fishing net

[Boud Roukema]

Cze¶æ wszystkim,
   It's a nice analogy :).

Of course, just like nearly any analogy, this one is not perfect.

As Micha³ said, it's true that the deviations from homogeneity are
small on scales anything much bigger than the Schwarzschild horizon of
a SMBH   http://adjani.astro.uni.torun.pl:9673/zwicky/SuperMBH

Another problem is that in the 2D balloon, the positive fluctuations
(the net) are connected in a continuous network, while the negative
fluctuations (lowest density) are unconnected, separated from one
another.

In the standard (3D) model, at early times the + and - fluctuations
are typically of the same typical sizes (e.g. from the hypothesis of
"gaussian fluctuations"), and the 2D topology of contours of constant
density ("genus analysis") is connected both for + and - fluctns.

If you consider all matter more dense than some value,
- a low density value gives a "gruyere (ser) topology"
- a critical density values gives a "sponge topology"
- a high density gives a "meatball topology"

This is impossible to do with a balloon, which is 2D, since the
topology of constant density "1-surfaces" is 1D.

But I still like the analogy, because it gives a feeling of the
constraint caused by positive matter density.

na razie
boud


On Fri, 6 Dec 2002, Michal Frackowiak wrote:

> szajtan odwieczny wrote:
>
> > hello everybody. Got an idea to share.
> > Once upon a time I thought about such a thing.
> >
> > What was observed are the great voids (of size about 100 Mly in
> > diameter or even bigger) separated by some cosmic great scale
> > structures so it altogether looks like a soap foam. Assuming that the
> > voids are empty, than the curvature of out local part of the
> > Universe would look like - example in 2d: as we were pumping the
> > balloon but confined by a fishing net which doesn't allow the surface
> > of the balloon for free expansion, and in the end the balloon is
> > quizzed by the strings of the net but it out stands in the holes of
> > the net between the strings. In 3d this would be little more
> > complicated to imagine but what do you thing about this ?
> >
>
> that is correct. curvature is constant only in homogeneous universe. in
> the perturbed one it is not. but deviations are really small.
> good luck
> michal
>
>