Dark energy, also called quintessence, is a mysterious energy or force that has been postulated by astronomers and cosmologists to explain recent observations suggesting that the universe is expanding at an ever-increasing rate of speed. Dark energy affects the behavior of photon s (light particles) as they travel through space.
An exact definition of dark energy has eluded scientists. One description is that it is like gravity , but is repulsive (outward-pushing) rather than attractive (inward-pulling), and operates over a much larger scale than conventional gravity. The existence of dark energy is inferred from the apparent acceleration in the universe's expansion, and also from observed irregularities in the cosmic background radiation that many attribute to effects from a hypothesized Big Bang. The term Big Bang refers to the theory that a gigantic explosion took place approximately 12 billion (1.2 x 10 10 ) years ago, in which all the matter and energy in the known universe emanated from a single point or tiny primordial particle.