# Article

# Article

- Astronomy & Space Science
- Cosmology
- Cosmological constant

# Cosmological constant

Article By:

**Caldwell, Robert **Department of Physics and Astronomy, Dartmouth College, Hanover, New Hampshire.

Last reviewed:2014

DOI:https://doi.org/10.1036/1097-8542.800540

- Introduction by Einstein
- De Sitter model
- Quantum vacuum as a source
- Arguments for zero value

- Relation to cosmic acceleration
- Energy scales
- Consequences of nonzero value

- Prospects
- Links to Primary Literature
- Additional Readings

**The constant gravitational source added to the general theory of relativity by Albert Einstein to balance the gravitational field equations necessary for a static universe.** In formulas it is denoted Λ (lambda) and has units of curvature, or (length)^{−2}. The existence of the cosmological constant would mean that empty space gravitates as if it were filled by a static, uniform energy density ρ = Λ*c*^{4}/8π*G* and pressure *p* = −ρ, where *G* is Newton's constant of gravitation and *c* is the speed of light. It is speculated to be responsible for dark energy, because a sufficiently large cosmological constant would cause the accelerated expansion of spacetime. However, the physical origin of the cosmological constant is not understood. Quantum theory predicts the existence of the cosmological constant, but with an energy density that is approximately 10^{120} times too large to be compatible with observations. This gross mismatch between theory and observation, known as the cosmological-constant problem, is a deep enigma. It is thought that a resolution requires a quantum theory of gravity. Testing for the existence of the cosmological constant is a major goal of current physics and astronomy research. * See also: ***Accelerating universe**; **Dark energy**; **Quantum gravitation**; **Relativity**

The content above is only an excerpt.

for your institution. Subscribe

To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.

to your librarian. Recommend

Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.

## About AccessScience

#### AccessScience provides the most accurate and trustworthy scientific information available.

Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.

**MORE THAN 8500** articles and Research Reviews covering all major scientific disciplines and encompassing the *McGraw-Hill Encyclopedia of Science & Technology* and *McGraw-Hill Yearbook of Science & Technology *

**115,000-PLUS** definitions from the *McGraw-Hill Dictionary of Scientific and Technical Terms *

**3000** biographies of notable scientific figures

**MORE THAN 19,000** downloadable images and animations illustrating key topics

**ENGAGING VIDEOS** highlighting the life and work of award-winning scientists

**SUGGESTIONS FOR FURTHER STUDY** and additional readings to guide students to deeper understanding and research

**LINKS TO CITABLE LITERATURE** help students expand their knowledge using primary sources of information