On Wednesday, January 22, 2020 at 10:41:31 PM UTC-7, Brent wrote: > > > > 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..." >
Here's what Ned Wright says: *Is the Universe really infinite or just really big?* We have observations that say that the radius of curvature of the Universe is bigger than 70 billion light years. But the observations allow for either a positive or negative curvature, and this range includes the flat Universe with infinite radius of curvature. The negatively curved space is also infinite in volume even though it is curved. So we know empirically that the volume of the Universe is more than 20 times bigger than volume of the observable Universe. Since we can only look at small piece of an object that has a large radius of curvature, it looks flat. The simplest mathematical model for computing the observed properties of the Universe is then flat Euclidean space. This model is infinite, but what we know about the Universe is that it is really big <http://www.astro.ucla.edu/~wright/HGTTG.html>. > > *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 >> > -- > You received this message because you are subscribed to the Google Groups > "Everything List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected] <javascript:>. > To view this discussion on the web visit > https://groups.google.com/d/msgid/everything-list/86894144-8602-47ff-8d8b-30ce4a58dd6c%40googlegroups.com > > <https://groups.google.com/d/msgid/everything-list/86894144-8602-47ff-8d8b-30ce4a58dd6c%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/42c10d9b-ee63-4d47-8f24-540062ba7f10%40googlegroups.com.
