Gaurav Khanna | |
---|---|
Born | Chandigarh, India |
Nationality | American |
Occupation(s) | Black hole physicist, supercomputing innovator, academic and researcher |
Title | Professor/Director |
Awards | Fellow of the American Physical Society |
Academic background | |
Education | B. Tech., Electrical Engineering Ph. D., Physics |
Alma mater | Indian Institute of Technology, Kanpur Pennsylvania State University |
Thesis | Binary Black Hole Coalescence: The Close Limit (2000) |
Doctoral advisor | Jorge Pullin |
Academic work | |
Institutions | University of Rhode Island University of Massachusetts Dartmouth |
Website | https://ccr.uri.edu https://web.uri.edu/gravity |
Gaurav Khanna is an Indian-American black hole physicist,supercomputing innovator,academic and researcher. He is a Professor of Physics,and the founding Director of Research Computing and the Center for Computational Research at University of Rhode Island. [1] [2]
Khanna has authored 100 publications. His work is focused in the areas of gravitational physics,computational physics,black holes,and quantum gravity. He has also made contributions in the area of black hole perturbation theory,loop quantum cosmology,singularities and gravitational wave science. He is the creator of the OpenMacGrid, [3] PlayStation 3 Gravity Grid, [4] and developer of open-source software for scientific computing for the Mac. [5] His work has been featured multiple times in newspapers and blogs,including The New York Times , [6] HPCWire, [7] Physics Buzz, [8] The Verge , [9] Forbes , [10] [11] [12] Wired , [13] [14] Scientific American , [15] among others. He was named a Fellow of the American Physical Society in 2021. [16]
Khanna served as a guest editor for a 2018 special issue of IEEE CiSE with a focus on supercomputing. [17]
Khanna studied at Indian Institute of Technology,Kanpur and completed his B. Tech degree in Electrical Engineering in 1995. He then moved to United States and earned his Ph. D. degree in Physics from Pennsylvania State University in 2000. [1]
Beginning in September 2000,he held appointment as an Assistant Professor of Mathematics at Long Island University Southampton. He was then appointed by University of Massachusetts Dartmouth in 2003 as an Assistant Professor of Physics. He was promoted to Associate Professor in 2009,and to Full Professor of Physics in 2015. He is currently a Professor of Physics,and Director of Research Computing at the University of Rhode Island. He is the founding Director of Research Computing and the Center for Computational Research at the university. [1]
His career choices were heavily influenced by his father, [18] Dr. Mohinder P. Khanna,a well-known theoretical particle physicist in Panjab University,India.
Khanna's work is focused in the areas of gravitational physics,computational physics,black holes,and quantum gravity. He has also worked on black hole perturbation theory,loop quantum cosmology,singularities and gravitational wave science.
Khanna is well-known for his research on late-time radiative "tails" in black hole spacetimes,also called "Price tails" named after Richard H. Price. With research collaborators,he was the first to discover the equivalent Price tails formula in the context of (astrophysical,i.e. rotating) Kerr black holes. [19] [20] This formula was later placed on a rigorous mathematical foundation by Aretakis and others. [21]
In another work,Khanna has introduced a reduced-order surrogate model called "EMRISur1dq1e4" for gravitational waveforms. He trained this model on the basis of waveform data generated by point-particle black hole perturbation theory (ppBHPT),and evaluated its applicability for large-mass-ratio and comparable mass-ratio binaries finding that it was unreasonably effective. [22] [23] In his paper published in 2016,he solved the inhomogeneous Teukolsky equation,and focused linearized gravitational waves emitted from a plunge into a nearly extremal Kerr black hole. [24]
Khanna has also studied black hole binaries,and demonstrated that coalescence of two black holes generates gravitational waves that provide information regarding the properties of those black holes and their binary configuration. He further described the ringdown form of final coalescence cycles as a superposition of quasinormal modes in context of the merged remnant black hole. [25]
In his study regarding scientific computation,Khanna introduced a strategy to scale complex hybrid systems,and also discussed a prototype tool which was built over the theorem prover PVS. [26] He also presented techniques that generate information in context of nonlinear dynamical systems,and discussed their applications in terms of automation for polynomial systems using algorithms from computational algebraic geometry. Furthermore,he suggested the application of formal qualitative abstraction approach in terms of nonlinear systems. [27]
