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X-ray background/peculiar velocities and the Big Bang

  1. Jun 20, 2007 #1
    I heard that the X-ray background and peculiar velocities provide evidence that leads scientists to believe in the Big Bang model. What exactly do they have to do with it?
  2. jcsd
  3. Jun 20, 2007 #2


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    The backgound is not x-ray, but microwave. According to theory about 300,000 yrs. after big bang, the universe was cool enough for atmos to form. The universe was filled with radiation at a high temperature. As the universe expanded, the radiation cooled down to its present value (slightly under 3 deg. K). There doesn't seem to be any other explanation.

    The velocities that you refer to are those of galaxies which are going away from us with speed proportional to distance - characteristic of an expanding universe, which started a little less than 14 bil. yrs ago.
  4. Jun 21, 2007 #3


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    There is actually a x-ray background that is diffuse at large scales, but that can be resolved in individual sources when observing with high angular resolution. The background is assumed to be the result of individual sources at high redshifts. There are however lots of unanswered questions regarding the x-ray background such as its relation to structure formation. I am not aware how this background can be used to discriminate between cosmological models.

    On the other hand, statistical analysis of peculiar velocities can be a test of cosmological models or at least classes of models. This is because the model-dependent spectrum of perturbations determines the conditions for non-linear gravitational collapse and how structure is formed. Thus for example a cold dark matter model with a hierarchical bottom-up structure formation history predicts high peculiar velocities due to collisions and tidal forces.
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