Darren New nous apporta ses lumieres en ce 2008/01/02 21:48:
> Warp wrote:
>>   Galaxies do not expand because their gravity keeps them in shape. In
>> other words, gravity inside (and near) galaxies is strong enough to
>> "resist" the expansion. Consequently nothing inside galaxies expands.
> 
> Hmmmm.... I'll take this idea with a grain of salt. :-)
> 
>>   Another slightly difficult thing to grasp is that a constant expansion
>> of the universe actually means that galaxies recede from us at an 
>> exponential
>> rate. At each certain unit of time space distances double, which means 
>> that
>> the distance between two galaxies grows exponentially with time. 
> 
> Yet, funny enough, the number of galaxies we see in an area is constant 
> for a given volume, or close to it. This implies that perhaps the 
> galaxies aren't receding at all, and space isn't growing at all.
It is NOT constant! There are several regions in space that don't have any 
galaxies for 100's of millions of light-years in any direction, and some where 
galaxies are clustered toggether with average distances around a few 10000's 
light-years. Our galaxy is around 27000 light years across.
You have galaxies clusters, then super clusters and mega clusters. You have 
galaxies "filaments", literaly very long strings of galaxies and galaxies 
clusters stretching for billions of light-years.
> 
> I saw an interesting paper that postulated that what we observe would 
> also be correct if further galaxies simply had a time axis pointing away 
> from us. I.e., plot the universe on the surface of a sphere, and have 
> time running perpendicular to the surface. The further apart two points 
> are, the more red-shifted they will see each other, even if the sphere 
> isn't expanding. It explains why we see a constant number of galaxies in 
> a given space, and a number of other problems as well (like the "dark 
> energy" expansion effect). It also explains the background radiation, 
> the fact that it's flat everywhere, and that
Once again, the background radiation is realy not constant at all. It contains 
both small scale and large scale "textures" with intensity variations of around 
1 to 100.
> 
> I'm eager to hear about it coming out in a peer-reviewed journal.
> 
>>   Dark energy has been postulated as an explanation for this. It somehow
>> causes an inflationary effect on the universe, making it to expand in an
>> accelerated way.
> 
> Sounds ad hoc to me. :-)  Fortunately, none of this affects my life in 
> even the most trivial way, until some scientist actually *does* 
> understand it well enough to make predictions and hence technology. :-)
> 
>>   (All this is not based on professional literature, so don't take it
>> for granted. It's just how I have understood it with me extremely limited
>> understanding.)
> 
> Understood. Thanks for the lay interpretation.
> 
It should be noted that some far galaxies are not receding fast enough and that 
others, closer ones, are receding to fast.

-- 
Alain
-------------------------------------------------
Stay out of my head, its a bad neighborhood.

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