B. M. Udgaonkar Eminent Scientist & Educationist
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Francis E. Low
NATIONAL ACADEMY OF SCIENCES F R A N C I S E . L OW 1 9 2 1 – 2 0 0 7 A Biographical Memoir by DAVID KAISER AND MARC A . K A S T N E R Any opinions expressed in this memoir are those of the authors and do not necessarily reflect the views of the National Academy of Sciences. Biographical Memoir COPYRIGHT 2010 NATIONAL ACADEMY OF SCIENCES WASHINGTON, D.C. Courtesy of MIT Archives. FRANCIS E. LOW October 27, 1921–February 16, 2007 BY DAVID KAISER AND MARC A . K ASTNER RANCIS E. LOW, A MEMBER OF THE NATIONAL ACADEMY OF SCIENCES Fsince 1967, died on February 16, 2007, in Haverford, Pennsylvania. His career exemplified the maturing of theo- retical physics in the United States during the years after World War II. Low also experienced some of the new roles for physicists, from organized political engagement and consulting on national security issues to high-level university administration. One of Low’s landmark articles helped to lay the groundwork for the renormalization-group approach in quantum field theory, a seminal technique in condensed- matter and particle physics. He also contributed influential approximation techniques for treating particle scattering. EARLY YEARS Low was an only child, who lived near Washington Square Park in Greenwich Village. His mother’s parents were physi- cians and socialists. In fact, his grandfather helped found the Socialist Party of America. His mother also became a doctor. She made house calls at night in Greenwich Village until she turned 80, treating patients such as anthropolo- gist Margaret Mead. -
Covariant Phase Space for Gravity with Boundaries: Metric Vs Tetrad Formulations
Covariant phase space for gravity with boundaries: metric vs tetrad formulations J. Fernando Barbero G.c,d Juan Margalef-Bentabola,c Valle Varob,c Eduardo J.S. Villaseñorb,c aInstitute for Gravitation and the Cosmos and Physics Department. Penn State University. PA 16802, USA. bDepartamento de Matemáticas, Universidad Carlos III de Madrid. Avda. de la Universidad 30, 28911 Leganés, Spain. cGrupo de Teorías de Campos y Física Estadística. Instituto Gregorio Millán (UC3M). Unidad Asociada al Instituto de Estructura de la Materia, CSIC, Madrid, Spain. dInstituto de Estructura de la Materia, CSIC, Serrano 123, 28006, Madrid, Spain E-mail: [email protected], [email protected], [email protected], [email protected] Abstract: We use covariant phase space methods to study the metric and tetrad formula- tions of General Relativity in a manifold with boundary and compare the results obtained in both approaches. Proving their equivalence has been a long-lasting problem that we solve here by using the cohomological approach provided by the relative bicomplex framework. This setting provides a clean and ambiguity-free way to describe the solution spaces and associated symplectic structures. We also compute several relevant charges in both schemes and show that they are equivalent, as expected. arXiv:2103.06362v2 [gr-qc] 14 Jun 2021 Contents I Introduction1 II The geometric arena2 II.1 M as a space-time2 II.2 From M-vector fields to F-vector fields3 II.3 CPS-Algorithm4 IIIGeneral Relativity in terms of metrics5 IV General relativity in terms of tetrads8 V Metric vs Tetrad formulation 13 V.1 Space of solutions 13 V.2 Presymplectic structures 14 VI Conclusions 15 A Ancillary material 16 A.1 Mathematical background 16 A.2 Some computations in the metric case 19 A.3 Some tetrad computations 21 Bibliography 22 I Introduction Space-time boundaries play a prominent role in classical and quantum General Relativity (GR). -
Pos(Rio De Janeiro 2012)002 † ∗ [email protected] Speaker
