Anupam Mazumdar | |
---|---|
Born | Anupam Mazumdar |
Awards | JSPS Award, Japan, Inlaks Fellowship, India |
Scientific career | |
Fields | Physics, Cosmology, Inflation (Cosmology), Quantum Gravity |
Institutions | University of Sussex, Imperial College, London, ICTP, McGill University, Niels Bohr Institute, Lancaster University, University of Groningen |
Doctoral advisor | Andrew R. Liddle |
Website | http://www.rug.nl/staff/anupam.mazumdar/ |
Anupam Mazumdar is a theoretical physicist at the University of Groningen [1] specializing in cosmology and quantum gravity.
Together with Sougato Bose, Mazumdar has proposed a bonafide test for the existence of the graviton in a table-top experiment, via witnessing gravitationally-mediated entanglement between two macroscopic superpositions of masses. [2] A positive test of this phenomenon would establish experimentally that gravity is quantum mechanical in nature, and establish the existence of the graviton. [3] The test crucially depends on the quantum nature of gravity, creating non-classical states of matter, and local operation and quantum communication (LOQC). [4]
He has previously been affiliated to the Higgs Centre, at the University of Edinburgh, [5] and the Discovery Center at the Niels Bohr Institute, Copenhagen. [6]
His work has focused on multi field theories of inflation, such as assisted inflation, [7] visible sector inflation such as MSSM inflation. [8] He has worked on the ghost-free and singularity-free construction of infinite derivative theories of gravity, [9] which can potentially resolve the Schwarzschild singularity for mini black holes, yielding a non-singular compact object without event horizon, and cosmological singularities. He has also conjectured with Koshelev that astrophysical black hole has no curvature singularity and devoid of an event horizon, [10] in infinite derivative theories of gravity, because the scale of non-locality in gravitational interaction can engulf the gravitational radius of the compact object. At time scales and at distances below the effective scale of non-locality the gravitational interaction weakens sufficiently enough that a finite pressure from normal matter satisfying null, strong and weak energy conditions can avoid forming blackhole with event horizon and cosmological singularities.
General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time, or four-dimensional spacetime. In particular, the curvature of spacetime is directly related to the energy and momentum of whatever present matter and radiation. The relation is specified by the Einstein field equations, a system of second-order partial differential equations.
In theories of quantum gravity, the graviton is the hypothetical elementary particle that mediates the force of gravitational interaction. There is no complete quantum field theory of gravitons due to an outstanding mathematical problem with renormalization in general relativity. In string theory, believed by some to be a consistent theory of quantum gravity, the graviton is a massless state of a fundamental string.
In general relativity, a naked singularity is a hypothetical gravitational singularity without an event horizon.
Quantum gravity (QG) is a field of theoretical physics that seeks to describe gravity according to the principles of quantum mechanics. It deals with environments in which neither gravitational nor quantum effects can be ignored, such as in the vicinity of black holes or similar compact astrophysical objects, as well as in the early stages of the universe moments after the Big Bang.
A gravitational singularity, spacetime singularity, or simply singularity, is a theoretical condition in which gravity is predicted to be so intense that spacetime itself would break down catastrophically. As such, a singularity is by definition no longer part of the regular spacetime and cannot be determined by "where" or "when". Gravitational singularities exist at a junction between general relativity and quantum mechanics; therefore, the properties of the singularity cannot be described without an established theory of quantum gravity. Trying to find a complete and precise definition of singularities in the theory of general relativity, the current best theory of gravity, remains a difficult problem. A singularity in general relativity can be defined by the scalar invariant curvature becoming infinite or, better, by a geodesic being incomplete.
The Penrose–Hawking singularity theorems are a set of results in general relativity that attempt to answer the question of when gravitation produces singularities. The Penrose singularity theorem is a theorem in semi-Riemannian geometry and its general relativistic interpretation predicts a gravitational singularity in black hole formation. The Hawking singularity theorem is based on the Penrose theorem and it is interpreted as a gravitational singularity in the Big Bang situation. Penrose shared half of the Nobel Prize in Physics in 2020 "for the discovery that black hole formation is a robust prediction of the general theory of relativity".
The Big Bounce hypothesis is a cosmological model for the origin of the known universe. It was originally suggested as a phase of the cyclic model or oscillatory universe interpretation of the Big Bang, where the first cosmological event was the result of the collapse of a previous universe. It receded from serious consideration in the early 1980s after inflation theory emerged as a solution to the horizon problem, which had arisen from advances in observations revealing the large-scale structure of the universe.