Khanna also studied time-domain methods,and proposed their applications in computing gravitational waveforms and fluxes from extreme mass-ratio inspirals. He further explained the computation of low-m modes using the frequency-domain approach,and computation of high-m modes using the time-domain approach. [28]
In the area of scientific computing he is perhaps best known for his innovative work on low-cost supercomputing,making it more accessible to lesser-resourced universities and countries. [29] [30] [31]
While studying singularities,Khanna highlighted the work of Jacobson and Sotiriou in the context of rotating black holes,and then described that if radiative effects can be neglected for the trajectories,that gives rise to naked singularities. He also discussed the significance of the conservative self-force in context of these orbits. [32] He also introduced a class of loop quantizations in terms of anisotropic models including the black hole interior,and studied the refinement process of lattice in context of dynamical changes of the volume. [33]
Khanna published a paper focused on the numerical study of Marolf-Ori singularity inside fast spinning black holes in terms of scalar field or vacuum gravitational perturbations. [34] He also studied how Cauchy horizon singularity inside perturbed Kerr black holes develops an instability that leads to its transformation into a curvature singularity. [35] [36] [37]
Khanna conducted a study in 2019 focused the transient scalar hair,and described the behavior of this nearly extreme black hole hair along with its measurement at future null infinity as a transient phenomenon. [38] [39] Furthermore,he studied about the stability of extreme black holes against linearized gravitational perturbations,and argued that the divergence of ψ4 is a consequence of the choice of a fixed tetrad. [40] [41]
His most recent work on gravitational hair in the context of extremal black holes received significant attention in the community and popular media. [42] [43]
A more complete list is available on Khanna's Google Scholar page. [47]
Khanna has lived in Dartmouth,MA and also in Rhode Island with his wife,April and two daughters Sarah and Rachel.
A black hole is a region of spacetime where gravity is so strong that nothing,including light and other electromagnetic waves,has enough energy to escape it. The theory of general relativity predicts that a sufficiently compact mass can deform spacetime to form a black hole. The boundary of no escape is called the event horizon. Although it has a great effect on the fate and circumstances of an object crossing it,it has no locally detectable features according to general relativity. In many ways,a black hole acts like an ideal black body,as it reflects no light. Moreover,quantum field theory in curved spacetime predicts that event horizons emit Hawking radiation,with the same spectrum as a black body of a temperature inversely proportional to its mass. This temperature is of the order of billionths of a kelvin for stellar black holes,making it essentially impossible to observe directly.
General relativity,also known as the general theory of relativity and 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 generalises 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 matter and radiation are present. The relation is specified by the Einstein field equations,a system of second order partial differential equations.
When there exists at least one causal geodesic that,in the future,extends to an observer either at infinity or to an observer comoving with the collapsing cloud,and in the past terminates at the gravitational singularity,then that singularity is referred to as a naked singularity. In a black hole,the singularity is completely enclosed by a boundary known as the event horizon,inside which the curvature of spacetime caused by the singularity is so strong that light cannot escape. Hence,objects inside the event horizon—including the singularity itself—cannot be observed directly. A naked singularity,by contrast,would be observable from the outside.
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,such as neutron stars as well as in the early stages of the universe moments after the Big Bang.
A wormhole is a hypothetical structure connecting disparate points in spacetime,and is based on a special solution of the Einstein field equations.
The following is a timeline of gravitational physics and general relativity.
