Bharat Vishnu Ratra (born 26 January 1960) is an
Indian
Indian or Indians may refer to:
Peoples South Asia
* Indian people, people of Indian nationality, or people who have an Indian ancestor
** Non-resident Indian, a citizen of India who has temporarily emigrated to another country
* South Asia ...
-American
physicist
A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe.
Physicists generally are interested in the root or ultimate caus ...
, theoretical
cosmologist and
astroparticle physicist who is currently a university distinguished professor of
Physics
Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...
at
Kansas State University
Kansas State University (KSU, Kansas State, or K-State) is a public land-grant research university with its main campus in Manhattan, Kansas, United States. It was opened as the state's land-grant college in 1863 and was the first public instit ...
.
He is known for his work on dynamical dark energy and on the quantum-mechanical generation of energy density and magnetic field fluctuations during
inflation
In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reductio ...
.
Biography
Ratra was born in
Bombay (Mumbai)
Mumbai (, ; also known as Bombay — the official name until 1995) is the capital city of the Indian state of Maharashtra and the ''de facto'' financial centre of India. According to the United Nations, as of 2018, Mumbai is the second-m ...
. He graduated with a Master of Science in physics from the
Indian Institute of Technology Delhi
The Indian Institute of Technology, Delhi is a public institute of technology located in New Delhi, India. It is one of the 23 IITs created to be Centres of Excellence for training, research and development in science, engineering and technolo ...
in 1982 and completed his doctorate in physics at
Stanford University
Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...
in 1986 under the supervision of
Leonard Susskind
Leonard Susskind (; born June 16, 1940)his 60th birthday was celebrated with a special symposium at Stanford University.in Geoffrey West's introduction, he gives Suskind's current age as 74 and says his birthday was recent. is an American physicis ...
and
Michael Peskin Michael Edward Peskin (born October 27, 1951, Philadelphia) is an American theoretical physicist. He was an undergraduate at Harvard University and obtained his Ph.D. in 1978 at Cornell University studying under Kenneth Wilson. He was a Junior Fell ...
.
Ratra was a postdoctoral fellow at the
Stanford Linear Accelerator Center
SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center,
is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...
,
Princeton University
Princeton University is a private university, private research university in Princeton, New Jersey. Founded in 1746 in Elizabeth, New Jersey, Elizabeth as the College of New Jersey, Princeton is the List of Colonial Colleges, fourth-oldest ins ...
, the
California Institute of Technology and the
Massachusetts Institute of Technology
The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the ...
. He joined Kansas State University in 1996 as an assistant professor of physics. He was promoted to associate professor in 2001 and professor in 2004.
Academics and research
Ratra has worked in a number of areas of cosmology and astroparticle and early universe physics.
In 1988, Ratra and
Jim Peebles of Princeton University proposed the first dynamical
dark energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univer ...
scalar field
In mathematics and physics, a scalar field is a function (mathematics), function associating a single number to every point (geometry), point in a space (mathematics), space – possibly physical space. The scalar may either be a pure Scalar ( ...
, or
quintessence
Quintessence, or fifth essence, may refer to:
Cosmology
* Aether (classical element), in medieval cosmology and science, the fifth element that fills the universe beyond the terrestrial sphere
* Quintessence (physics), a hypothetical form of da ...
, model.
Dark energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univer ...
is the leading candidate for the mechanism that is responsible for causing the observed accelerated cosmological expansion.
Ratra and his students and collaborators have pioneered measurements of the redshift of the transition between an earlier epoch when cosmological expansion decelerated because dark and baryonic (ordinary) matter dominated the cosmological energy budget and the current epoch where the cosmological expansion accelerates because dark energy dominates the current cosmological energy budget.
Ratra and his students and collaborators have developed new cosmological probes and used these in conjunction with better-established ones to measure the Hubble constant (
Hubble's law), the geometry of space (
Shape of the universe
The shape of the universe, in physical cosmology, is the local and global geometry of the universe. The local features of the geometry of the universe are primarily described by its curvature, whereas the topology of the universe describes gen ...
), and
dark energy
In physical cosmology and astronomy, dark energy is an unknown form of energy that affects the universe on the largest scales. The first observational evidence for its existence came from measurements of supernovas, which showed that the univer ...
dynamics.
Ratra's early universe research includes the first consistent semi-classical computation of the spectrum of energy density perturbations from
inflation
In economics, inflation is an increase in the general price level of goods and services in an economy. When the general price level rises, each unit of currency buys fewer goods and services; consequently, inflation corresponds to a reductio ...
. He collaborated with
Willy Fischler
Willy Fischler (born 1949 in Antwerp, Belgium) is a theoretical physicist. He is the Jane and Roland Blumberg Centennial Professor of Physics at the University of Texas at Austin, where he is affiliated with the Weinberg theory group. He is al ...
of the University of Texas at Austin and
Leonard Susskind
Leonard Susskind (; born June 16, 1940)his 60th birthday was celebrated with a special symposium at Stanford University.in Geoffrey West's introduction, he gives Suskind's current age as 74 and says his birthday was recent. is an American physicis ...
of Stanford University on this computation. He has also computed the power spectrum of energy density perturbations in non-spatially-flat inflation models.
Ratra also proposed the first inflation model that can generate, from quantum fluctuations, a large-enough primordial cosmological magnetic field to be able to explain observed galactic magnetic fields.
[B. Ratra, "Cosmological `seed' magnetic field from inflation", ''Astrophys. J.'' 391, L1 (1992) (PDF)]
Honours
*
National Science Foundation
The National Science Foundation (NSF) is an independent agency of the United States government that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National I ...
CAREER award (1999)
* Fellow of the
American Physical Society
The American Physical Society (APS) is a not-for-profit membership organization of professionals in physics and related disciplines, comprising nearly fifty divisions, sections, and other units. Its mission is the advancement and diffusion of k ...
(2002)
* Fellow of the
American Association for the Advancement of Science
The American Association for the Advancement of Science (AAAS) is an American international non-profit organization with the stated goals of promoting cooperation among scientists, defending scientific freedom, encouraging scientific respons ...
(2005)
* Olin Petefish Award in Basic Science (2017)
* Fellow of the
American Astronomical Society
The American Astronomical Society (AAS, sometimes spoken as "double-A-S") is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the adv ...
(2023)
References
External links
13 February 2017 University of Kansas Colloquium: Dark Energy: constant or time variable? (... and other open questions)5 November 2019 Kansas State University Colloquium: The Accelerating Expanding Universe: Dark Matter, Dark Energy, and Einstein's Cosmological Constant, or Why Jim Peebles was Awarded Half of the 2019 Physics Nobel Prize2 February 2023 Canadian Institute for Theoretical Astrophysics Seminar: Spatial Curvature, Dark Energy Dynamics, Neither, or Both?
{{DEFAULTSORT:Ratra, Bharat
1960 births
Living people
21st-century American physicists
20th-century Indian physicists
American people of Indian descent
Scientists from Mumbai
Cosmologists
Stanford University alumni
Kansas State University faculty
IIT Delhi alumni
Fellows of the American Physical Society
Fellows of the American Association for the Advancement of Science