Loop Quantum Gravity and the Very Early Universe PoS(Rio de Janeiro 2012)002 Abhay Ashtekar∗† Institute for Gravitational Physics and Geometry, Physics Department, Penn State, University Park, PA 16802, U.S.A. E-mail: [email protected] This brief overview is addressed to beginning researchers. It begins with a discussion of the distinguishing features of loop quantum gravity, then illustrates the type of issues that must be faced by any quantum gravity theory, and concludes with a brief summary of the status of these issues in loop quantum gravity. For concreteness the emphasis is on cosmology. Since several introductory as well as detailed reviews of loop quantum gravity are already available in the literature, the focus is on explaining the overall viewpoint and providing a short bibliography to introduce the interested reader to literature. 7th Conference Mathematical Methods in Physics - Londrina 2012, 16 to 20 April 2012 Rio de Janeiro, Brazil ∗Speaker. †A footnote may follow. c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence. http://pos.sissa.it/ Loop Quantum Gravity Abhay Ashtekar Loop quantum gravity (LQG) is a non-perturbative approach aimed at unifying general rela- tivity and quantum physics. Its distinguishing features are: i) Background independence, and, ii) Underlying unity of the mathematical framework used to describe gravity and the other three basic forces of nature. It is background independent in the sense that there are no background fields, not even a space-time metric. All fields —whether they represent matter constituents, or gauge fields that mediate fundamental forces between them, or space- time geometry itself— are treated on the same footing. -
Scaling Laws in Particle Physics and Astrophysics
SCALING LAWS IN PARTICLE PHYSICS AND ASTROPHYSICS RUDOLF MURADYAN Dedicated to the Golden Jubilee (1961-2011) of publication of the article by Geoffrey Chew and Steven Frautschi in Phys. Rev. Lett. 7, 394, 1961, where a celebrated scaling law J m2 has been conjectured for spin/mass dependence of hadrons. G. Chew S. Frautschi 1. INTRODUCTION: WHAT IS SCALING? Any polynomial power law f() x c xn , where constant c has a dimension dim f dimc (dimx )n exhibits the property of scaling or scale invariance. Usually n is called scaling exponent. The word scaling express the fact that function f is shape-invariant with respect to the dilatation transformation x x f ( x) c ( x)n n f() x and this transformation preserves the shape of function f . We say, following Leonhard Euler, that f is homogeneous of degree “n” if for any value of parameter f ( x) n f() x . Differentiating this relation with respect to and putting 1we obtain simple differential equation x f() x n f() x solution of which brings back to the polynomial power scaling law. There are tremendously many different scaling laws in Nature. The most important of them can be revealed by Google search of scaling site:nobelprize.org in the official site of Nobel Foundation, where nearly 100 results appears. Ten of them are shown below: 1. Jerome I. Friedman - Nobel Lecture 2. Daniel C. Tsui - Nobel Lecture 3. Gerardus 't Hooft - Nobel Lecture 4. Henry W. Kendall - Nobel Lecture 5. Pierre-Gilles de Gennes - Nobel Lecture 6. Jack Steinberger - Nobel Lecture 7. -
BEYOND SPACE and TIME the Secret Network of the Universe: How Quantum Geometry Might Complete Einstein’S Dream
BEYOND SPACE AND TIME The secret network of the universe: How quantum geometry might complete Einstein’s dream By Rüdiger Vaas With the help of a few innocuous - albeit subtle and potent - equations, Abhay Ashtekar can escape the realm of ordinary space and time. The mathematics developed specifically for this purpose makes it possible to look behind the scenes of the apparent stage of all events - or better yet: to shed light on the very foundation of reality. What sounds like black magic, is actually incredibly hard physics. Were Albert Einstein alive today, it would have given him great pleasure. For the goal is to fulfil the big dream of a unified theory of gravity and the quantum world. With the new branch of science of quantum geometry, also called loop quantum gravity, Ashtekar has come close to fulfilling this dream - and tries thereby, in addition, to answer the ultimate questions of physics: the mysteries of the big bang and black holes. "On the Planck scale there is a precise, rich, and discrete structure,” says Ashtekar, professor of physics and Director of the Center for Gravitational Physics and Geometry at Pennsylvania State University. The Planck scale is the smallest possible length scale with units of the order of 10-33 centimeters. That is 20 orders of magnitude smaller than what the world’s best particle accelerators can detect. At this scale, Einstein’s theory of general relativity fails. Its subject is the connection between space, time, matter and energy. But on the Planck scale it gives unreasonable values - absurd infinities and singularities. -
Laudatio for Professor Abhay Ashtekar
