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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.
Edwin Powell Hubble was an American astronomer. He played a crucial role in establishing the fields of extragalactic astronomy and observational cosmology.
In physics, a redshift is an increase in the wavelength, and corresponding decrease in the frequency and photon energy, of electromagnetic radiation. The opposite change, a decrease in wavelength and increase in frequency and energy, is known as a blueshift, or negative redshift. The terms derive from the colours red and blue which form the extremes of the visible light spectrum. The main causes of electromagnetic redshift in astronomy and cosmology are the relative motions of radiation sources, which give rise to the relativistic Doppler effect, and gravitational potentials, which gravitationally redshift escaping radiation. All sufficiently distant light sources show cosmological redshift corresponding to recession speeds proportional to their distances from Earth, a fact known as Hubble's law that implies the universe is expanding.
In cosmology, the cosmological constant, alternatively called Einstein's cosmological constant, is the constant coefficient of a term that Albert Einstein temporarily added to his field equations of general relativity. He later removed it, however much later it was revived and reinterpreted as the energy density of space, or vacuum energy, that arises in quantum mechanics. It is closely associated with the concept of dark energy.
A gravitational lens is matter, such as a cluster of galaxies or a point particle, that bends light from a distant source as it travels toward an observer. The amount of gravitational lensing is described by Albert Einstein's general theory of relativity with much greater accuracy than Newtonian physics, which treats light as corpuscles travelling at the speed of light.
The following is a timeline of gravitational physics and general relativity.
This timeline of cosmological theories and discoveries is a chronological record of the development of humanity's understanding of the cosmos over the last two-plus millennia. Modern cosmological ideas follow the development of the scientific discipline of physical cosmology.
Kip Stephen Thorne is an American theoretical physicist known for his contributions in gravitational physics and astrophysics. Along with Rainer Weiss and Barry C. Barish, he was awarded the 2017 Nobel Prize in Physics for his contributions to the LIGO detector and the observation of gravitational waves.
An Einstein ring, also known as an Einstein–Chwolson ring or Chwolson ring, is created when light from a galaxy or star passes by a massive object en route to the Earth. Due to gravitational lensing, the light is diverted, making it seem to come from different places. If source, lens, and observer are all in perfect alignment (syzygy), the light appears as a ring.
Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors.
Tired light is a class of hypothetical redshift mechanisms that was proposed as an alternative explanation for the redshift-distance relationship. These models have been proposed as alternatives to the models that involve the expansion of the universe. The concept was first proposed in 1929 by Fritz Zwicky, who suggested that if photons lost energy over time through collisions with other particles in a regular way, the more distant objects would appear redder than more nearby ones.
Cosmology is a branch of physics and metaphysics dealing with the nature of the universe, the cosmos. The term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, and in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis. Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation myths and eschatology. In the science of astronomy, cosmology is concerned with the study of the chronology of the universe.
James Edward Gunn is the Eugene Higgins Professor of Astronomy at Princeton University. Gunn's early theoretical work in astronomy has helped establish the current understanding of how galaxies form, and the properties of the space between galaxies. He also suggested important observational tests to confirm the presence of dark matter in galaxies, and predicted the existence of a Gunn–Peterson trough in the spectra of distant quasars.
The expansion of the universe is the increase in distance between gravitationally unbound parts of the observable universe with time. It is an intrinsic expansion; the universe does not expand "into" anything and does not require space to exist "outside" it. To any observer in the universe, it appears that all but the nearest galaxies recede at speeds that are proportional to their distance from the observer, on average. While objects cannot move faster than light, this limitation only applies with respect to local reference frames and does not limit the recession rates of cosmologically distant objects.
Charles W. Misner was an American physicist and one of the authors of Gravitation. His specialties included general relativity and cosmology. His work has also provided early foundations for studies of quantum gravity and numerical relativity.
An inhomogeneous cosmology is a physical cosmological theory which, unlike the currently widely accepted cosmological concordance model, assumes that inhomogeneities in the distribution of matter across the universe affect local gravitational forces enough to skew our view of the Universe. When the universe began, matter was distributed homogeneously, but over billions of years, galaxies, clusters of galaxies, and superclusters have coalesced, and must, according to Einstein's theory of general relativity, warp the space-time around them. While the concordance model acknowledges this fact, it assumes that such inhomogeneities are not sufficient to affect large-scale averages of gravity in our observations. When two separate studies claimed in 1998-1999 that high redshift supernovae were further away than our calculations showed they should be, it was suggested that the expansion of the universe is accelerating, and dark energy, a repulsive energy inherent in space, was proposed to explain the acceleration. Dark energy has since become widely accepted, but it remains unexplained. Accordingly, some scientists continue to work on models that might not require dark energy. Inhomogeneous cosmology falls into this class.
In physical cosmology and astronomy, dark energy is an unknown 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 is the dominant component of 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: 6×10−10 J/m3, 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.
Moshe Carmeli was the Albert Einstein Professor of Theoretical Physics, Ben Gurion University (BGU), Beer Sheva, Israel and President of the Israel Physical Society. He received his D.Sc. from the Technion-Israel Institute of Technology in 1964. He became the first full professor at BGU's new Department of Physics. He did significant theoretical work in the fields of cosmology, astrophysics, general and special relativity, gauge theory, and mathematical physics, authoring 4 books, co-authoring 4 others, and publishing 128 refereed research papers in various journals and forums, plus assorted other publications. He is most notable for his work on gauge theory and his development of the theory of cosmological general relativity, which extends Albert Einstein's theory of general relativity from a four-dimensional spacetime to a five-dimensional space-velocity framework.
Christopher Michael Hirata is an American cosmologist and astrophysicist.
Lucas Lombriser is a Swiss National Science Foundation Professor at the Department of Theoretical Physics, University of Geneva. His research is in Theoretical Cosmology, Dark Energy, and Alternative Theories of Gravity. In 2020 and 2021 Lombriser proposed that the Hubble tension and other discrepancies between cosmological measurements imply significant evidence that we are living in a Hubble Bubble of 250 million light years in diameter which is 20% less dense than the cosmic average and lowers the locally measured cosmic microwave background temperature over its cosmic average. Previously, in 2019, he has proposed a solution to the cosmological constant problem from arguing that Newton's constant varies globally. In 2015 and 2016, Lombriser predicted the measurement of the gravitational wave speed with a neutron star merger and that this would rule out alternative theories of gravity as the cause of the late-time accelerated expansion of our Universe, a prediction that proved true with GW170817. Lombriser is a member of the Romansh-speaking minority in Switzerland.
References
- 1 2 3 4 5 6 7 Marquis Who's Who, "Press Release: Edward John Groth III Presented with the Albert Nelson Marquis Lifetime Achievement Award" (January 31, 2020)
- 1 2 3 4 5 6 7 8 9 10 11 12 Princeton University Office of the Dean, "Edward John Groth III" (downloaded January 6, 2024)
- ↑ Princeton Department of Physics, "Edward Groth" (downloaded January 6, 2024)