Re: The other direction


"N:dlzc D:aol T:com (dlzc)" <N: dlzc1 D:cox T:net@xxxxxxxxxx> wrote in
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Dear ajiko:

"ajiko" <ajiko2004@xxxxxxxxx> wrote in message
news:44225586$0$95986$742ec2ed@xxxxxxxxxxxxxxxxx
A recent lecture described the accounting of the matter in
the universe. It went something like this:

1) Ordinary mostly luminous matter in galaxies <X>
2) Dark matter surrounding galaxies <Y> (based on
velocity distribution of the stars).

Actually quite a quantity within the disk of spiral galaxies as well.
Notice also that they are now finding quite a number of "quiescent" black
holes at places other than the center of galaxies. These will also act
like centers of Dark Matter...

3) CBR indicating an overall flatness to the universe
that then implies a total amount of matter (using GR).
4) Leftover matter, about 80% must be somewhere.
Exotic matter theories sprout up.

It is considered that we are now capable of seeing all
the galaxies in the universe using the HST.

Not really. The most recent measurements indicate that inflation blew the
Universe up beyond our visible horizon, based on reporter's understandings
of what was said. Further expansion will have pushed even more over our
horizon.

This is used to determine the matter in (1) above. I don't understand
this. The sky is basically uniformly
covered with galaxies in all directions. To me this has
implications.

Pick the farthest galaxy we can see, say about 13
billion light years away.

Quasars, yes. Galaxies, I think only about 11 Gly away.

We see it forming as a quasar 13 billion years ago.
Imagine an astronomer in that galaxy 13 billion years
later looking out toward us. He will see our galaxy as
it is forming 13 billion years ago. What will he see if
he looks in the other direction? Can WE see any of
the galaxies he sees in that direction?

Possible, yes.

To me, it seems like the relative directions of motion
of all the galaxies are already basically determined
at the time the galaxies start to form.

Makes sense.

To me, it seems the energy-matter content of the
universe must continue on quite a long way beyond
that farthest visible galaxy.

This doesn't follow. It is entirely consistent with theory and
observation that spacetime is a product of the mass-energy in the
Universe, and that the total quantity of mass/energy is large but finite.
Does the value for c derive from the Universe at large?

We don't see the galaxies out there because they are not yet lit up -
not quite separated out into galaxies.

We have very little observation history to go on. There are some places
where new galaxies appear to be springing into existence, but there is a
large quantity of matter there that is as you say "unlit".

This cannot have been overlooked. So perhaps someone
can describe how GR can make the sky also look
uniformly distributed from the point of view of that
astronomer far, far away while not having an enormous
amount of additional energy or matter.

http://www.astro.ucla.edu/~wright/cosmo_01.htm

And since you asked:
"The laws of physics are the same for all inertial observers." This
couldn't be true in a Universe that didn't see about the same things we
see now, no matter where you did your observing from.

David A. Smith

Thank you for the thoughtful reply. The web page is quite helpful as well.

The following refers to the second diagram of part 4 from the web page you
pointed to.

If we considering the horizon image that is superimposed on the full
universe, then it appears that the full universe is 1000X or possibly much
more larger than our visible universe. Also, the rest of the universe would
be made up of much the same stuff that our visible universe is made of (at
least if we consider it at its matured age that the diagram's larger sphere
indicates).

The visualization of the universe as an expanding sphere is a long standing
technique. Do you know if that model is an actual GR solution? My
understanding is that the GR curvature cannot be modeled by simply embedding
it in a flat space with one more dimension. Also, the spherical model
implies a special connectedness nature. If it closes (as a sphere does), it
indicates finiteness. If it doesn't, then either it is finite with a fuzzy
edge somewhat like a galaxy has, or it is infinite.

The distribution of matter is not one of those fundamental laws of physics.
Rather it is an observational piece of data that helps to discover those
laws. What one sees in the sky is clearly NOT the same for all observers.
That far away astronomer is much closer to the stuff "the other side".

Ned Phipps


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