Dark energy

Dark energy
NASA / WMAP Science Team · Public domain · source
Name	Dark energy
Field	Cosmology, Astrophysics
Discovered	1998
Discoverers	Supernova Cosmology Project, High-Z Supernova Search Team

Dark energy Dark energy is the hypothesized component driving the accelerated expansion of the observable universe, inferred from multiple astrophysical observations and cosmological probes. The concept emerged from late-20th-century measurements and has since become central to the Lambda Cold Dark Matter model, influencing interpretations of data from observatories and missions.

Introduction

The discovery that the expansion rate of the universe is accelerating was announced by teams including the Supernova Cosmology Project and the High-Z Supernova Search Team, following surveys using the Hubble Space Telescope and ground-based facilities such as the Keck Observatory and the Cerro Tololo Inter-American Observatory. Subsequent confirmation came via independent programs including the Sloan Digital Sky Survey, the Two-degree Field Galaxy Redshift Survey, and measurements from the Wilkinson Microwave Anisotropy Probe and the Planck mission. The acceleration is commonly incorporated into the Lambda Cold Dark Matter model as a cosmological constant term attributed to dark energy, linking developments from Albert Einstein's introduction of the cosmological constant through modern parameter estimation by collaborations such as the Dark Energy Survey. Major institutions active in dark energy research include the European Southern Observatory, the National Aeronautics and Space Administration, and the European Space Agency.

Observational Evidence

Type Ia supernova observations from teams like the Supernova Cosmology Project and the High-Z Supernova Search Team provided the initial empirical basis, supported by distance-redshift relations measured with instruments including the Hubble Space Telescope and the Subaru Telescope. Independent lines of evidence arise from measurements of anisotropies in the cosmic microwave background by the Wilkinson Microwave Anisotropy Probe and Planck, baryon acoustic oscillation detections by surveys such as the Sloan Digital Sky Survey and the Baryon Oscillation Spectroscopic Survey, and large-scale structure mapping from the Two-degree Field Galaxy Redshift Survey and the Dark Energy Survey. Observations of galaxy clusters by the Chandra X-ray Observatory and the XMM-Newton mission, gravitational lensing analyses by teams using the Subaru Telescope and the Hubble Space Telescope, and constraints from nucleosynthesis studies tied to the Big Bang framework further corroborate a component consistent with dark energy.

Theoretical Models

The simplest theoretical representation is the cosmological constant Λ, originally proposed by Albert Einstein and now treated as vacuum energy density in the Lambda Cold Dark Matter model, with quantum vacuum interpretations connecting to calculations by researchers influenced by work from Paul Dirac and others. Dynamical scalar-field models such as quintessence draw on frameworks related to theories developed by Robert R. Caldwell and collaborators, while modifications of general relativity have been explored in contexts associated with work by Clifton, Ferreira, Padilla, and Skordis and others investigating f(R) gravity and braneworld scenarios inspired by Lisa Randall and Sundrum. Alternative proposals include interacting dark sector models examined by groups associated with the Perimeter Institute and emergent gravity ideas influenced by perspectives from Erik Verlinde and extensions connected to string-theory motivated landscapes discussed by researchers at institutions like the Institute for Advanced Study and CERN.

Properties and Effects on Cosmology

Dark energy influences the Friedmann equations central to Alexander Friedmann's solutions and alters the universe's expansion history probed by projects including the Dark Energy Survey and the Large Synoptic Survey Telescope (now Vera C. Rubin Observatory). Its equation of state parameter w, constrained in studies referencing methods developed by Michael S. Turner and others, determines whether the expansion approaches de Sitter evolution associated with concepts from Willem de Sitter or leads to phantom scenarios discussed in theoretical work by Rainer Essig and colleagues. The presence of dark energy affects the growth rate of cosmic structure analyzed in studies by the 2dFGRS team and the Sloan Digital Sky Survey collaboration, modifies predictions for the fate of bound systems as considered in thought experiments by Frank J. Tipler-type discussions, and impacts cosmic age estimates refined by groups using data from the Hubble Space Telescope and stellar-population analyses at observatories such as the European Southern Observatory.

Constraints and Measurements

Parameters describing dark energy are constrained by combinations of data from the Planck team, supernova compilations from the Supernova Cosmology Project and the High-Z Supernova Search Team, baryon acoustic oscillation results from the Baryon Oscillation Spectroscopic Survey and WiggleZ surveys, and weak lensing measurements by the Dark Energy Survey and the Kilo-Degree Survey. Joint analyses by consortia including the Joint Light-curve Analysis group and collaborations supported by agencies like the National Science Foundation and European Research Council deliver bounds on the equation of state parameter w and constraints on spatial curvature first formalized in work linked to Georges Lemaître. Laboratory and astrophysical null tests of deviations from general relativity draw on studies by groups at the Max Planck Institute for Astrophysics and teams affiliated with the Perimeter Institute.

Open Questions and Future Research

Key unresolved issues include the physical origin of the cosmological-constant scale highlighted in debates following contributions by Steven Weinberg and the coincidence problem emphasized in reviews by P. J. E. Peebles and Bjørn R. M. S. Hansen-linked literature. Upcoming and planned programs such as the Euclid mission, the Nancy Grace Roman Space Telescope, the Vera C. Rubin Observatory, and extensions of the Dark Energy Survey aim to tighten constraints through coordinated surveys and cross-correlation analyses developed by teams at institutions like the Lawrence Berkeley National Laboratory and the Jet Propulsion Laboratory. Theoretical work continues at centers including Princeton University, the Institute for Advanced Study, and CERN to reconcile vacuum-energy estimates from quantum field theory with cosmological measurements, explore novel observational signatures predicted by modified-gravity frameworks, and design targeted probes for distinguishing among competing models.

Category:Cosmology