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Qubits encoded in time advance the prospects for quantum computing with single photons. Published Wed Oct 09, 2013
Qubits encoded in time advance the prospects for quantum computing with single photons. Published Wed Oct 09, 2013
about 2 hours ago
Gravity waves. They are pretty but have nothing to do with gravitational waves. Image Source: UWO.Krauss and Wilczek recently posted a brief note on the arXiv. They present a dimensional argument that claims signatures of relic gravitati...
Gravity waves. They are pretty but have nothing to do with gravitational waves. Image Source: UWO.Krauss and Wilczek recently posted a brief note on the arXiv. They present a dimensional argument that claims signatures of relic gravitational waves in the cosmic microwave background (CMB) would be evidence for quantum gravity. Using Cosmology to Establish the Quantization of GravityLawrence M. Krauss, Frank WilczekarXiv:1309.5343 [hep-th]Relic gravitational waves are perturbations of space-time created at the Big Bang. They cannot presently be directly detected, but if they exist they would affect the polarization of CMB photons. The Planck satellite mission is about to deliver data on CMB polarization, so Krauss and Wilczek’s is a very timely contribution. While their dimensional argument is original and compelling in its simplicity, what they say is not particularly surprising and known to researchers familiar with the subject. The argument means essentially if there are no suitable matter sources that could cause space-time perturbations, then the only way relic gravitational waves can have been created is through quantum effects. That’s because it needs a mass scale to get the dimensions right and Newton’s constant will only give a mass-scale when suitably combined with Planck’s constant, thus indicating a quantum effect. The argument however only works without matter that brings in anisotropic stress. It would still work if the matter was solely scalar fields because these don’t contribute to the anisotropic stress, but electromagnetic radiation could deliver such a contribution. Be that as it may, this means by a purely dimensional argument alone it is hard if not impossible to reverse the logical arrow, that being the question whether relic gravitational waves could have been created in a non-quantum fashion. Few few people doubt that relic gravitational waves exist and are quantized. It would certainly be exciting to have evidence that this treatment of the early universe is correct, but it must be said that this is not evidence for what the community commonly refers to as quantum gravity. “Quantum gravity” is normally meant to be the fundamental theory for the quantum nature of space and time. The quantization that is being used for gravity in the early universe is normally explicitly referred to as “perturbatively quantized gravity”. It is expected by all but a few dissidents that perturbatively quantized gravity is the correct effective limit of any theory of quantum gravity. The mere existence of such quantized perturbations thus tells us little. More telling is the spectrum of the perturbations which depends on what happened in the early universe, for example on whether there was a Big Bang or a Big Bounce, and that does indeed depend on the full theory of quantum gravity.Evidence for relic gravitational waves would give strong support to the validity of perturbatively quantized gravitational waves (essentially quantum field theory in curved background), but it takes more than a dimensional argument to show that other models cannot produce the same observation. And even if that could be shown, the mere existence of the gravitational wave background does not teach us much about the non-perturbative theory of quantum gravity. Thus, Krauss and Wilczek’s argument makes a good point but its relevance for research in quantum gravity is limited.Kudos to Jakub Mielczarek for helpful communication.Bonus: Krauss at a recent discussion following his public lecture in Stockholm. Spot the American among the Swedes :p Lawrence Krauss in Stockholm. Still from this YouTube Video.
about 12 hours ago
Ian Marquette and Christiane Quesne New ladder operators are constructed for a rational extension of the harmonic oscillator associated with type III Hermite exceptional orthogonal polynomials and characterized by an even integer m. The...
Ian Marquette and Christiane Quesne New ladder operators are constructed for a rational extension of the harmonic oscillator associated with type III Hermite exceptional orthogonal polynomials and characterized by an even integer m. The eigenstates of the Hamiltonian separate into m + 1 infinite-dimensional unitary irreducible represe ... [J. Math. Phys. 54, 102102 (2013)] published Tue Oct 8, 2013.
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1 day ago
M. A. Rego-Monteiro and F. D. Nobre An exact classical field theory for nonlinear quantum equations is presented herein. It has been applied recently to a nonlinear Schrodinger equation, and it is shown herein to hold also for a nonline...
M. A. Rego-Monteiro and F. D. Nobre An exact classical field theory for nonlinear quantum equations is presented herein. It has been applied recently to a nonlinear Schrodinger equation, and it is shown herein to hold also for a nonlinear generalization of the Klein-Gordon equation. These generalizations were carried by introducing no ... [J. Math. Phys. 54, 103302 (2013)] published Tue Oct 8, 2013.
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Jian Zhang, Xianhua Tang, and Wen Zhang This paper is concerned with the following nonperiodic Dirac equation i[summation]alpha[partial-derivative]u+abetau+M(x)u=F(x,u) in [openface R], where M(x) is a vector potential. Under weak super...