In physics,black hole thermodynamics is the area of study that seeks to reconcile the laws of thermodynamics with the existence of black hole event horizons. As the study of the statistical mechanics of black-body radiation led to the development of the theory of quantum mechanics,the effort to understand the statistical mechanics of black holes has had a deep impact upon the understanding of quantum gravity,leading to the formulation of the holographic principle.
Jorge Pullin is an Argentine-American theoretical physicist known for his work on black hole collisions and quantum gravity. He is the Horace Hearne Chair in theoretical Physics at the Louisiana State University.
A gravastar is an object hypothesized in astrophysics by Pawel O. Mazur and Emil Mottola as an alternative to the black hole theory. It has usual black hole metric outside of the horizon,but de Sitter metric inside. On the horizon there is a thin shell of matter. The term "gravastar" is a portmanteau of the words "gravitational vacuum star".
Micro black holes,also called mini black holes or quantum mechanical black holes,are hypothetical tiny black holes,for which quantum mechanical effects play an important role. The concept that black holes may exist that are smaller than stellar mass was introduced in 1971 by Stephen Hawking.
The black hole information paradox is a paradox that appears when the predictions of quantum mechanics and general relativity are combined. The theory of general relativity predicts the existence of black holes that are regions of spacetime from which nothing—not even light—can escape. In the 1970s,Stephen Hawking applied the semi-classical approach of quantum field theory in curved spacetime to such systems and found that an isolated black hole would emit a form of radiation called Hawking radiation. He also argued that the detailed form of the radiation would be independent of the initial state of the black hole,and depend only on its mass,electric charge and angular momentum.
In theoretical physics,quantum field theory in curved spacetime (QFTCS) is an extension of quantum field theory from Minkowski spacetime to a general curved spacetime. This theory uses a semi-classical approach;it treats spacetime as a fixed,classical background,while giving a quantum-mechanical description of the matter and energy propagating through that spacetime. A general prediction of this theory is that particles can be created by time-dependent gravitational fields (multigraviton pair production),or by time-independent gravitational fields that contain horizons. The most famous example of the latter is the phenomenon of Hawking radiation emitted by black holes.
In quantum field theory,a false vacuum is a hypothetical vacuum that is relatively stable,but not in the most stable state possible. 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.
Numerical relativity is one of the branches of general relativity that uses numerical methods and algorithms to solve and analyze problems. To this end,supercomputers are often employed to study black holes,gravitational waves,neutron stars and many other phenomena governed by Einstein's theory of general relativity. A currently active field of research in numerical relativity is the simulation of relativistic binaries and their associated gravitational waves.
A ring singularity or ringularity is the gravitational singularity of a rotating black hole,or a Kerr black hole,that is shaped like a ring.
A Malament–Hogarth (M-H) spacetime,named after David B. Malament and Mark Hogarth,is a relativistic spacetime that possesses the following property:there exists a worldline and an event p such that all events along are a finite interval in the past of p,but the proper time along is infinite. The event p is known as an M-H event.
The TianQin Project is a proposed space-borne gravitational-wave observatory consisting of three spacecraft in Earth orbit. The TianQin project is being led by Professor Luo Jun,President of Sun Yat-sen University,and is based in the university's Zhuhai campus. Construction on project-related infrastructure,which will include a research building,ultra-quiet cave laboratory,and observation center,began in March 2016. The project is estimated to cost 15 billion RMB,with a projected launch date in 2030s. In December 2019,China launched "Tianqin-1,its first satellite for space-based gravitational wave detection."
Carlos O. Lousto is a Distinguished Professor in the School of Mathematical Sciences in Rochester Institute of Technology,known for his work on black hole collisions.
Manuela Campanelli is a distinguished professor of astrophysics and mathematical sciences of the Rochester Institute of Technology,and the director of its Center for Computational Relativity and Gravitation and Astrophysics and Space Sciences Institute for Research Excellence. Her work focuses on the astrophysics of merging black holes and neutron stars,which are powerful sources of gravitational waves,electromagnetic radiation and relativistic jets. This research is central to the new field of multi-messenger astronomy.
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.