How can that be?

Le 29/08/2014 10:35, Robert Miles a écrit :
So you're ignoring the possibility that they were closer together
before the universe expanded this much, and therefore such a collapse
would happen faster?

Yes, since ALL proponents of the "big bang" theory ALWAYS tell me that
the space expansion does NOT affect galactic structures and happens "in
the space between the galaxies".

Obviously Andromeda's disk is part of the galaxy...

Now, you seem to propose that the big bang affects galactic structures,
what is quite new.

Does this in your opinion also affect solar system structures?

Am I expanding too?

Le 29/08/2014 10:35, Robert Miles a écrit :

So you're ignoring the possibility that they were closer together
before the universe expanded this much, and therefore such a collapse
would happen faster?

After some hours of search I found this paper:
http://xxx.lanl.gov/pdf/astro-ph/9803097v1.pdf
Page 6 it calculates the acceleration due to the expansion agt 25O Kpc,
i.e. at scales comparable to the size of the ring (400 kpc) it arrives
at the conclusion that the influence of space expansion at this scales
is 11 orders of magnitude smaller than the gravitational attraction.
Even at cluster scales, the difference is 7 orders of magnitude.

From Ted Wright's pages
http://www.astro.ucla.edu/~wright/lerner_errors.html#SC

I gather that each 1.5 years the universe grows by 10%. Supposing that
each 1.5 Gy to the past it shrinks by 10%, the ring was 10% smaller
1.5Gy ago, i.e. 1.30E9 light years x 0.9 -- 1 170 000 000 ly, still
more than a million light years across.

3 Gy ago it was 1 053 000 000 ly, and 4.5 GY ago it was 947 700 000 ly
across. 1


12GY ago it should have been 559 607 373 ly years across, not a small
structure at ANY case!

I am quite sure that I have done a mistake somewhere of course, but you
should be able to correct me. I doubt that this would change a lot
anything. Speeds were smaller then also, the scale factor applies in
that sense too. Ted Wright says that if we have 1000 Km/sec (say) as a
galaxy speed, after 1.5 Gy will have 1100 km/sec and inversely 1.5 Gy
ago it would move with 900 Km/sec.

I do not think that space expansion can save you even if personally I do
not think that space is "expanding".

In article ,
jacob navia writes:
The collapse along one axis proceeds fairly
rapidly and kinetic energy is gained by the collapsing material in the
direction of the collapsing axis.

Obviously it will overshoot the central plane

That is "obvious" in the case of stars, which collide extremely
rarely. For _gas_, however, the story is different. Collapsing gas
collides in the central plane, forming a disk and ultimately stars
(in the case of a galactic collapse) or planets (in a stellar
collapse).

This will take a HUGE amount of time!

At first glance, it should take one free-fall time. Stellar collapse
apparently takes longer, but I'm not sure anyone understands why. If
you think galactic collapse takes longer than a free-fall time, I
think the burden of proof is on you to demonstrate that.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

Le 05/09/2014 16:45, Steve Willner a écrit :
That is "obvious" in the case of stars, which collide extremely
rarely. For_gas_, however, the story is different. Collapsing gas
collides in the central plane, forming a disk and ultimately stars
(in the case of a galactic collapse) or planets (in a stellar
collapse).

At the beginning of the collapse there is no central plane, we are
talking precisely about how this plane is formed, how it comes to exist.

So, your explanation could be reasonable for a collapse AFTER the plane
is well formed and contains enough gas and matter. At the start of the
collapse there is precisely no plane!

Then, we have a damped oscillation process that takes several
oscillations at least to build the initial part of the famous plane.

[Mod. note: no, gas falls into the plane *from both directions* and so
collides in the plane. Consider a sphere of gas with some angular
momentum --- mjh]

In article , jacob navia
writes:

Le 29/08/2014 10:35, Robert Miles a écrit :
So you're ignoring the possibility that they were closer together
before the universe expanded this much, and therefore such a collapse
would happen faster?

Yes, since ALL proponents of the "big bang" theory ALWAYS tell me that
the space expansion does NOT affect galactic structures and happens "in
the space between the galaxies".

The expansion of the universe does not apply to bound structures; that
is correct.* The precursors of bound structures now were not always
bound in the past, however. (This is obvious when one thinks about it.)

Obviously Andromeda's disk is part of the galaxy...

Now, you seem to propose that the big bang affects galactic structures,
what is quite new.

Does this in your opinion also affect solar system structures?

Am I expanding too?

Brooklyn is not expanding. :-)

*For all practical purposes this is true. The actual situation is a bit
more complicated. While it is true that bound structures do not take
part in the expansion of the universe (so neither you, nor Brooklyn, nor
Woody Allen, nor the Solar System, nor atoms are expanding), their
size (which is determined by some sort of equilibrium in all cases) can
be slightly different to the case of no expansion. There is a paper by
Davis and Lineweaver on this.

On Sun, 07 Sep 14, Phillip Helbig wrote:
their size (which is determined by some sort of equilibrium in all cases)
can be slightly different to the case of no expansion. There is a paper
by Davis and Lineweaver on this.

Ah, the vagaries of scale, which I think you're alluding to. A large
mathematical sphere has a smaller ratio of surface area to volume,
compared with a smaller sphere. This seems to be their only
difference, and so "scale" depends on some kind of invariant unit.

Given that, what if the difference between past epochs and the present
were not that the universe is physically expanding, but just that the
invariant unit of "scale" has been shrinking. That would cause the
redshift, would it not.