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When space and time began

  1. Apr 26, 2015 #1
    what was space and time before the big bang thank you
  2. jcsd
  3. Apr 26, 2015 #2


    Staff: Mentor

    The short answer is we don't know because when trying to extrapolate the laws of physics past that point we run into a singularity that prevent us from going further.

  4. Apr 26, 2015 #3


    User Avatar
    Science Advisor
    Gold Member
    Dearly Missed

    There are some reasonable guesses and they have to be tested to see which fits new data better.
    Here is one proposal which I like. It seems to fit the existing data, collected so far.
    Google "LambdaCDM bounce"
    The title refers to the standard cosmic model "Lambda Cold Dark Matter" which is the main model currently in use. The authors explore in some detail what results if you run that model in a collapse according to knows physical laws, and then allow it to bounce according to conjectured quantum effects that have been studied quite a bit but not yet proven.
    A ΛCDM bounce scenario
    Yi-Fu Cai, Edward Wilson-Ewing
    (Submitted on 9 Dec 2014)
    We study a contracting universe composed of cold dark matter and radiation, and with a positive cosmological constant. As is well known from standard cosmological perturbation theory, under the assumption of initial quantum vacuum fluctuations the Fourier modes of the comoving curvature perturbation that exit the (sound) Hubble radius in such a contracting universe at a time of matter-domination will be nearly scale-invariant. Furthermore, the modes that exit the (sound) Hubble radius when the effective equation of state is slightly negative due to the cosmological constant will have a slight red tilt, in agreement with observations. We assume that loop quantum cosmology captures the correct high-curvature dynamics of the space-time, and this ensures that the big-bang singularity is resolved and is replaced by a bounce. We calculate the evolution of the perturbations through the bounce and find that they remain nearly scale-invariant. We also show that the amplitude of the scalar perturbations in this cosmology depends on a combination of the sound speed of cold dark matter, the Hubble rate in the contracting branch at the time of equality of the energy densities of cold dark matter and radiation, and the curvature scale that the loop quantum cosmology bounce occurs at. Importantly, as this scenario predicts a positive running of the scalar index, observations can potentially differentiate between it and inflationary models. Finally, for a small sound speed of cold dark matter, this scenario predicts a small tensor-to-scalar ratio.
    14 pages, 8 figures.
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