Final Cosmological Remarks

Did we answer any questions this term?

1. What is the age of the universe as determined from the observed expansion rate and cosmological distance scale? Is there a need to invoke the cosmological constant to reconcile the ages of the oldest stars with the value of the Hubble constant?

What is the nature of the large-scale distribution of matter in the universe as traced by the three-dimensional galaxy distribution?

Its a MESS!

And it is "filled" with Voids

What is the evidence for the existence of dark matter and what is its overall contribution to the total mass density of the Universe?

How did structure form in the Universe and what formation scenarios are consistent with the current observational data?

Where do the baryons reside? Are they predominately inside or outside of galaxies? How efficient was the process of galaxy formation? What is the true nature of the galaxy population? Do we have a representative survey of galaxies in the nearby universe from which coherent arguments about galaxy formation and evolution can be made?

If we can make this diagram 100 years after the first catalog of galaxies was made, then it means we still have a long way to go in determining the true space density of galaxies.

So it looks like most baryons are in potentials and these potentials are either defined by easy to detect galaxies, mostly invisible galaxies, or purely gaseous systems like QSO absorption line clouds.

Summary remark:

Cosmology in the mid 90's is substantially different than it was a mere 10 years ago. Hopefully the same rate of progress will be seen in the next 10 years.

My personal bias:

But hey, I could be wrong ...

The Electronic Universe Project