Red shift and homogeneity

Google seems to be unable to show threads with more
than 250 posts so I'm reposting my reply to Jim as
a new thread at Jim's request. My apologies to those
of you who have seen it before.

George


"Jim Greenfield" wrote in message
om...

... I tried it myself on the good old graph paper, as follows:
I marked 10 x 10 boxes with 2 blanks between each marked box.
I then on page 2 repeated with 3 blanks- Expanded by 50% OK? (still
homogenous)

You have filled in some squares and left others blank, right?
If so the distance between the centres of filled squares has
increased from 3 units to 4 units or 33.3% but the approach
is fine. If you had marked dots at every second or third
intersection then it would be 50%.

I placed page 1 over page 2, and poked a pin through each spot.
Then I drew lines from each original position, to the expanded
position---- and put the razor away! Because without making a
selection, the expansion had shown by default all proceeding from the
center.(all lines point to it)

But you did make a selection ;-) I didn't se you do it but I
can make some guesses: Firstly, I guess you lined up the edges
of the paper. Secondly, when you had to match a square on one
sheet to the corresponding square representing the same cluster
of galaxies on the other sheet, I guess you selected the centre
square on one to correspond to the centre square on the other.

So somehow by making your red and green selections, and expanding from
them, you are (accidently) nominating those as the center, before
beginning.

Yes (deliberately), just as you (perhaps accidentally) nominated
the square at the centre of the paper to be the square at the
centre of the observable universe.

Now the essential feature of this demonstration is not that
you can find a single centre, it comes from comparing two
sets of lines made under different assumptions. You have
your first set but nothing to compare so now you need to
do the rest of the experiment. Get a different coloured pen
and draw another set of lines but this time assume that the
centre filled square on the first sheet corresponds to a
filled square about eight squares from the centre on the
second sheet, or, if you want to have the sheets represent
the observable universe, assume we are moving and offset one
sheet by eight squares when laying it over the other. It
might be harder to keep track of which squares to join but
I'm sure you can handle it.

Of course the green and red were still separating in my diagram, but
as I had expanded the whole (Universe) they were not at the indicated
center. Red and green would still exhibit red shift, but it would be a
vector of the real situation (if expansion was occuring)
So I am still leaning to the view that red shift and expansion are the
product of an intriguing illusion.
(For now take it that my 100 spots represent the entire 13.7 universe,
so taking a piece of it arbitrarily wont wash)

But the 13.7 (whatever) that we can see is already just
a tiny piece of the whole, an infinitesimal piece if the
universe is infinite.

I'm
afraid I am still stuck with the conclusion that if distant galaxies
are moving away faster than closer ones, then our (observed) universe
is getting less dense further out, and isotropy, but NOT homo can be
preserved under expansion.

Ned Wright: "To say that the universe is homogenous means that any
measurable property of the universe is the same every where".
(Which brings us back to that red shift cause, as expansion causes
lessening of density, and if galaxies further out are moving away
faster than those close to us, then there is a differential in density
occurring)

While you are looking at these sheets Jim, there is
something else you can do since they are nicely regular.
I want you to draw a square box roughly in the centre of
your first sheet 12 units on each edge. If I understand
your description there should be 16 filled squares inside.
Draw another box the same size at the centre of the second
sheet and there should be 9 filled squares inside. The
density (squares per box) has reduced to 9/16 of the
earlier value (in 3D it would have reduced by 27/128). The
lines should show that 7 squares have moved outside but
the 9 remaining were previously inside.

Now try that at the edge of the paper with the same size
of boxes. You should find the same change in density but
this time (depending on the size of the paper) most of
the 16 original squares will have 'moved' out of the box
to be replaced by 9 new squares that have moved in. The
clusters represented by these squares are moving quickly
out from your chosen centre but the density change is
identical. Now imagine your sheet was just a sample of a
whole sheet a billion miles on each edge. If you consider
two boxes the same size as those you have drawn but nearly
a billion miles away can you see the density before and
after would still be the same as at the centre? I hope
that illustrates that expansion maintains homogeneity.

That is the BB model but when you then take into account
the speed of light what we observe of course should be
squares with three blanks between nearby and only two
blanks between at greater distances. Other aspects make
it a difficult thing to measure though.

Jim, I may not be able to reply for a few days, we have
an exhibition that will tie us up until Sunday.

best regards
George