Laudatio for Professor Abhay Ashtekar Professor Ashtekar is a remarkable ¯gure in the ¯eld of Ein- stein's gravity. This being the Einstein Year and, moreover, the World Year of Physics, one can hardly think of anyone more ¯tting to be honoured for his research and his achievements { achievements that have influenced the most varied aspects of gravitational theory in a profound way. Prof. Ashtekar is the Eberly Professor of Physics and the Di- rector of the Institute for Gravitational Physics and Geometry at Penn State University in the United States. His research in gravitational theory is notable for its breadth, covering quantum gravity and generalizations of quantum mechanics, but also clas- sical general relativity, the mathematical theory of black holes and gravitational waves. Our view of the world has undergone many revisions in the past, two of which, arguably the most revolutionary, were ini- tiated by Einstein in his annus mirabilis, 1905. For one thing, the theory of special relativity turned our notion of space and time on its ear for speeds approaching that of light. At the same time, Einstein's explanation of the photoelectric e®ect heralded the coming of quantum theory. Many of the best minds in theo- retical physics, including Einstein himself, have been trying for years to ¯nd a uni¯ed theory of relativity and quantum theory. Such a theory, often called quantum gravity, could, for example, provide an explanation for the initial moments of our universe just after the big bang. Especially noteworthy is Prof. Ashtekar's work on the canon- ical quantization of gravitation, which is based upon a reformu- lation of Einstein's ¯eld equations that Ashtekar presented 1986. -
MATTERS of GRAVITY, a Newsletter for the Gravity Community, Number 3
MATTERS OF GRAVITY Number 3 Spring 1994 Table of Contents Editorial ................................................... ................... 2 Correspondents ................................................... ............ 2 Gravity news: Open Letter to gravitational physicists, Beverly Berger ........................ 3 A Missouri relativist in King Gustav’s Court, Clifford Will .................... 6 Gary Horowitz wins the Xanthopoulos award, Abhay Ashtekar ................ 9 Research briefs: Gamma-ray bursts and their possible cosmological implications, Peter Meszaros 12 Current activity and results in laboratory gravity, Riley Newman ............. 15 Update on representations of quantum gravity, Donald Marolf ................ 19 Ligo project report: December 1993, Rochus E. Vogt ......................... 23 Dark matter or new gravity?, Richard Hammond ............................. 25 Conference Reports: Gravitational waves from coalescing compact binaries, Curt Cutler ........... 28 Mach’s principle: from Newton’s bucket to quantum gravity, Dieter Brill ..... 31 Cornelius Lanczos international centenary conference, David Brown .......... 33 Third Midwest relativity conference, David Garfinkle ......................... 36 arXiv:gr-qc/9402002v1 1 Feb 1994 Editor: Jorge Pullin Center for Gravitational Physics and Geometry The Pennsylvania State University University Park, PA 16802-6300 Fax: (814)863-9608 Phone (814)863-9597 Internet: [email protected] 1 Editorial Well, this newsletter is growing into its third year and third number with a lot of strength. In fact, maybe too much strength. Twelve articles and 37 (!) pages. In this number, apart from the ”traditional” research briefs and conference reports we also bring some news for the community, therefore starting to fulfill the original promise of bringing the gravity/relativity community closer together. As usual I am open to suggestions, criticisms and proposals for articles for the next issue, due September 1st. Many thanks to the authors and the correspondents who made this issue possible. -
150 Abhay Ashtekar
