Fidele J. Twagirayezu
The relation between Albert Einstein's Cosmological Constant and Dark Energy
The idea of the expending universe, which is now known to be accelerating, began with Albert Einstein in his theory of general relativity when he tried to apply his new theory of gravity to the universe as a whole, he automatically realized that the theory predicts collapsing or expanding universe, But he did not like it he felt comfortable with unchanging and static universe, then he added the cosmological constant in his equations to balance the effect of gravity.
Few scientists have been looking for other solutions to Einstein's equations, for example a Belgian astrophysicist Georges Lemaitre took Einstein 's equations and analyzed them carefully he finally found that they were predicting the expending universe, and he thought that if the universe is expanding ,that is means, it was small and dense in the past, form this idea he found the theory of the big bang .In these solutions, the light coming from distant objects would be red shifted as it traveled through the expanding universe. The red shift would increase with increasing distance to the object.
The work of Edwin Hubble at the Carnegie Observatories in Pasadena, California, by measuring the red shifts of a number of distant galaxies, confirmed that the solutions of Einstein's Equations predicting the expanding universe are absolutely right. Once scientists understood that the universe was expanding they tried to know the cause of its expansion. Based on modern theories and observations of evolution of the universe, they realized that the cause of expansion of the universe is a mysterious energy called Dark energy that is now accelerating our universe.
In Modern physics, quantum theory requires empty space to be filled with particles and anti-particles being continually created and annihilated. This could involve a net vacuum energy which, if present, would behave like a repulsive force at large enough distances .If this view is correct, then the source of the acceleration of the universe is the vacuum that surrounds and permeates each one of us This mysterious vacuum energy of empty space is considered by scientists as Dark energy .
Theories relating the dark energy are also based on the equation describing the evolution of the universe. Such evolutions are also closely related to the theory of relativity advanced by Albert Einstein. In modern terms the cosmological constant is viewed as a quantum mechanical phenomenon called the energy of the vacuum. The new data shows that none of the fancy new theories that have been proposed in the last decade are necessary to explain the acceleration. Rather, vacuum energy is the most likely cause and the expansion history of the universe can be explained by simply adding this constant background of acceleration into the normal theory of gravity.
- "Cosmological Constant or Dark Energy".Universe101.Our Universe.NASA. http://map.gsfc.nasa.gov/universe/uni_accel.html
- Sean M. Carroll. "The Cosmological Constant". University of Chicago .Department of Physics. http://ned.ipac.caltech.edu/level5/Carroll2/frames.html