However, soon after Einstein developed his static theory, observations by Edwin Hubble indicated that the universe appears to be expanding this was consistent with a cosmological solution to the original general relativity equations that had been found by the mathematician Friedmann, working on the Einstein equations of general relativity. To counteract this possibility, Einstein added the cosmological constant. History Įinstein included the cosmological constant as a term in his field equations for general relativity because he was dissatisfied that otherwise his equations did not allow for a static universe: gravity would cause a universe that was initially non-expanding to contract. This issue is called the cosmological constant problem and it is one of the greatest mysteries in science with many physicists believing that "the vacuum holds the key to a full understanding of nature". The discrepancy between theorized vacuum energy from quantum field theory and observed vacuum energy from cosmology is a source of major contention, with the values predicted exceeding observation by some 120 orders of magnitude, a discrepancy that has been called "the worst theoretical prediction in the history of physics!". These zero-point fluctuations should act as a contribution to the cosmological constant Λ, but when calculations are performed, these fluctuations give rise to an enormous vacuum energy. All these quantum fields exhibit fluctuations in their ground state (lowest energy density) arising from the zero-point energy present everywhere in space. The cosmological constant Λ is the simplest possible explanation for dark energy, and is used in the current standard model of cosmology known as the ΛCDM model.Īccording to quantum field theory (QFT), which underlies modern particle physics, empty space is defined by the vacuum state, which is composed of a collection of quantum fields. Since the 1990s, studies have shown that, assuming the cosmological principle, around 68% of the mass–energy density of the universe can be attributed to so-called dark energy. That changed with the discovery in 1998 that the expansion of the universe is accelerating, implying that the cosmological constant may have a positive value. From the 1930s until the late 1990s, most physicists agreed with Einstein's choice of setting the cosmological constant to zero. Einstein's cosmological constant was abandoned after Edwin Hubble's confirmation that the universe was expanding. Įinstein originally introduced the constant in 1917 to counterbalance the effect of gravity and achieve a static universe, a notion that was the accepted view at the time. ![]() It is closely associated with the concept of dark energy. Much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. Is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ), alternatively called Einstein's cosmological constant,
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