cosmological constant

cosmological constant
Name	Cosmological constant
Field	General relativity, Cosmology
Introduced	1917
Introduced by	Albert Einstein
Units	m−2

Contents

cosmological constant

Introduction

The cosmological constant is a parameter in General relativity introduced by Albert Einstein in 1917 to allow static Universe solutions; it now appears as a candidate description of Dark energy driving the accelerating expansion discovered in observations by teams including the Supernova Cosmology Project and the High-Z Supernova Search Team. Historically tied to the development of Friedmann equations and the Friedmann–Lemaître–Robertson–Walker metric, the constant is central to the standard Lambda-CDM model used in analyses by collaborations such as Planck (spacecraft), the Sloan Digital Sky Survey, and the Dark Energy Survey. The term influences interpretations across theoretical frameworks associated with Quantum field theory, String theory, and proposals from researchers at institutions like Princeton University and Institute for Advanced Study.

Einstein introduced the term to modify the Einstein field equations after the work of Willem de Sitter and contemporaneous results from Alexander Friedmann suggested non-static solutions; other figures such as Georges Lemaître later reinterpreted related models that incorporated expanding solutions consistent with observations by Vesto Slipher and Edwin Hubble. Debates featured commentators including Arthur Eddington, George Gamow, and Howard Robertson as cosmology matured through the 1920s–1950s and into the Big Bang theory era; the term regained prominence after late 20th-century measurements by teams led by Saul Perlmutter, Adam Riess, and Brian Schmidt. Theoretical puzzles, framed by work of Steven Weinberg, Yakov Zel'dovich, and Sidney Coleman, focused attention on a severe discrepancy between observed values and vacuum energy estimates from quantum field theory and estimates by groups in CERN and SLAC National Accelerator Laboratory.

In the formalism of Albert Einstein the constant enters the Einstein field equations as an additional term proportional to the metric tensor, modifying curvature–matter relations that had been elaborated in mathematical treatments by Tullio Levi-Civita and Marcel Grossmann. Solutions such as the de Sitter space and Anti-de Sitter space are characterized by positive or negative values of the constant and are central to theoretical constructions including the AdS/CFT correspondence explored by researchers at Harvard University and Institute for Advanced Study. The term contributes an effective stress–energy tensor with equation-of-state parameter w = −1 often used in observational fits by collaborations like WMAP (spacecraft) and Planck (spacecraft), and it interacts conceptually with mechanisms studied in Inflation (cosmology) scenarios originally proposed by Alan Guth and refined by Andrei Linde.

Accelerated expansion inferred from Type Ia supernova observations by groups including the Supernova Cosmology Project and the High-Z Supernova Search Team led to revival of the constant as an explanation of Dark energy consistent with measurements from Cosmic microwave background experiments such as WMAP (spacecraft) and Planck (spacecraft), and with large-scale structure surveys like the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey. Independent constraints arise from baryon acoustic oscillation measurements by teams using instruments at facilities such as the Anglo-Australian Observatory and the Baryon Oscillation Spectroscopic Survey, and from weak lensing surveys run by groups including the Dark Energy Survey. The inferred small positive value has profound implications for the ultimate fate scenarios discussed by theorists at Cambridge University, University of Chicago, and University of California, Berkeley, affecting considerations related to Heat death of the universe and proposals by researchers such as Roger Penrose and Stephen Hawking.

Interpretations span straightforward identification with vacuum energy from Quantum field theory and renormalization schemes developed in contexts including Quantum electrodynamics at institutions like Massachusetts Institute of Technology and CERN, to dynamical dark energy models such as Quintessence proposed by researchers at Princeton University and University of Pennsylvania. Alternatives include modified-gravity approaches like f(R) gravity explored by groups at Kavli Institute for Cosmological Physics and MOND-inspired frameworks initiated by Mordehai Milgrom, while ideas from String theory and the Landscape (string theory) invoke anthropic reasoning discussed by proponents such as Leonard Susskind and critics including Paul Steinhardt. Efforts to reconcile the cosmological constant with particle physics have engaged figures like Nima Arkani-Hamed, Edward Witten, and Gian Francesco Giudice, and experimental programs at Large Hadron Collider search for indirect signatures related to vacuum structure.

In the concordance Lambda-CDM model the constant provides the simplest parametrization of Dark energy and combines with Cold dark matter to fit diverse datasets compiled by projects such as Planck (spacecraft), Sloan Digital Sky Survey, Dark Energy Survey, and ground-based observatories including Keck Observatory and Very Large Telescope. The model informs parameter estimation pipelines developed by collaborations like Cosmology Large Angular Scale Surveyor and theoretical interpretation groups at Stanford University and Caltech, while tensions such as the Hubble tension motivate exploration of extensions including early dark energy scenarios by teams at University of Cambridge and University of Oxford. The cosmological constant thus remains a focal point linking observational campaigns, theoretical research at institutions like Perimeter Institute and Institute for Advanced Study, and philosophical questions addressed by scholars at Princeton University and University of Chicago.

Category:Physical constants