In astrophysics, the gravastar is an object hypothesized in a 2006 paper by Pawel O. Mazur and Emil Mottola as an alternative to the black hole theory. It has the usual black hole metric outside of the horizon, but de Sitter metric inside. On the horizon there is a thin shell of matter. This solution to the Einstein equations is stable and has no singularities. Further theoretical considerations of gravastars include the notion of a nestar.
In particle physics, the hypothetical dilaton particle is a particle of a scalar field that appears in theories with extra dimensions when the volume of the compactified dimensions varies. It appears as a radion in Kaluza–Klein theory's compactifications of extra dimensions. In Brans–Dicke theory of gravity, Newton's constant is not presumed to be constant but instead 1/G is replaced by a scalar field and the associated particle is the dilaton.
In theoretical physics, the hierarchy problem is the problem concerning the large discrepancy between aspects of the weak force and gravity. There is no scientific consensus on why, for example, the weak force is 1024 times stronger than gravity.
In theoretical physics, geometrodynamics is an attempt to describe spacetime and associated phenomena completely in terms of geometry. Technically, its goal is to unify the fundamental forces and reformulate general relativity as a configuration space of three-metrics, modulo three-dimensional diffeomorphisms. The origin of this idea can be found in an English mathematician William Kingdon Clifford's works. This theory was enthusiastically promoted by John Wheeler in the 1960s, and work on it continues in the 21st century.
In quantum field theory, a false vacuum is a hypothetical vacuum state that is locally stable but does not occupy the most stable possible ground state. In this condition it is called metastable. It may last for a very long time in this state, but could eventually decay to the more stable one, an event known as false vacuum decay. The most common suggestion of how such a decay might happen in our universe is called bubble nucleation – if a small region of the universe by chance reached a more stable vacuum, this "bubble" would spread.
Induced gravity is an idea in quantum gravity that spacetime curvature and its dynamics emerge as a mean field approximation of underlying microscopic degrees of freedom, similar to the fluid mechanics approximation of Bose–Einstein condensates. The concept was originally proposed by Andrei Sakharov in 1967.
Loop quantum cosmology (LQC) is a finite, symmetry-reduced model of loop quantum gravity (LQG) that predicts a "quantum bridge" between contracting and expanding cosmological branches.
In physics the Einstein-aether theory, also called aetheory, is the name coined in 2004 for a modification of general relativity that has a preferred reference frame and hence violates Lorentz invariance. These generally covariant theories describes a spacetime endowed with both a metric and a unit timelike vector field named the aether. The aether in this theory is "a Lorentz-violating vector field" unrelated to older luminiferous aether theories; the "Einstein" in the theory's name comes from its use of Einstein's general relativity equation.
Analog models of gravity are attempts to model various phenomena of general relativity using other physical systems such as acoustics in a moving fluid, superfluid helium, or Bose–Einstein condensate; gravity waves in water; and propagation of electromagnetic waves in a dielectric medium. These analogs serve to provide new ways of looking at problems, permit ideas from other realms of science to be applied, and may create opportunities for practical experiments within the analog that can be applied back to the source phenomena.
In physics, a tachyonic field, or simply tachyon, is a quantum field with an imaginary mass. Although tachyonic particles are a purely hypothetical concept that violate a number of essential physical principles, at least one field with imaginary mass, the Higgs field, is believed to exist. Under no circumstances do any excitations of tachyonic fields ever propagate faster than light—the presence or absence of a tachyonic (imaginary) mass has no effect on the maximum velocity of signals, and so unlike faster-than-light particles there is no violation of causality. Tachyonic fields play an important role in physics and are discussed in popular books.
In theoretical physics, the problem of time is a conceptual conflict between quantum mechanics and general relativity. Quantum mechanics regards the flow of time as universal and absolute, whereas general relativity regards the flow of time as malleable and relative. This problem raises the question of what time really is in a physical sense and whether it is truly a real, distinct phenomenon. It also involves the related question of why time seems to flow in a single direction, despite the fact that no known physical laws at the microscopic level seem to require a single direction.
Infinite derivative gravity is a theory of gravity which attempts to remove cosmological and black hole singularities by adding extra terms to the Einstein–Hilbert action, which weaken gravity at short distances.
Hermann Nicolai is a German theoretical physicist and director emeritus at the Max Planck Institute for Gravitational Physics in Potsdam-Golm.