TY. I think I get it, but I must devote more time to fully appreciate your comment. AG
On Friday, December 2, 2022 at 5:50:26 PM UTC-7 jessem wrote: > The wiki page on the Hubble parameter also says in the section at > https://en.wikipedia.org/wiki/Hubble%27s_law#Time-dependence_of_Hubble_parameter > > that the expansion seems to be accelerating in such a way that the first > derivative of the scale factor a(t) is increasing over time but the Hubble > parameter H(t) is decreasing, and that this has the implication "The > recession velocity of one chosen galaxy does increase, but different > galaxies passing a sphere of fixed radius cross the sphere more slowly at > later times". There's a more technical discussion of how these parameters > are defined at > https://en.wikipedia.org/wiki/Accelerating_expansion_of_the_universe#Technical_definition > > which mentions that physicists define "accelerating expansion" specifically > in terms of the second derivative of the scale factor being positive, it > doesn't require an increasing Hubble parameter. > > On Fri, Dec 2, 2022 at 4:15 AM Alan Grayson <[email protected]> wrote: > >> It's measured about 70 km/sec/megaparsec. This is a direct measurement >> using red shift to measure recessional velocity, and different standard >> candles depending on the distance. So, at a distance of one megaparsec, the >> expansion rate is 70 km/sec; at two megaparsecs the expansion rate is 140 >> km/sec; and so on. This suggests the rate of expansion is greater as we go >> back in time; or conversely, that the rate of expansion is slower as we go >> forward in time. How is this reconciled with the 1998 measurements that the >> rate of expansion is actually speeding up? AG >> >> -- >> 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/7eb0dfae-1e78-4917-942a-a1d89faf424cn%40googlegroups.com >> >> <https://groups.google.com/d/msgid/everything-list/7eb0dfae-1e78-4917-942a-a1d89faf424cn%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/1e8419ee-2366-4851-aab3-36d7d438ae36n%40googlegroups.com.
