On Wednesday, July 23, 2025 at 4:44:08 AM UTC-6 John Clark wrote:
On Tue, Jul 22, 2025 at 3:53 PM Alan Grayson <[email protected]> wrote: *>I think I get it. Although light from ancient galaxies left those galaxies in the distant past, the red shift we observe reflects the expansion of the cosmos since then, and represents their recessional velocity at this time, NOW. This is consistent with Hubble's law, which tells us how fast galaxies outside the local group are receding in real time, NOW. AG * *Yes, but you have to be careful with "recessional velocity" because in cosmology the term can be ambiguous; sometimes it means how fast an object is moving away from us through space, and sometimes it means how fast the space between us and the object is expanding. I think cosmologists should have two different words for those two different things but unfortunately they don't. * *John K Clark See what's on my new list at Extropoli <https://groups.google.com/g/extropolis>s* Now I'm not sure I understand this. If we observe large red shifts from distant galaxies, how can we be sure most, or all of it is the result of spatial expansion, and not relative motion early on? Also, how can the red shift indicate recessional velocity NOW? Suppose the universe suddenly stopped expanding. Wouldn't we have to wait billions of years to observe that? It couldn't be observed NOW. 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 visit https://groups.google.com/d/msgid/everything-list/68667eb0-01db-4884-a178-7b86108e08ffn%40googlegroups.com.
