Re: Does inflation theory imply a (slightly) closed universe?

Dear Rob,

The short answer to your question is that the density of the universe is still up in the air. The long answer can be summarized in a few points:

1) the flatness and homogeneity problems suggest that something like inflation took place. Inflation in its simple forms results in a universe precisely balanced between open and closed: Omega=1.0 to many significant places (20+ ?) Of course theorists are clever! Thus more complicated models of inflation (sometime involving multiple fields) can yield either open of closed universes depending on the details. These are not particulary generic models though and I think it would be fair to say that inflation implies a flat (exactly) universe.

2) The *matter* density in the universe seems to be considerably less than required for closure. However, recent high redshift supernovae results suggest that the bulk of the density in the universe is made up of a cosmological constant. This may result in a total Omega=1. Note that this "dark energy" is not the same as the "dark matter" which is already included in the matter density mentioned above.

3) However, if the cosmological constant is truly non-zero then the universe is fated to expand forever and indeed accelerate. Essentially, the universe may re-enter a phase of inflation, perhaps forever this time. Note that the supernovae results are still pretty uncertain at this time and that we really don't know for certain.

I hope this helps to answer your question.

-- Geza Gyuk