Final Cosmological Remarks
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
- Evidence for Dark Matter is abundant on galactic and cluster
- Most data indicate that OMEGA is in the range 0.1--0.3 -->
there is rather little evidence for OMEGA = 1 but this may be a
reflection of not obtaining the right sample to do the experiment
correctly (see Strauss and Willick 1995).
- If OMEGA = 1 then it is clear that the great
majority of the DM must be non-baryonic. The existence of non-baryonic
gravitating DM may be key to the formation of galaxies in the Universe
as such material will be much less affected by radiation drag in the
early Universe and hence density perturbations can begin to grow at
very early times.
How did structure form in the Universe and what formation
scenarios are consistent with the current observational data?
A quick summary is trivial: we
don't have a structure formation scenario that works. More definitively,
no single structure formation scenario can satisfy the simultaneous
large and small scale constraints.
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?
- Traditional CDM model over-produces small scale structure when normalized to the COBE
- Hence to retain this model once must think of ways that small scale
structure has been surpressed. Lmabda dominated models can do this
as they allow for along time for radiation and matter density to
equilibrate thus increasing the probability that small scale fluctuations
will be erased.
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.
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:
- H is 85--90
- Neutrinos have mass in the range 1--3 eV
- Lambda is 0.8--0.9
- Inflation is correct
- The CDM seed particle will remain mysterious for
the next few decades. SUSY will be ruled out when the Higgs
field is discovered at energies in excess of 135 Gev.
- We will never understand galaxy formation
But hey, I could be wrong ...
The Electronic Universe Project