On 1/22/2020 8:18 PM, Alan Grayson wrote:
On Wednesday, January 22, 2020 at 8:51:50 PM UTC-7, Brent wrote:
On 1/22/2020 6:26 PM, Alan Grayson wrote:
On Wednesday, January 22, 2020 at 6:29:32 PM UTC-7, Brent wrote:
On 1/22/2020 5:08 PM, Alan Grayson wrote:
When you measure something and it is so close to zero
as to be indistinguishable from zero, then taking it
to be zero is not an assumption.
*Why don't you compare the measured value with the curvature
of a sphere 1 LY in diameter, or !0^6 LY in diameter? Do you
really think the curvature would be significantly different
from the measured value of the universe? I doubt it. So,
taking it to be zero, is just what you prefer, nothing more.
CMIIAW, AG*
No, because zero is a physically interesting value. There
maybe some unrecognized symmetry principle that makes it
zero. It's unlikely that there's some symmetry principle
that makes it 1e-6. That's why physicist look at the data as
evidence for zero. Of course they may be wrong. But it's
not because they are just pulling assumptions out of thin air.
Brent
*Why assume there's some symmetry principle to drive the
curvature to zero? *
You keep using the word "assume" which means to "take as given to
be true". Scientists hypothesize, they only "assume" for purposes
of testing the consequences.
*OK, then let's say when the measured value is close to zero, which
can't distinguish flat from spherical, cosmologists have a bias toward
saying it is flat. *
I don't know what "bias" would mean in that context. They don't say it
is flat. They hypothesize, consider, contemplate,...they say, "If is
flat, maybe it is because..."
*I don't mean they assume they're claiming "flat" is the Gospel. AG *
*It could be just because the universe is huge. *
Or it could be because some principle makes it zero. The latter
would be a more interesting discovery, so that's why cosmologists
consider it.
*They should consider everything of course -- I have no problem with
that -- but spherical implies finite, which you have to admit is
pretty amazing! AG *
*I don't think the cases are distinguishable by measurements.
OTOH, the article points to some measurements of the CMBR that
imply a spherical universe. Are they in any way persuasive? AG *
Nobody gets persuaded by one observation that contradicts the
prior observations. What if they had happened in reverse time
order...you'd be asking if the evidence for flatness is persuasive.
*OK, then taking all the points the authors raise, what probability
would you give that it's curved, not flat? I just want your sense of
the paper's main claim, or suggestion. AG
*
Their claim is they have new data that favors positive curvature over
zero or negative curvature to a significant degree (in the statistical
sense of significance).
Brent
*
*
Brent
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