voids in freely expanding space can be so large that the time dilation between the two significantly affects the parameters of any effective homogeneous isotropic model one fits to the universe. A new approach to cosmological averaging is presented, which implicitly solves the Sandage-de Vaucouleurs paradox. When combined with a nonlinear scheme for cosmological evolution with back-reaction via the Buchert equations, a new observationally viable quantitative model of the universe is obtained. The expansion age is increased, allowing more time for structure formation. The baryon density fraction obtained from primordial nucleosynthesis bounds can be significantly larger, yet consistent with primordial lithium abundance measurements. The angular scale of the first Doppler peak in the CMB anisotropy spectrum fits the new model despite an average negative spatial curvature at late epochs, resolving the anomaly associated with ellipticity in the CMB anisotropies. A number of other testable consequences are discussed, with the potential to profoundly change the whole of theoretical and observational cosmology."
    Last edited: May 8, 2007
  2. jcsd
  3. May 8, 2007 #2


    User Avatar
    Science Advisor
    Gold Member

    Does the equivalance principle insist gravitational energy cannot be localized? I don't really follow that part of the argument. Gravity appears localized on the scale of our solar system, and probably the Milky Way. I am suspicious of effects that are not locally evident.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook