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Originally Posted by Jeff Root
[Ken,
Why would "spatial gradients" necessarily be observed if the Big
Bang was an explosion?
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Because you would need them to explain the redshifts in that case-- were it an explosion, the redshifts would have to be
caused by said pressure gradients.
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Are measurments of the Universe's density
at different distances and in different directions precise enough to
reveal such gradients?
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It would be apparent in the CMB, not thee galaxy density, because the CMB is exquisitely smooth and dates back to the time when the universe was in thermodynamic equilibrium. During that phase, any kinetic energy gradients that gave rise to the CMB redshift in an explosion scenario would have to be generated by pressure gradients that would be clearly visible. Pressure is a scalar, so in order for it to have a gradient, it has to be bigger in one direction than the other-- unless one really believes that the Earth is at the center of the pressure peak.
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Also, Inflation was invented to explain the uniform temperature of
the CMBR. It should serve equally well to hide any spatial gradient
from our view.
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Yes, I agree inflation could do something to mimic this effect, but if you have inflation, it's already not an explosion! The issue was can you get the Big Bang model from an explosion scenario, and inflation, as an explosion, would violate special relativity.
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Do you have any other reasons for believing that the Big Bang was
not an explosion?
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Yes-- it's called general relativity. It's a good theory, and it would have to be totally wrong for the Big Bang to be an explosion, in addition to the observational problems with the explosion interpretation.