On 7/18/2025 5:18 PM, Alan Grayson wrote:
On Friday, July 18, 2025 at 5:04:35 PM UTC-6 Brent Meeker wrote:
On 7/18/2025 4:10 AM, John Clark wrote:
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.*
Good, except there is also a small component due to the higher
mass density in the universe in the distant past which also adds
to the redshift relative to us. And while "the more distant it is
the larger it's redshift" is true, the relation is not linear as
encoded in a Hubble constant. That's where talk of accelerated
expansion comes from.
Brent
Generally speaking I still don't get it. What I do get is that since
the Earth isn't the center of the universe, the red shift observed
cannot be due to relative motion in space, but to the expansion of the
universe.
It's all relative motion in space. But only the part due to the
expansion of the universe is significant; so forget the local proper motion.
HOWEVER, Clark (and you?) agrees that the observations correspond to
behavior in the distant past,
I don't know what that means. Galaxies are observed at all different
distances and corresponding different times in the past. Then it is a
curve fitting problem to say what universe model best fits the data.
and the further back in time we go via Hubble, the red shift
increases, implying increasing recessional velocity.
Yes, things further away have a higher redshift. We have a higher
recessional velocity relative to them.
If that's the case, why does Clark (and you?) claim that in the very
early universe, the galaxies were receding from each other slowly,
presumably much slowly than today? AG
Look at the curves I posted. Most of them, but not all, show a lower
Hubble parameter, less slope, earlier.
Brent
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