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| Modified gravity | |
|---|---|
| Name | Modified gravity |
| Field | Physics |
| Known for | Alternatives to General relativity, explanations for cosmic acceleration and dark matter phenomena |
| Notable people | Albert Einstein, Isaac Newton, Jacob Bekenstein, Mordehai Milgrom, Clifford Will, James Jeans, Roger Penrose, Stephen Hawking, Andrei Sakharov, Leonard Susskind, Edward Witten, Juan Maldacena, Kip Thorne, Thibault Damour, Yasunori Nomura, Erik Verlinde, Sabine Hossenfelder, Sean Carroll, Vera Rubin, Sandra Faber, John Moffat, Clifton, Ferreira & Padilla, Patrick Das Gupta, Lee Smolin |
Modified gravity is a broad class of theoretical frameworks that alter or extend the laws of General relativity and Newtonian gravity to account for empirical phenomena attributed to dark matter and dark energy or to resolve conceptual tensions between gravitation and quantum mechanics. Proposals range from phenomenological adjustments to fully covariant field theories and often aim to produce testable predictions for cosmology, astrophysics, and high-energy physics experiments. Debates over modified gravity involve communities across institutions such as CERN, Max Planck Society, Kavli Institute for Theoretical Physics, Perimeter Institute, and journals including Physical Review Letters and Journal of Cosmology and Astroparticle Physics.
Modified gravity emerges from historical developments including Isaac Newton's inverse-square law, the perihelion anomaly of Mercury that motivated Albert Einstein's development of General relativity, and later observational puzzles led by investigators like Vera Rubin and teams at Mount Palomar Observatory. The field encompasses classical alternatives such as Nordström's theory and contemporary proposals that interface with quantum field theory research at institutions like CERN and projects like the Large Hadron Collider. Research programs are pursued by groups at Princeton University, Harvard University, Cambridge University, Stanford University, University of Chicago, University of California, Berkeley, University of Oxford, California Institute of Technology, Massachusetts Institute of Technology, Imperial College London, and national labs such as Los Alamos National Laboratory.
Motivations include unexplained measurements from surveys like the Sloan Digital Sky Survey, the Dark Energy Survey, and the Planck mission that inferred a ΛCDM model requiring cold dark matter and dark energy. Conceptual drives arise from attempts to reconcile gravity with frameworks championed in work by Edward Witten, Juan Maldacena, and Leonard Susskind on string theory and the AdS/CFT correspondence, or alternative quantum gravity programs such as Loop quantum gravity advocated by Carlo Rovelli and Lee Smolin. Additional motivators include singularity resolution studied by Roger Penrose and Stephen Hawking, thermodynamic analogies from Jacob Bekenstein and Ted Jacobson, and entropic perspectives promoted by Erik Verlinde.
Key proposals with extensive literature include Scalar–tensor theories originating from work by Carl Brans and Robert Dicke; f(R) gravity studied in contexts including Starobinsky inflation by Alexei Starobinsky; MOND introduced by Mordehai Milgrom and relativistic completions like TeVeS developed by Jacob Bekenstein; Horndeski theory and its extensions tied to research at Imperial College and by theorists such as Clifton, Ferreira & Padilla; massive gravity frameworks including the de Rham–Gabadadze–Tolley construction; emergent gravity scenarios associated with Erik Verlinde; and higher-dimensional models such as the Randall–Sundrum model and earlier Kaluza–Klein theory connected to work by Theodor Kaluza and Oskar Klein. Quantum-inspired alternatives engage concepts from asymptotic safety studied by Steven Weinberg and causal set theory advocated by Rafael Sorkin.
Modified gravity models predict distinct signatures in structure formation probed by collaborations like Euclid (spacecraft), LSST (now part of Vera C. Rubin Observatory), and the Dark Energy Spectroscopic Instrument. Phenomena analyzed include rotation curves of galaxies originally cataloged by Vera Rubin, dynamics in galaxy clusters observed in studies such as the analysis of the Bullet Cluster by teams using Chandra X-ray Observatory and Hubble Space Telescope, gravitational lensing measured by Sloan Digital Sky Survey teams, cosmic microwave background anisotropies from Planck (spacecraft), and redshift–distance relations from surveys like Supernova Cosmology Project and High-z Supernova Search Team associated with Saul Perlmutter and Adam Riess. Modified gravity can alter predictions for big bang nucleosynthesis constraints studied by George Gamow-inspired programs and for the growth rate of large-scale structure interrogated by BOSS.
Tests span solar-system probes such as Cassini–Huygens timing, light-deflection experiments from expeditions inspired by Arthur Eddington, and lunar laser ranging coordinated by teams at Jet Propulsion Laboratory. Strong-field tests utilize observations of compact objects from LIGO–Virgo Collaboration, black hole imaging by the Event Horizon Telescope collaboration, and pulsar timing arrays including work by NANOGrav. Cosmological tests involve data from Planck (spacecraft), WMAP, Euclid (spacecraft), and ground-based facilities like Atacama Cosmology Telescope and South Pole Telescope. Laboratory experiments and equivalence principle tests are performed at Eöt-Wash group facilities and in space missions such as MICROSCOPE (satellite).
Mathematical approaches employ differential geometry foundational to Riemannian geometry and techniques used by Élie Cartan and Bernhard Riemann, variational principles developed following Leonhard Euler and Lagrange, effective field theory methods applied by Steven Weinberg and John Preskill, and Hamiltonian analyses inspired by Paul Dirac and Richard Arnowitt. Consistency checks require absence of ghosts and instabilities examined in studies by Clifford Will and others, well-posed initial-value formulations investigated in the tradition of Yvonne Choquet-Bruhat, and renormalizability or UV completions explored in work by Gerard 't Hooft and Martinus Veltman.
Open problems include reconciling modified gravity with precision data from collaborations like Planck (spacecraft) and LIGO–Virgo Collaboration, constructing UV-complete theories compatible with results from Large Hadron Collider programs, explaining observations such as the Bullet Cluster in a way competitive with cold dark matter paradigms championed by researchers at Fermi National Accelerator Laboratory, and resolving theoretical issues like stability, causality, and radiative corrections studied in the literature by Thibault Damour and Clifton, Ferreira & Padilla. Future directions involve multi-messenger campaigns coordinated by IceCube Neutrino Observatory and KM3NeT, surveys by Vera C. Rubin Observatory and Euclid (spacecraft), and theoretical synthesis drawing on inputs from string theory programs at Institute for Advanced Study and quantum gravity research at the Perimeter Institute.