On Thu, Jul 17, 2025 at 9:59 PM Alan Grayson <[email protected]> wrote:
*> It seems to me that a red shift will be produced if an object is moving > away from us, regardless of the cause of its motion; that is, regardless of > whether space is expanding, or the object is moving away from us through > space. That's the red shift we observe,* *Yes.* * >and everyone seems to agree that is represents ancient history,* *Yes.* > *>what the relative motion was billions of years in the past. * *No, although astronomer sometimes speak imprecisely and people infer that the only way a redshift could be produced is by a thing moving through space away from us. I may have been guilty of such sloppy language myself from time to time.* *> So, even though the galaxies were much closer in spatial distance > billions of years ago, how can we NOT conclude that those galaxies were > receding from each other, AT THAT TIME, AT A HUGE RATE. represented by the > measured red shift? TY, AG* *A galaxy moving through space away from us is one way to produce a redshift, another way would be for the space between galaxys to be expanding, we can determine which one is actually causing the redshift through observation. Except for the Andromeda and Triangulum galaxies and about a dozen dwarf galaxies in our local group, every galaxy in the universe is displaying a redshift to us, and the more distant it is the larger it's redshift. If that redshift is caused by them moving through space away from us then the Earth is it a very special position, the center of the universe. However the idea that the universe contains anything as mundane as a center is problematic, and the Earth just happening to occupy that center is even more so.* *But if the redshift is caused buy the expansion of space itself then every observer in every galaxy would see the same thing that we do, except for a few very nearby ones, every galaxy in the universe would be displaying a redshift to them, and the more distant it is the larger it's redshift.* *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* dq? > > On Thursday, July 17, 2025 at 9:12:14 AM UTC-6 John Clark wrote: > > On Wed, Jul 16, 2025 at 11:52 PM Quentin Anciaux <[email protected]> > wrote: > > *> **Of course, the expansion of the universe was slower following > Inflation when the galaxies formed, starting around 380,000 years after the > BB,* > > > *Galaxies are a lot younger than that. Outside of the Cosmic Microwave > Background Radiation, the most distant object astronomers have ever > observed is a small but very bright galaxy called MoM‑z14, the James Webb > space telescope gave us a picture of that galaxy as it existed 290 million > years after the Big Bang. Although if we want a good picture of what that > galaxy looked like way back then we have to make some adjustments to the > raw data that James Webb gives us. By examining the spectrum we know that > most of the light that was emitted by MoM‑z14 was in the ultraviolet, > that's not surprising because most of the stars in it were large and very > hot, but today when we look at it we mostly see infrared light. Why? > Because thanks to the expansion of the universe MoM‑z14 has a HUGE red > shift of 14.44.* > > *> **but how can the red shift of distant galaxies NOT tell us about > their recessional velocity in the distant past, which is what Clark seems > to claim? He claims it only tells us how much the universe has expanded > since their formation when photon frequency shifted from UV to red.* > > > *In cosmology the term "recessional velocity" can be ambiguous because > there is a fundamental difference between X traveling through space away > from Y and the space between X and Y increasing; one is limited by the > speed of causality, a.k.a. the speed of light, but the other is not. 13.5 > billion years ago the amount of space between MoM‑z14 and the matter that > would one day form the Earth was much less than it is today, and during > that light's 13.5 billion year long journey to us space kept expanding, so > the wavelength of the light kept getting longer and redder. The amount of > space between the Earth and MoM‑z14** keeps getting larger, but that's > not because the galaxy was moving away from us through space, but because > the very space between it and us kept expanding.* > > > * > But distant galaxies are receding rapidly NOW? * > > > *"Now" is not a particularly useful word in cosmology. Nobody knows how > fast or in what direction MoM‑z14 is moving through space relative to the > Earth, and even if we did know I don't think anybody would find that number > would be very interesting because whatever it is it's negligible compared > to the huge amount of spatial expansion that has occurred since that light > was emitted. * > > *After compensating for the distortion caused by the huge redshift we can > form a pretty good picture of what MoM‑z14 looked like 13.5 billion years > ago, but we will NEVER get a picture of what it looks like in 2025, not > even if we wait 13.5 billion years for it, because long before that it's > red shift will become infinite and thus unobservable. There is a limit to > how fast two objects can move through space away from each other, but there > is no limit on how fast the amount of space between two objects can > increase. * > > -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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