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
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