From: helbig@asclothestro.multivax.de
In article <88e77223-23b0-4bc7-aa2f-fab68bde22fe@googlegroups.com>,
Lawrence Crowell writes:
> > The universe appears to be approximately homogeneous on large enough
> > scales. Of course a single clump would violate this, but no-one is
> > proposing a single clump, nor a completely empty bubble. Rather, the
> > question is whether it is possible that inhomogeneities---within the
> > current observational constraints---can have observable effects and
> > perhaps explain some puzzling observations (though it is fair to say
> > that not all are puzzled by them).
>
> My immediate sense is no. The problem is the mass density of the
> universe is about 10^{-29}g/cm^3. It is difficult to seen how this with
> ordinary matter gives rise to the accelerated repulsion.
If there were no cosmological constant and the density were about
three-and-one-half times greater---still small by everyday
standards---it could lead to the collapse of the universe in the future.
Whether or not a quantity seems small by everyday standards is not
really relevant. Certainly the people who have investigated this are
aware of the average density of the universe.
> I wrote on
> Stack exchange how dark energy can be understood in part with Newtonian
> mechanics. It is not hard to understand how a homogeneous distribution
> of vacuum energy gives rise to accelerated expansion. The problem is
> understanding the quantum field theory giving rise to that dark energy.
>
> LC
>
> https://physics.stackexchange.com/questions/273888/can-a-photo
-have-a-wavelength-less-than-the-planck-length/273900#273900
Of course, it is an assumption that dark energy has something to do with
quantum field theory. Some or all of it might be due to other causes.
--- SoupGate-Win32 v1.05
* Origin: you cannot sedate... all the things you hate (1:229/2)
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