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 ...

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

dynamics. Ratra's early universe research includes the first consistent semi-classical computation of the spectrum of energy density perturbations from

. 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

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 Prize

2 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