ICTS PUBLIC LECTURE BIG BANG, BLACK HOLES AND GRAVITATIONAL WAVES Illustrations of Paradigm Shifts in Fundamental Science Big Bang, Black Holes and Gravitational Waves now appear as compelling – even obvious – consequences of general relativity. Therefore, it may seem surprising that none of these ideas were readily accepted. Not only was there considerable debate, but in fact leading figures were often arguing on what turned out to be the “wrong side” of history. These developments provide excellent lessons for younger researchers on how science un-folds. Paradigm shifts in science occur when younger researchers have the courage not to accept ideas merely because they are mainstream; patience to systematically develop novel avenues they deeply believe in; and maturity to accept that a variety of factors – not all logical or even science related – can drive or slow down scientific progress. ABHAY ASHTEKAR Pennsylvania State University Abhay Ashtekar is the Eberly Professor of Physics and the Director of the Institute for Gravitational Physics and Geometry at Pennsylvania State University. His research interests span different aspects of General Relativity, Quantum Gravity and Black Holes. The recipient of the Einstein Prize and the Senior Research Prize of the Humboldt Foundation, his work is widely recognized. He is an elected member of the US National Academy of Sciences, Elected Fellow of the American Association for Advancement of Science, American Physical Society and Honorary Fellow of the Indian Academy of Sciences, and has served as the president of International Society for General Relativity and Gravitation. 4 pm, 21 August, 2019 ICTS, Bengaluru Register online https://bit.ly/AbhayAshtekar BG Image – Frame from a simulation of the merger of two black holes and the resulting emission of gravitational radiation (colored fields). -
AC2 Report to IUPAP 2016.Pages
Report of Affiliated Commission AC.2 for 2015-16 submitted by Beverly K. Berger, Secretary The principal event of the year for the International Society on General Relativity and Gravitation (AC2) was the triennial GR conference. The 21st International Conference on General Relativity and Gravitation, GR21, was held 10 – 15 July 2016 at Columbia University. The scientific highlights of the meeting were talks and activities related to the first direct detection of gravitational waves by the LIGO Scientific Collaboration and the Virgo Collaboration—a momentous celebration of the Centennial of Einstein's first presentation of general relativity in November 1915. Approximately 650 registered participants attended the meeting. Sponsorship from IUPAP for this meeting, and AC2's own limited funds, assisted some of these participants. As usual, the conference had plenary talks in the morning, covering the whole field of AC2's interests. In the afternoons there were parallel contributed papers and poster sessions. There were 15 plenary talks (5 of the speakers being women) and 17 parallel sessions (7 of the chairs being women). Abstracts of all submissions became available online1 after the meeting. The abstracts of all parallel session talks and posters and the slides from the parallel session talks are available on the conference website.2 Slides from the plenary talks will be available soon. During the meeting, several prize winners were honored by AC2 and GWIC (WG11): The IUPAP Young Scientist Prize in General Relativity and Gravitation was first awarded at GR20 in 2013. The three winners since then, Jorge Santos, Stanford University and Cambridge University (2014), Nicolas Yunes, Montana State University (2015), and Ivan Agullo, Louisiana State University (2016) were recognized at the meeting. -
Books in Brief Early Leader, Swayed by the Mistaken Belief That Others’ Choices Tell Them About Standard
BOOKS & ARTS COMMENT observed differences in success — judged by popularity or sales, for example — follow from network effects. People rush to buy an Books in brief early leader, swayed by the mistaken belief that others’ choices tell them about standard. Quantum Space This results in huge differences in outcome Jim Baggott OXFORD UNIV. PRESS (2018) that have nothing at all to do with quality. Prolific physics writer Jim Baggott is back with a terrific page-turner That phenomenon is the subject of the second on loop quantum gravity (LQG) — the theory posited as a solution law: “Performance is bounded, but success is to that chasm in physics between quantum mechanics and the unbounded.” Take the top 100 wines entered general theory of relativity. Baggott digs into the how and why of into a competition. Their true differences in what LQG might reveal about “space, time and the universe”, tracing quality, for example in clarity or varietal char- its evolution through the work of Abhay Ashtekar, Lee Smolin, acter, are generally small: they’re all produced Carlo Rovelli and others, to its current implications for, say, the physics by top winemakers using similar technology. of black holes. Baggott masterfully tenderizes the scientific chewiness Yet one wine, because of the amplifying power and is careful not to over-egg what is, after all, a work in progress. of social networks, might enjoy orders of magnitude more sales than others. Social scientists have known about such The Republican Reversal effects for decades, although research by James Morton Turner and Andrew C. Isenberg HARVARD UNIV. -
