From: Anders Sandberg (asa@nada.kth.se)
Date: Thu Aug 15 2002 - 14:35:12 MDT
On Thu, Aug 15, 2002 at 09:22:42PM +0200, Joao Magalhaes wrote:
> I don't get it. Why do you say the universe doesn't have a center? I mean,
> if you could determine the positions of all galaxies then you could find
> the center.
If you do that, you will find that the center is... here! The universe
looks roughly the same in all directions and is homogeneous everywhere on
the large scale. There is no huge central void or strange omphalos
marking the center, just galaxies everywhere moving away from each other.
It is a bit like asking where on the surface of the Earth the world's
center lies. In the case of the universe, one could perhaps say the real
center is not so much a place as an event - the Big Bang itself.
> Also on the same subject, can you determine the direction
> galaxies are moving to in a 3D axis? If you know the direction a galaxy
> going, you can determine where it came from. Right? I imagine relativity
> should play a role here too, but I just don't know what it is, so I suspect
> there are several flaws in this paragraph.
The radial part of velocity (towards/away) from us can be determined by
looking at their redshift - the light becomes redder if it is moving away
and bluer if it approaches, and by looking at where spectral lines in the
light end up you can determine the velocity fairly exactly.
The tangential part (sideways) is harder. I honestly don't know how
astronomers measure it for galaxies.
-- ----------------------------------------------------------------------- Anders Sandberg Towards Ascension! asa@nada.kth.se http://www.nada.kth.se/~asa/ GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y
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