Ideally, it is the volume of space that consists intrinsic basic energy. It is equivalent to vacuum energy in reality since it is the energy density of unfilled vacuum. The general relativity theory denotes that the energy will have an effect on gravity (Wang 76). Cosmological constant is characterized by negative pressure that is equivalent to its energy density. As such, it causes acceleration on the expansion of the universe.
Quintessence refers to the hypothetical form of energy that can be attractive or repulsive. It is a scalar field that has its equation defined by the ratio of pressure to its density. Attraction or repulsion of this energy is dependent on the kinetic to potential energy ratio (Morrey Bsc & Morrey 112). Quintessence serves to solve part of the problems accruing from cosmological constant. Unlike cosmological constant, quintessence is a dynamic equation that varies with time. In addition, it differs from cosmological constant from the fact that it forecasts a slower increase in rate of expansion of the universe.
The third alternative idea stems from the string theory. String theory stipulates that an atom’s elementary particles are dimensional swinging lines (Amendola and Tsujikawa 64). It is a quantum theory of gravity. The theory comprises configurations that define all observed basic forces and matter, but have zero cosmological constant.
The methods employed in determine the above ideas are geometry of space, exploding stars and the late- time integrated Sachs- Wolfe effect (Amendola andTsujikawa 340). Exploding stars is ideally the supernovae. Type la supernovae offer a standard candle for the measurement of the distance to galaxies that are much far away. It combines the information with redshift; a measure for the speed at which galaxy recedes. Conclusively, astronomers have inference that there is a factor that is contributing to the increased velocity of the recession of galaxies.