Jian Zhang, Xianhua Tang, and Wen Zhang This paper is concerned with the following nonperiodic Dirac equation i[summation]alpha[partial-derivative]u+abetau+M(x)u=F(x,u) in [openface R], where M(x) is a vector potential. Under weak superquadratic condition on the nonlinearity, we establish the existence of ground state solutions of Nehari ... [J. Math. Phys. 54, 101502 (2013)] published Tue Oct 8, 2013.
1 day ago
Congratulations to Francois Englert and Peter Higgs, awarded the 2013 physics Nobel prize this morning. Evidently the prize announcement was delayed because they were unable to reach Higgs by phone. Surely he wasn’t unaware that t...
Congratulations to Francois Englert and Peter Higgs, awarded the 2013 physics Nobel prize this morning. Evidently the prize announcement was delayed because they were unable to reach Higgs by phone. Surely he wasn’t unaware that today was a day he might be getting an early morning phone call… The Higgs discovery last year was one of the great milestones of fundamental physics research and it would have been very odd for the Nobel committee to not recognize it with a prize this year. I do think though that the way they chose to do this is not ideal, for a couple reasons. The first is that this was foremost an experimental achievement, but the experimentalists and their work remains unrecognized. The thousands of physicists and engineers of CERN, LHC and ATLAS have accomplished something amazing by working together, but this makes them somehow ineligible for the Nobel. As far as the Nobel goes they make the mistake of running their collaborations relatively democratically, without a “great man” (or “great woman”) who could stand out and be awarded a prize. Another issue with today’s choice is that if you do want to emphasize a model of scientific research where advances come from a specific “great man” theorist, in this case they’ve left out the greatest one involved. The specific model tested at the LHC was not that of Englert and Higgs, but the one that Weinberg and Salam already got a prize for. The new prize is for the general mechanism, but this is something that was first understood by Philip Anderson a couple years before Englert and Higgs. For some details of the history, see here. The argument is often made that Anderson’s model was not relativistic, but this is a phenomenon for which relativity is not relevant, something which Anderson understood. The Nobel prize announcement comes with a detailed discussion of the history, which discusses extensively Anderson’s work. It makes the argument that relativity was a crucial issue, and summarizes the situation with: This was a very important step forward showing that one could indeed have massive vector particles without having a massless model, but it did now show how the same phenomenon would work in a relativistically invariant theory. Anderson concluded by saying “We conclude then, that the Goldstone zero-mass difficulty is not a serious one, because we can probably cancel it off against an equal Yang-Mills zero-mass problem.” Weirdly, this paragraphs contains a crucial typo. I assume they meant to write “it did not show” instead of “it did now show”. The authors refer to what is usually called the “Higgs mechanism” as the “BEH Mechanism”, but it seems to me that if you want to insist on adding more names to the usual terminology, “Anderson-Higgs” would be better. As far as the Nobel goes, Anderson already has one, given for other work, and maybe this is one reason he was left out this time (although getting multiple Nobel prizes is not unprecedented). Congratulations to him and the LHC experimentalists today, as well as to Englert and Higgs. Update: Jon Butterworth has some similar comments at the Guardian, especially about the “lone genius” model for progress in science. Update: For more from Anderson about his work on this topic, see interviews by Chandra, Coleman and Sondhi at the AIP oral history site here. One of the things I find most surprising about this history is that Brout was in close contact with Anderson during this period, but does not refer to Anderson’s 1963 paper in the original Brout-Englert paper, or in later discussions of the history (see here). Here’s Anderson’s account: during this period I was in fairly close contact with Bob Brout. Later on, one of the co-inventors of the Higgs mechanism is Brout with Francois Englert. Bob spent several summers with us down
1 day ago
Englert and Higgs take it! In other news, water still wet, sky still blue. Just kidding, it could have gone to all sorts of other deserving people. Still, I don't think anyone was surprised. Peter Higgs doesn't know yet, though. Th...
Englert and Higgs take it! In other news, water still wet, sky still blue. Just kidding, it could have gone to all sorts of other deserving people. Still, I don't think anyone was surprised. Peter Higgs doesn't know yet, though. The Nobel Prize Committee tried to call, but Higgs didn't pick up. If you see him, please let him know. If you want a little more, you can read the APS press release about the 2013 Nobel Prize for Physics.
1 day ago
Pair honoured for their prediction of the Higgs boson
Pair honoured for their prediction of the Higgs boson
1 day ago
Later today (or tomorrow depending on where you are based), the winner(s) of the Nobel Prize for Physics will be announced. At the time that I am writing this, the hot favorites are some combination of the theoretical physicists who pred...
