Sahni, Varun2012-03-132012-03-132002-04-01http://hdl.handle.net/11007/1394Observations of high redshift type Ia supernovae indicate that the universe is accelerating, fueled by an unknown form of dark energy having large negative pressure p < 0. The simplest example of dark energy is the cosmological constant (p ¼ q K=8pGÞ. The cosmological constant arises at a fundamental level from one-loop quantum effects which generate a K-term many orders of magnitude larger than the observed value of dark energy 10 47 GeV4 . This leads to the cosmological constant problem . Dynamical models of dark energy include scalar fields with exponential and power law potentials. Dark energy can also be generated in extra-dimensional braneworld models. Model-inde- pendent methods which attempt to reconstruct dark energy from supernova observations are discussed. 2002 Elsevier Science Ltd. All rights reservedenDark energyObservational case for dark energyArticle