How far can we push the SN measurements? Finding more and more SNe allows us to beat down statistical errors to arbitrarily small levels but, ultimately, systematic effects will limit the precision to which SNIa magnitudes can be applied to measure distances. Our best estimate is that it will be possible to control systematic effects from ground-based experiments to a level of ~ 0.03 mag. Carefully controlled ground-based experiments on 200 SNe will reach this statistical uncertainty in z = 0.1 redshift bins in the range z = 0.3 - 0.7, and is achievable within five years. A comparable quality low redshift sample, with 300 SNe in z = 0.02 - 0.08, will also be achievable in that time frame [2].
The SuperNova/Acceleration Probe (SNAP) collaboration (1) has proposed to launch a dedicated cosmology satellite [1, 68] - the ultimate SNIa experiment. This satellite will, if funded, scan many square degrees of sky, discovering well over a thousand SNIa per year and obtain their spectra and light curves out to z = 1.7. Besides the large numbers of objects and their extended redshift range, space-based observations will also provide the opportunity to control many systematic effects better than from the ground [21, 53]. Fig. 7 shows the expected precision in the SNAP and ground-based experiments for measuring w, assuming a flat Universe. Perhaps the most important advance will be the first studies of the time variation of the equation of state w (see the right panel of Fig. 7 and [40, 103]).
![]() |
Figure 7. Future expected constraints on
dark energy: Left panel:
Estimated 68% confidence regions for a
constant equation of state parameter for
the dark energy, w, versus mass density, for a ground-based
study with 200 SNe between z = 0.3 - 0.7 (open contours), and
for the satellite-based SNAP experiment with 2,000 SNe between
z = 0.3 - 1.7
(filled contours). Both experiments are assumed to also use 300
SNe between z = 0.02 - 0.08.
A flat cosmology is assumed (based on Cosmic
Microwave Background (CMB)
constraints) and the inner (solid line) contours for each experiment
include tight constraints (from large scale structure surveys)
on |
With rapidly improving CMB data from interferometers, the satellites
Microwave Anisotropy Probe (MAP) and
Planck, and balloon-based instrumentation planned for the next
several years,
CMB measurements promise dramatic improvements in precision on
many of the
cosmological parameters. However, the CMB measurements are
relatively insensitive to the dark energy and the epoch of cosmic
acceleration.
SNIa are currently the only way to directly study this acceleration
epoch with sufficient
precision (and control on systematic uncertainties) that we can
investigate the
properties of the dark energy, and any time dependence in these properties.
This ambitious goal will require complementary and supporting measurements
of, for example,
M from
CMB, weak lensing, and large scale structure.
The SN measurements will also provide a test of the cosmological results
independent from these other techniques, which have their own systematic
errors. Moving forward
simultaneously on these experimental fronts offers the plausible and
exciting possibility of achieving a comprehensive measurement of the
fundamental properties of our Universe.
1 See http://snap.lbl.gov Back.