An interesting interview with Carver Mead, author of the (unconventional) Collective Electrodynamics: Quantum Foundations of Electromagnetism.
Archive for January, 2009
Most of us do elementary-particle physics neither because of the intrinsic interestingness of the phenomena that we study, nor because of the practical importance of what we learn, but because we are pursuing a reductionist vision. All of the properties of ordinary matter are what they are because of the principles of atomic and nuclear physics, which are what they are because of the rules of the Standard Model of elementary particles, which are what they are because…well, we don’t know, this is the reductionist frontier, which we are currently exploring.
Weinberg, From BCS to the LHC
THE SCIENCE AND PHILOSOPHY OF UNCONVENTIONAL COMPUTING (SPUC09)
Cambridge (UK), March 23-25, 2009
SECOND CALL FOR PAPERS
We welcome submissions on topics normally classified under ‘natural computing’ or ‘unconventional computing’ or ‘hypercomputing’ including (but not restricted to) quantum computing, relativistic computing, biology-based computing, analogue computing, and also submissions on the philosophical implications of these new fields for topics including (but again not restricted to) philosophy of mind, philosophy of mathematics, the Church-Turing thesis.
Each presentation should last no more than 30 minutes; a further 10 minutes will be allowed for discussion.
Those wishing to make a presentation should submit by email a 250-word abstract of their paper to Mark Hogarth (firstname.lastname@example.org); enquiries to the same.
Registration fee (yet to be fixed) will be around £100.
Student bursaries are available.
Conference website: http://web.mac.com/mhogarth/Site/SPUC_Conference.html
Mark Hogarth (Cambridge, UK)
CONFIRMED INVITED SPEAKERS
Selmer Brinsjord (New York, USA))
Jeff Barrett (Irvine, USA)
Philip Welch (Bristol, UK)
Tim Button (Harvard, USA)
Cristian Calude (Auckland, New Zealand))
István Németi (Budapest, Hungry)
Benjamin Wells (San Francisco, USA)
Hajnal Andréka (Budapest, Hungry)
Apostolos Syropoulos (Xanthi, Greece)
Susan Stepney (York, UK)
Bruce MacLennan (Tennessee, USA)
Peter Kugel (Boston, USA)
Mark Sprevak (Cambridge, UK)
Selim Akl (Kingston, Canada)
José Félix Costa (Swansea, UK)
Mike Stannett (Sheffield, UK)
John Tucker (Swansea, UK)
Barry Cooper (Leeds, UK)
Sponsored by EPSRC through HyperNet (the Hypercomputation Research Network, EP/E064183/1)
I am writing to ask for your assistance in drawing the attention of exceptional, highly motivated students to the Perimeter Scholars International (PSI) program.
PSI is an innovative, Masters level course designed to prepare students for cutting-edge research in theoretical physics. It provides a broad overview, allowing students to choose their preferred specialisation, and extensive tuition in formulating and solving interesting problems.
The due date for applications is February 1st: applications received after this date may still be considered but only as long as places remain available.
A number of outstanding lecturers have already signed up to teach, including for example Yakir Aharonov, Phil Anderson, Matt Choptuik, Nima Arkani-Hamed, John Cardy, Ruth Gregory, Michael Peskin, Sid Redner, Xiao-Gang Wen, and a number of Perimeter Institute research faculty. They will be supported by full-time tutors dedicated to the course.
All accepted students will be fully supported.
For further details, see www.perimeterscholars.org.
Thank you in advance for helping us to make this exciting opportunity known as widely as possible.
With my best wishes,
Perimeter Institute for Theoretical Physics
Waterloo, Ontario, Canada
Here is a picture that my 9 years-old son took of us (from left to right: Sabine, Stefan, me and Fabiano, my hunsband):
Thanks, Sabine and Stefan, for taking your time and energy to visit us! It was a pity, however, that your passage here was too brief to allow us further conversation in person…
[Sabine also reports on our brief meeting over at Backreaction].
Here is the preliminary program of the Philosophy of Gauge Theory workshop, to be held on Saturday-Sunday, 18-19 April 2009 at the Center for Philosophy of Science (University of Pittsburgh, USA):
The Abelian Higgs mechanism
Speaker: Ward Struyve
I have just received this message from the International Loop Quantum Gravity Seminar mailing list:
Valencia, March 26-28, 2009
The Workshop on Black Holes and Loop Quantum Gravity will take place in Valencia, Spain, from the 26th to the 28th of March, 2009. The purpose of the workshop is to bring together researchers working on quantum aspects of black holes, with emphasis on ideas that have originated in loop quantum gravity. A partial list of topics to be covered is as follows:
– Black hole entropy in LQG
– Spin foam approach to black holes
– Singularity resolution and information loss
– Prospects for a detailed description of the Hawking radiation
– Comparison between results from LQG and other approaches
This will be a ‘Discussion Workshop’. Therefore a significant time will be set aside for a critical evaluation of ideas that are being pursued in current research and on finding fertile directions for future work.
