Dark Energy
  Dark energy is one of the mysteries of modern science. It is unlike any known
form of matter or energy and has been detected so far only by its gravitational
effect of repulsion. Owing to its effects being discernible only at very very
large distance scales, dark energy was only detected at the turn of the last
century when technology had advanced enough to observe a greater part of the
universe in finer detail. The aim of the report is to gain a better
understanding of the mysterious dark energy. To this end, both theoretical
methods and observational evidence are studied. Three lines of evidence,
namely, the redshift data of type Ia supernovae, estimates of the age of the
universe by various methods, and the anisotropies in the cosmic background
radiation, build the case for existence of dark energy. The supernova data
indicate that the expansion of the universe is accelerating. The ages of the
oldest star clusters in the universe indicate that the universe is older than
previously thought to be. The anisotropies in the cosmic microwave background
radiation suggest that the universe is globally spatially flat. If one agrees
that the dynamics of the geometry of the universe is dictated by its
energy-momentum content through Einstein's general theory of relativity, then
all these independent observations lead to the amazing conclusion that the
amount of energy in the universe that is presently accounted for by matter and
radiation is not enough to explain these phenomena. One of the best and
simplest explanations for dark energy is the cosmological constant. While it
does not answer all questions, it certainly does manage to explain the
observations. The following report examines in some detail the dark energy
problem and the candidacy of the cosmological constant as the right theory of
dark energy.
