Constant representing stress–energy density of the vacuum
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In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ), alternatively called Einstein's cosmological constant,
is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. He later removed it, however much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy.[1]
Einstein originally introduced the constant in 1917[2] to counterbalance the effect of gravity and achieve a static universe, a notion that was the accepted view at the time. Einstein's cosmological constant was abandoned after Edwin Hubble's confirmation that the universe was expanding.[3] From the 1930s until the late 1990s, most physicists agreed with Einstein's choice of setting the cosmological constant to zero.[4] 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.[5]
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.[6][7][8] 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.
According 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. All these quantum fields exhibit fluctuations in their ground state (lowest energy density) arising from the zero-point energy present everywhere in space. 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.[9] 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!".[10] 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".[11]
^Cite error: The named reference CC Definition was invoked but never defined (see the help page).
^Einstein (1917)
^Cite error: The named reference Rugh 2001 3 was invoked but never defined (see the help page).
^Cite error: The named reference Λ = 0? was invoked but never defined (see the help page).
^Cite error: The named reference 1998 Discovery was invoked but never defined (see the help page).
^Ellis, G. F. R. (2009). "Dark energy and inhomogeneity". Journal of Physics: Conference Series. 189 (1): 012011. Bibcode:2009JPhCS.189a2011E. doi:10.1088/1742-6596/189/1/012011. S2CID 250670331.
^Jacques Colin; Roya Mohayaee; Mohamed Rameez; Subir Sarkar (20 November 2019). "Evidence for anisotropy of cosmic acceleration". Astronomy and Astrophysics. 631: L13. arXiv:1808.04597. Bibcode:2019A&A...631L..13C. doi:10.1051/0004-6361/201936373. S2CID 208175643. Retrieved 25 March 2022.
^Redd (2013)
^Rugh & Zinkernagel (2001), p. 1
^Cite error: The named reference CC Problem was invoked but never defined (see the help page).
^Cite error: The named reference CC Problem 3 was invoked but never defined (see the help page).
and 22 Related for: Cosmological constant information
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a steady-state universe, Einstein added what was later called a cosmologicalconstant to his equations. Einstein's model of a static universe was proved...
{\displaystyle \Lambda } is the cosmologicalconstant and κ {\displaystyle \kappa } is the Einstein gravitational constant. The Einstein tensor is defined...
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value}}{\text{theoretical value}}}} Examples include Einstein's cosmologicalconstant, dark energy, the initial proposals of dark matter and inflation...
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gravitational repulsion in the cosmological context, which accelerates the expansion of the universe. A cosmologicalconstant also has this effect. Mathematically...
physical cosmology, current observations in favor of an accelerating universe imply the existence of a tiny, but nonzero cosmologicalconstant. This problem...
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The cosmologicalconstant, which can be thought of as the density of dark energy in the universe, is a fundamental constant in physical cosmology that...
Subsequent modelling of the universe explored the possibility that the cosmologicalconstant, introduced by Einstein in his 1917 paper, may result in an expanding...
the Einstein tensor (not the gravitational constant despite the use of G), Λ is the cosmologicalconstant, gμν is the metric tensor, Tμν is the stress–energy...
isotropic, that is, the cosmological principle; empirically, this is justified on scales larger than the order of 100 Mpc. The cosmological principle implies...
contributed by a cosmologicalconstant. Steven Weinberg gave an anthropic explanation for this fact: he noted that the cosmologicalconstant has a remarkably...
observed is the backward light cone, which delimits the cosmological horizon. The cosmological horizon, also called the particle horizon or the light horizon...
supernova observations by the Supernova Cosmology Project and High-Z Supernova Search Team. How to add a cosmologicalconstant or quintessence to a theory is discussed...
the cosmological principle. The universality of physical laws is one of the underlying principles of the theory of relativity. The cosmological principle...
the end of cosmology as we know it as the distant universe turns dark. A constantly expanding universe with a non-zero cosmologicalconstant has mass density...
universe is hyperbolic or flat, or if dark energy is a positive cosmologicalconstant, the universe will continue expanding forever, and a heat death...
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