The Big Bang is a physical theory that describes how the universe expanded from an initial state of high density and temperature. The notion of an expanding universe was first scientifically originated by physicist Alexander Friedmann in 1922 with the mathematical derivation of the Friedmann equations. The earliest empirical observation of the notion of an expanding universe is known as Hubble's law, published in work by physicist Edwin Hubble in 1929, which discerned that galaxies are moving away from Earth at a rate that accelerates proportionally with distance. Independent of Friedmann's work, and independent of Hubble's observations, physicist Georges Lemaître proposed that the universe emerged from a "primeval atom" in 1931, introducing the modern notion of the Big Bang.
Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate. Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.
The cosmic microwave background, or relic radiation, is microwave radiation that fills all space in the observable universe. With a standard optical telescope, the background space between stars and galaxies is almost completely dark. However, a sufficiently sensitive radio telescope detects a faint background glow that is almost uniform and is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the electromagnetic spectrum. The accidental discovery of the CMB in 1965 by American radio astronomers Arno Penzias and Robert Wilson was the culmination of work initiated in the 1940s.
Observations show that the expansion of the universe is accelerating, such that the velocity at which a distant galaxy recedes from the observer is continuously increasing with time. The accelerated expansion of the universe was discovered in 1998 by two independent projects, the Supernova Cosmology Project and the High-Z Supernova Search Team, which used distant type Ia supernovae to measure the acceleration. The idea was that as type Ia supernovae have almost the same intrinsic brightness, and since objects that are further away appear dimmer, the observed brightness of these supernovae can be used to measure the distance to them. The distance can then be compared to the supernovae's cosmological redshift, which measures how much the universe has expanded since the supernova occurred; the Hubble law established that the further away an object is, the faster it is receding. The unexpected result was that objects in the universe are moving away from one another at an accelerating rate. Cosmologists at the time expected that recession velocity would always be decelerating, due to the gravitational attraction of the matter in the universe. Three members of these two groups have subsequently been awarded Nobel Prizes for their discovery. Confirmatory evidence has been found in baryon acoustic oscillations, and in analyses of the clustering of galaxies.
The Lambda-CDM, Lambda cold dark matter, or ΛCDM model is a mathematical model of the Big Bang theory with three major components:
- a cosmological constant, denoted by lambda (Λ), associated with dark energy
- the postulated cold dark matter, denoted by CDM
- ordinary matter
Katherine Freese is a theoretical astrophysicist. She is currently a professor of physics at the University of Texas at Austin, where she holds the Jeff and Gail Kodosky Endowed Chair in Physics. She is known for her work in theoretical cosmology at the interface of particle physics and astrophysics.
The chronology of the universe describes the history and future of the universe according to Big Bang cosmology.
In physical cosmology and astronomy, dark energy is a proposed form of energy that affects the universe on the largest scales. Its primary effect is to drive the accelerating expansion of the universe. Assuming that the lambda-CDM model of cosmology is correct, dark energy dominates the universe, contributing 68% of the total energy in the present-day observable universe while dark matter and ordinary (baryonic) matter contribute 26% and 5%, respectively, and other components such as neutrinos and photons are nearly negligible. Dark energy's density is very low: 7×10−30 g/cm3, much less than the density of ordinary matter or dark matter within galaxies. However, it dominates the universe's mass–energy content because it is uniform across space.
Alessandra Buonanno is an Italian-American theoretical physicist and director at the Max Planck Institute for Gravitational Physics in Potsdam. She is the head of the "Astrophysical and Cosmological Relativity" department. She holds a research professorship at the University of Maryland, College Park, and honorary professorships at the Humboldt University in Berlin, and the University of Potsdam. She is a leading member of the LIGO Scientific Collaboration, which observed gravitational waves from a binary black-hole merger in 2015.
In cosmology, primordial black holes (PBHs) are hypothetical black holes that formed soon after the Big Bang. In the inflationary era and early radiation-dominated universe, extremely dense pockets of subatomic matter may have been tightly packed to the point of gravitational collapse, creating primordial black holes without the supernova compression typically needed to make black holes today. Because the creation of primordial black holes would pre-date the first stars, they are not limited to the narrow mass range of stellar black holes.
Uroš Seljak is a Slovenian cosmologist and a professor of astronomy and physics at University of California, Berkeley. He is particularly well-known for his research in cosmology and approximate Bayesian statistical methods.
Raphael Bousso is a theoretical physicist and cosmologist. He is a professor at the Berkeley Center for Theoretical Physics in the Department of Physics, UC Berkeley. He is known for the Bousso bound on the information content of the universe. With Joseph Polchinski, Bousso proposed the string theory landscape as a solution to the cosmological constant problem.
John Michael Kovac is an American physicist and astronomer. His cosmology research, conducted at the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts, focuses on observations of the Cosmic Microwave Background (CMB) to reveal signatures of the physics that drove the birth of the universe, the creation of its structure, and its present-day expansion. Currently, Kovac is Professor of Astronomy and Physics at Harvard University.
Licia Verde is an Italian cosmologist and theoretical physicist and currently ICREA Professor of Physics and Astronomy at the University of Barcelona. Her research interests include large-scale structure, dark matter, dark energy, inflation and the cosmic microwave background.
Risa H. Wechsler is an American cosmological physicist, Professor of Physics at Stanford University, and Professor of Particle Physics and Astrophysics at SLAC National Accelerator Laboratory. She is the director of the Kavli Institute for Particle Astrophysics and Cosmology.
Abigail Goodhue Vieregg is a professor of physics at the Enrico Fermi Institute and Kavli Institute of Cosmology, University of Chicago, specializing in neutrino astrophysics and cosmology. Her work focuses on cosmic high-energy neutrinos and mapping the cosmic microwave background.
Katelin Schutz is an American particle physicist known for using cosmological observations to study dark sectors, that is new particles and forces that interact weakly with the visible world. She was a NASA Einstein Fellow and Pappalardo Fellow in the MIT Department of Physics and is currently an assistant professor of physics at McGill University.
George Michael Fuller is an American theoretical physicist, known for his research on nuclear astrophysics involving weak interactions, neutrino flavor-mixing, and quark matter, as well as the hypothetical nuclear matter.
Daniel S. Akerib is an American particle physicist and astrophysicist. He was elected in 2008 a fellow of the American Physical Society (APS).
Raphael Flauger is a German theoretical physicist and cosmologist.
