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Originally Posted by Ken G
Quote:
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Originally Posted by Jeff Root
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. |
Why? This is the first time I've seen an assertion to that
effect, and there is no obvious reason the pressure gradient
would have to be involved. Either way, explosion or not,
pressure gradient or none, the redshift appears to be a
combination of Doppler shift and gravitational redshift.
Quote:
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Originally Posted by Ken G
Quote:
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Originally Posted by Jeff Root
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 the 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. |
Why would they have to be clearly visible?
Maybe there was a large sphere of essentially uniform high
density expanding into a surrounding region of lesser density,
and all we can see is a portion of the high density region.
The pressure could also be essentially uniform within that
region. It would still expand into the lower pressure region
surrounding it.
If you have a spherical rubber balloon filled with air, and
compress it into a small volume, then release it, will there be
a pressure gradient within the balloon as it expands, or will
all the air be at essentially uniform pressure at any instant?
I think it will be at essentially uniform pressure.
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Originally Posted by Ken G
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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I certainly don't believe that we are at the center of such a
pressure peak, but I'm not aware of any evidence that we can't
be close to the center-- say, in the central 20%, 10%, or 5%.
Quote:
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Originally Posted by Ken G
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Originally Posted by Jeff Root
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! |
Yeah, it does seem to be a self-defeating argument. But if
you are going to posit an original expansion which has no
cause or explanation
and Inflation a miniscule fraction of an
attosecond later which also has no cause or explanation, but
serves to make the original expansion plausible, then I will
put some pressure on you!
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Originally Posted by Ken G
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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As it is, expansion does not violate special relativity simply
because the theory of expansion asserts that "space expands",
meaning that when stuff moves apart, you expand the coordinate
system to follow the stuff, instead of leaving the coordinate
system alone and letting the stuff move through it. You could
do the same thing with an explosion: Let the coordinate system
follow the stuff which is moving apart. Voila! No violation
of special relativity!
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Originally Posted by Ken G
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Originally Posted by Jeff Root
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, |
Why?
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Originally Posted by Ken G
in addition to the observational problems with the explosion
interpretation.
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Are you referring to something other than what you referred to
above? I asked for "other reasons". "Observational problems"
is extrordinarily vague. It isn't even clear whether or not
it is responsive to my request.
-- Jeff, in Minneapolis