Later today (or tomorrow depending on where you are based), the winner(s) of the Nobel Prize for Physics will be announced. At the time that I am writing this, the hot favorites are some combination of the theoretical physicists who predicted the Higgs mechanism. (Gerry Guralnik blogs for us about his role in the prediction.) Many are also calling for the ATLAS and CMS collaborations to be recognized for the discovery of the Higgs boson at the Large Hadron Collider (LHC), the underground accelerator that is so vast it crosses the border between Switzerland and France.This brings to mind a question posed by artist Lyndall Phelps, whom I met a few weeks ago at the launch of her particle-physics inspired exhibition, Covariance, open now at the London Canal Museum. Phelps pondered what our descendants would make of these huge subterranean structures, if they stumbled onto them during an archeological dig. Whether or not they would fathom the purpose of such detectors, they will surely be struck by their beauty. On one of my visits to the LHC, CERN's research director, Sergio Bertolucci urged me to visit the underground heart of the accelerator before the detectors were finally closed off for data-taking, describing the experience of first encountering the machinery as "magnificent, like standing within a cathedral." Bertolucci's promise was more than fulfilled when I saw the detectors. So I would not have envied Phelps the task she was appointed some months ago by the UK's Institute of Physics: to create a piece of art that evokes the majesty of such large-scale particle physics experiments. In collaboration with Ben Still, a particle physicist at Queen Mary, University of London (and an FQXi blogger and frequent podcast contributor), Phelps designed and built the Covariance installation (image, top right). The artwork is inspired by the Superkamiokande neutrino observatory in Japan, where Still works. It is a huge and impressive piece, made up of 1 km of brass rods, 28,000 glass beads, hundreds of acrylic discs and 36,000 diamantes. The installation is suspended in the circular brick space--about 30 feet in diameter--of a Victorian ice well. I spoke with both Phelps and Still for this month's podcast. You can hear them discuss the themes that they hoped to bring out with the piece. The most obvious note that strikes you when you first see it is the rotational symmetry that mimics the structure of particle physics detectors (Superkamiokande image, right), a...
1 day ago
First a sad piece of news, via commenter Bob Jones. It seems that David Kazhdan, a well-known representation theorist, was hit by a truck Saturday morning while bicycling in Jerusalem. He’s in the hospital, with his condition desc...
First a sad piece of news, via commenter Bob Jones. It seems that David Kazhdan, a well-known representation theorist, was hit by a truck Saturday morning while bicycling in Jerusalem. He’s in the hospital, with his condition described as “very serious”. I hope he manages to recover soon from this accident. On a much happier note, I spent Saturday at the Simons Foundation attending a day-long program celebrating the work of Pierre Deligne. More technical talks were in the morning, with Goncharov giving a talk on this material, and Illusie discussing the mathematical significance of several letters he had received from Deligne. Deligne’s contributions to mathematics are immense, and go way beyond his many published works. Quite a few mathematicians have received letters like the ones Illusie discussed, laying out all sorts of new ideas. Some of these ended up getting worked out in detail by students and others, with Deligne’s name not necessarily attached. To this day, Deligne continues to send highly helpful hand-written letters about mathematics to people, although I understand that these days they arrive not by snail mail, but as a scan sent by e-mail by a secretary. These letters make up a huge resource for mathematics, perhaps someday a way will be found to archive them and make them more widely available. In the afternoon, Brian Conrad and Ravi Vakil gave some very good more general talks, with one theme the Weil conjectures that Deligne was responsible for finishing the proof of. The day ended with reminiscences of Deligne from Illusie, Saint-Donat, and Dennis Sullivan (since Sullivan couldn’t be there, his contribution was read off a cell-phone by Jim Simons). Contemplating Deligne’s remarkable career is rather awe-inspiring. For more about him, a good place to start is this page at the Simons Foundation, which includes videos of an interview of Deligne by Robert MacPherson. See also this recent piece by Illusie, which makes the point that one of Deligne’s achievements was to bring together two great but disparate currents in mathematics, the abstract algebraic geometers around Grothendieck, and the representation theorists working on what is now called the Langlands program. For yet more unification of mathematics and physics, last week the Mathematical Institute at Oxford hosted a conference on Number Theory and Physics, associated with talks celebrating the Institute’s new building (see here and here). Witten’s slides are available here and here, a blog posting by Bruce Bartlett is here. Via Jordan Ellenberg and Mathbabe, there’s the news that Andrew Wiles took the occasion of the building opening ceremony to warn about the abuse of mathematics by the financial industry. By the way, the new building is described as housing 500 mathematicians and staff, which seems to me truly huge, quite a bit bigger than any other math institute I know of. A journalist at Science magazine got not just one, but 157 open access science journals to accept a bogus completely incompetent paper. One could take this as conclusive evidence for the problem with open access journals, except that he didn’t try this also on conventional journals, and many believe that they too would publish something just as bad. Brian Leiter has a discussion here of some data here about the fraction of philosophy Ph.Ds that are able to get tenure-track jobs. I had always thought that academic philosophy Ph.D.s were likely to have even worse job prospects than theoretical physicists. If you believe these numbers at all though, your job prospects as a philospher are dramatically better than similar numbers for physics theory Ph.D.s. My guess is that, at least in the US, theoretical physics Ph.D.s have very roughly a 20% chance of finding a permanent academic position, while the data here shows 60% of similar philosophy Ph.D.s with permanent positions. If you’re in a
2 days ago