### 9. THE NEXT HUNDRED YEARS

The progress in cosmology over the last hundred years has
been stunning. With the hot big-bang cosmology we
can trace the history of the Universe to within
a fraction of a second of the beginning.
Beyond the standard cosmology, we have promising ideas,
rooted in fundamental theory,
about how to extend our understanding to even earlier
times addressing more profound questions, e.g., inflation
+ cold dark matter. While it remains to be seen whether
or not the expansion is accelerating,
it is a fact that our knowledge of the Universe is accelerating,
driven by new observational results.
Cosmology seems to be in the midst of a golden age;
within ten years we may have a cosmological theory that explains
almost all the fundamental features of the Universe,
the smoothness and flatness, the heat of the CMB, the
baryon asymmetry, and the origin of structure.

There are still larger questions to be answered and to be
asked. What is the global topology of the Universe?
Did the Universe begin with more than four dimensions?
Is inflation the dynamite of the big bang, and were there
other such big bangs? Are there cosmological signatures of the
quantum gravity epoch?

It is difficult - and dangerous - to speculate where
cosmology will go in the next twenty years, let alone
the next hundred. One can never predict the
serendipitous discovery that radically transforms our understanding.
In an age of expensive, complex, and highly focused experiments,
we must be especially vigilant and keep an open mind. And it
can be argued that the two most important discoveries in cosmology
- the expansion and the CMB - were unexpected.
In astrophysics, it is usually a safe bet that things are
more complicated than expected. But then again, Einstein's
ansatz of large-scale homogeneity and isotropy - made to make
the equations of general relativity tractable - turned out to
be a remarkably good description of the Universe.