The Strong and Weak Senses of Theory-Ladenness of Experimentation: Theory-Driven Versus Exploratory Experiments in the History of High-Energy Particle Physics
[Accepted for Publication in Science in Context] The Strong and Weak Senses of Theory-Ladenness of Experimentation: Theory-Driven versus Exploratory Experiments in the History of High-Energy Particle Physics Koray Karaca University of Wuppertal Interdisciplinary Centre for Science and Technology Studies (IZWT) University of Wuppertal Gaußstr. 20 42119 Wuppertal, Germany [email protected] Argument In the theory-dominated view of scientific experimentation, all relations of theory and experiment are taken on a par; namely, that experiments are performed solely to ascertain the conclusions of scientific theories. As a result, different aspects of experimentation and of the relation of theory to experiment remain undifferentiated. This in turn fosters a notion of theory- ladenness of experimentation (TLE) that is too coarse-grained to accurately describe the relations of theory and experiment in scientific practice. By contrast, in this article, I suggest that TLE should be understood as an umbrella concept that has different senses. To this end, I introduce a three-fold distinction among the theories of high-energy particle physics (HEP) as background theories, model theories and phenomenological models. Drawing on this categorization, I contrast two types of experimentation, namely, “theory-driven” and “exploratory” experiments, and I distinguish between the “weak” and “strong” senses of TLE in the context of scattering experiments from the history of HEP. This distinction enables to identify the exploratory character of the deep-inelastic electron-proton scattering experiments— performed at the Stanford Linear Accelerator Center (SLAC) between the years 1967 and 1973—thereby shedding light on a crucial phase of the history of HEP, namely, the discovery of “scaling”, which was the decisive step towards the construction of quantum chromo-dynamics (QCD) as a gauge theory of strong interactions. -
Emergence of Time in Loop Quantum Gravity∗
Emergence of time in Loop Quantum Gravity∗ Suddhasattwa Brahma,1y 1 Center for Field Theory and Particle Physics, Fudan University, 200433 Shanghai, China Abstract Loop quantum gravity has formalized a robust scheme in resolving classical singu- larities in a variety of symmetry-reduced models of gravity. In this essay, we demon- strate that the same quantum correction which is crucial for singularity resolution is also responsible for the phenomenon of signature change in these models, whereby one effectively transitions from a `fuzzy' Euclidean space to a Lorentzian space-time in deep quantum regimes. As long as one uses a quantization scheme which re- spects covariance, holonomy corrections from loop quantum gravity generically leads to non-singular signature change, thereby giving an emergent notion of time in the theory. Robustness of this mechanism is established by comparison across large class of midisuperspace models and allowing for diverse quantization ambiguities. Con- ceptual and mathematical consequences of such an underlying quantum-deformed space-time are briefly discussed. 1 Introduction It is not difficult to imagine a mind to which the sequence of things happens not in space but only in time like the sequence of notes in music. For such a mind such conception of reality is akin to the musical reality in which Pythagorean geometry can have no meaning. | Tagore to Einstein, 1920. We are yet to come up with a formal theory of quantum gravity which is mathematically consistent and allows us to draw phenomenological predictions from it. Yet, there are widespread beliefs among physicists working in fundamental theory regarding some aspects of such a theory, once realized.