4. CHECKLIST FOR THE NEXT DECADE
As I have been careful to stress the basic tenets of Inflation
+ Cold Dark Matter have not yet been confirmed definitively.
However, a flood of high-quality cosmological data is
coming, and could make the case in the next decade.
Here is my version of how "maybe" becomes "yes."
- Map of the Universe at 300,000 yrs. COBE mapped
the CMB with an angular resolution of around 10°;
two new satellite missions, NASA's MAP (launch 2000)
and ESA's Planck Surveyor (launch 2007), will map the
CMB with 100 times better resolution (0.1°). From
these maps of the Universe as it existed at a
simpler time, long before the first stars and
galaxies, will come a gold mine of information:
Among other things, a definitive measurement of
a determination of the Hubble constant to a precision of
better than 5%;
a characterization of the primeval lumpiness; and possible
detection of the relic gravity waves from inflation.
The precision maps of the CMB that will be made are crucial
to establishing Inflation + Cold Dark Matter.
- Map of the Universe today. Our knowledge of the structure
of the Universe is based upon maps constructed from the positions
of some 30,000 galaxies in our own backyard. The Sloan Digital
Sky Survey will
produce a map of a representative portion of the Universe,
based upon the positions of a million galaxies.
The Anglo-Australian 2-degree Field survey will determine the position of
several hundred thousand galaxies. These surveys will
define precisely the large-scale structure that exists today,
answering questions such as, "What are the largest structures
that exist?" Used together with
the CMB maps, this will definitively test the Cold
Dark Matter theory of structure formation, and much more.
- Present expansion rate H0. Direct measurements
of the expansion rate using standard candles, gravitational time
delay, SZ imaging and the CMB maps will pin down the elusive
Hubble constant once and for all. It is the fundamental parameter
that sets the size - in time and space - of the observable Universe.
Its value is critical to testing the self consistency of Cold
- Cold dark matter. A key element of theory is the
cold dark matter particles that hold the Universe together;
until we actually
detect cold dark matter particles, it will be difficult to argue
that cosmology is solved.
Experiments designed to detect the dark matter that
holds are own galaxy together are now operating with sufficient
sensitivity to detect both neutralinos and axions.
In addition, experiments at particle accelerators (Fermilab
and CERN) will be hunting for the neutralino and its other
- Nature of the dark energy. If the Universe is indeed accelerating,
then most of the critical density exists in the form of dark energy. This
component is poorly understood. Vacuum energy is only the
simplest possibly for the smooth dark component; there are
other possibilities: frustrated topological defects
or an evolving scalar field (see e.g.,
Caldwell et al, 1998;
Turner & White, 1997).
Independent evidence for the existence
of this dark energy, e.g., by CMB anisotropy, the SDSS and 2dF
surveys, or gravitational
lensing, is crucial for verifying the accounting of matter and energy
in the Universe I have advocated. Additional measurements of SNe1a could
help shed light on the precise nature of the dark energy. The dark
energy problem is not only of great importance for cosmology, but
for fundamental physics as well. Whether it is vacuum energy or
quintessence, it is a puzzle for fundamental physics and possibly
a clue about the unification of the forces and particles.