🚀 go-pugleaf

 I saw some people suggesting that the existence of
matter in the universe would cause the expansion-rate
to slow down _because of mutual gravitational attraction_

Of course, if one reads `gravitational attraction' as
an interpretation of the mathematical solutions of
Einstein's global scale equations (where the stress-
energy tensor is idealized as that of an ideal fluid),
then the assertion is correct, albeit somewhat
meaningless (just giving _names- ).

If one however reads this `mutual gravitational attraction'
in an intuitive `Newtonian' sense, then the assertion
is false, of course: the supposed homogeneity of the
universe implies namely precisely that the mutual attraction
is zero (in one point, the net contribution of gravitation
of other points is zero due to isotropy).

Therefore, in the Newtonian sense, one would expect the
expansion-rate to be constant, regardless the amount of
matter in the universe. Now Einstein's equations say
differently, but it should be remembered that their
global scale application is based on the somewhat thin
assumption that the global matter-distribution can be
idealized as that of a perfect fluid.

If one would for instance idealize the stress-energy
tensor as that of some discrete lattice (with matter-
concentration in the lattice-points), then Einstein's
equations would confirm the Newtonian expectation.

Advantages: no more `missing matter' (or abundance
of matter) problems, and agreement with observations,
which favour a universe expanding with constant rate.

marc van loo.
scip1061@nuscc.nus.sg  (university of singapore).