Title: Quantum field theory on a cosmological, quantum space-time
Authors: Abhay Ashtekar, Wojciech Kaminski, Jerzy Lewandowski
Title: Quantum Gravity on the Lattice
Authors: Herbert W. Hamber
Title: Quantum theory, noncommutative gravity, and the cosmological constant
Authors: T. P. Singh
Title: Singular sources in gravity and homotopy in the space of connections
Authors: E. Gravanis and S. Willison
This appears to be an interesting news coming from the ARCADE 2 experiment. I quote from their recent paper “Interpretation of the Extragalactic Radio Background”, M. Seiffert et al. 2008, ApJ, submitted (available here):
We have presented evidence for isotropic radio emission detected by ARCADE 2 beyond what can be explained by Galactic emission and the unresolved emission from the known population of discrete sources. The excess emission is consistent with a power law, with an index of −2.56, which is significantly flatter that what might be expected from an unidentified population of faint, diffuse, steep spectrum (index ∼ −2.7) radio sources associated with star-forming galaxies. We have also examined and placed limits on two classes of spectral distortions to the CMB. Such distortions are not supported by the data and cannot explain the excess emission (…)
We conclude that the three most important sources of error, Galactic emission, instrumental systematic errors, and radio emission from the faint end of the distribution of known sources, are unlikely to be sufficient to explain the excess emission presented here.
Two of the authors are Brazilian colleagues working at the Astrophysics Division at INPE (National Institute for Space Research, Brazil).
[Via Peter Woit]
For my record, I list here some interesting papers by Salisbury et al. which cover fundamental questions of relevance on, should I say, “pre-” quantum gravity matters.
The lines of research are summarized as follows:
- preservation of general coordinate transformation and additional gauge symmetries in the transition from a Lagrangian to a Hamiltonian description;
- the nature of observables in classical general relativity, and their potential usefulness in the construction of an eventual quantum theory of gravity;
- construction of diffeomorphism invariants (observables) in general relativity;
- history of constrained hamiltonians.
The papers of relevance are the following:
- Realization in phase space of general coordinate transformations [Phys. Rev. D 27, 740, 1983];
- Gauge transformations in the Lagrangian and Hamiltonian formalisms of generally covariant theories [gr-qc/9612037 = PRDvol55,no2,658,1997]: establishes the general framework in which gauge variables are retained as canonical variables;
- Reduced phase space: quotienting procedure for gauge theories [math-ph/9811029]: describes an alternative algorithm to the Dirac-Bergmann constraint procedure for constructing a self-consistent Hamiltonian model;
- Gauge group and reality conditions in Ashtekar’s complex formulation of canonical gravity [gr-qc/9912085]: discusses Ashtekar’s complex connection approach to gravity;
- Gauge Transformations in Einstein-Yang-Mills Theories [gr-qc/9912086]: discusses gauge symmetries in Einstein-Yang-Mills models;
- The gauge group in the real triad formulation of general relativity [gr-qc/9912087]: discusses a real triad version of canonical gravity;
- Gauge symmetries in Ashtekar’s formulation of general relativity [gr-qc/0004013]: proposes a gauge averaging procedure modeled after an approach of Rovelli’s, though retaining gauge variables and recognizing the essential distinction between time evolution and realizeable canonical gauge symmetries;
- Quantum general invariance and loop gravity [gr-qc/0105097]: preliminary exploration into the construction of diffeomorphism invariants using dynamical field-dependent finite gauge transformations;
- Quantum General Invariance [Proceedings of the Ninth Marcel Grossmann Meeting held in Rome in 2000 ("Quantum general invariance", in Proceedings of the Ninth Marcel Grossmann Meeting, edited by V.G. Gurzadyan, R. T. Jantzen and R. Ruffini, (World Scientific, New Jersey, 2002), 1300-1301)]: continued the exploration of finite gauge transformations;
- The issue of time in generally covariant theories and the Komar-Bergmann approach to observables in general relativity [ gr-qc/0503013 = Phys.Rev. D71 (2005) 124012]: constructs local invariants through the use of intrinsic coordinates. This can be accomplished in the canonical framework in general relativity using Weyl curvature scalars, as was first suggested by Komar and Bergmann. One essential new observation in this work is the recognition that gauge variables become functionals of the non-gauge variables, and consequently in the quantum theory they become subject to fluctuations. In particular, in canonical quantum gravity the light cone is itself fluctuating [the authors supposedly show that there is no conceptual problem for the canonical formulation of generally covariant theories because the mathematical identification of the Hamiltonian as a gauge generator is erroneous (resolution of the time evolution versus gauge problem)];
- Rosenfeld, Bergmann, Dirac and the Invention of Constrained Hamiltonian Dynamics [physics/0701299]: In a paper appearing in Annalen der Physik in 1930 Leon Rosenfeld invented the first procedure for producing Hamiltonian constraints. He displayed and correctly distinguished the vanishing Hamiltonian generator of time evolution, and the vanishing generator of gauge transformations for general relativity with Dirac electron and electrodynamic field sources. Though he did not do so, had he chosen one of his tetrad fields to be normal to his spacetime foliation, he would have anticipated by almost thirty years the general relativisitic Hamiltonian first published by Paul Dirac.
Links will be added later [Edit: almost all included now]. It would be interesting to follow these matters in light of recent advances in canonical quantum gravity. Marcus over at Physics Forums have prepared a selection (actually, an invitation to a poll) of papers published in the arxiv in 2008 in canonical quantum gravity.
I am looking for the scores of Bach’s Saint John’s Passion BWV 245, vocal and piano, in particular, the soprano cantata “Zerfließe, mein Herze, in Fluten der Zähren”. Up to now, my search was in vain.
Also, I need a good translation of the lyrics. For the moment, my german is very poor, I must admit. Here is what I managed to do:
Zerfließe, mein Herze, in Fluten der Zähren
Dem Höchsten zu Ehren!
Erzähle der Welt und dem Himmel die Not:
Dein Jesus ist tot!
Dissolve, my heart, in tides of the ???
to the highest one in honours!
Tell to the world and the sky the emergency:
Your Jesus is dead!
Is there a soul out there that could help me? My email is christinedantas [arroba] yahoo [ponto] com. I would be very much grateful…