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String theorists win Dirac Medal P-2 Is string theory a theory or a framework? What impacts will the Large Hadron Collider experiments have on the field? ICTP Dirac Medallists Juan Martín Maldacena, Joseph Polchinski and Cumrun Vafa share their insights on this proposal for a unified description of fundamental interactions in nature, and also describe what they find most exciting about string theory • • • ICTP celebrates Year of Darwin P-5 The link between physics and human evolution may not seem immediately obvious. Yet, the tools of modern physics can date human evolution and dispersal accurately. The tools and techniques used to pinpoint the age of human bones and teeth were the subject of an ICTP exhibit and lecture series held in conjunction with UNESCO’s symposium on Darwin, Evolution and Science • • • Focus on Africa CENTREFOLD ICTP has a long tradition of scientific capacity-building in Africa. Registrazione presso il Tribunale di Trieste n. 1044 del 01.03.2002 | Contiene Inserto Redazionale n. 1044 del 01.03.2002 | Contiene Inserto di Trieste il Tribunale presso Registrazione Over the last few decades, ICTP has supported numerous activities throughout the continent, including training programmes, networks and the establishment of affiliate centres. In Trieste, ICTP has welcomed more than 10,000 African visitors since 1970, providing advanced research and NEWSNEWS training opportunities unavailable to scientists in their home countries • • • NEW SCIENCE FOR CLEAN ENERGY (P-6) | EXPERIMENTAL PLASMA PHYSICS n°127 AT ICTP (P-7) | SNO DIRECTOR VISITS ICTP (P-8) | RESEARCH NEWS BRIEFS Spring/Summer 2009 (P-12) | NEW STAFF (P-16) | ACHIEVEMENTS/PRIZES (P-17) from ICTP Poste Italiane S.p.A. - Spedizione in Abbonamento Postale - D.L. 353/2003 (conv. in L. 27/02/2004 n° 46) art. 1, comma 2, DCB Trieste in L. 27/02/2004 n° 46) art. 1, comma - D.L. 353/2003 (conv. Postale S.p.A. - Spedizione in Abbonamento Italiane Poste NEWS from ICTP 127 + Cumrun Vafa received the Dirac Medal in June 2009, Noted physicists during the Summer School on Particle Physics in the LHC Era. ++ Juan Martín Maldacena and awarded Joseph Polchinski at the Dirac Medal 2008 award ceremony. Dirac Medals +++ Close-up of Dirac Medal. + ++ +++ are very primitive and more like a framework. Do you think string theory will ever be accepted as widely as the theory of general relativity? What would it take for that to happen? Maldacena: What is necessary is CEREMONY HONOURS WORK RELATED TO STRING THEORY that some prediction of the theory is experimentally verified. If that ICTP presented its Dirac Medal to the winners of the 2008 prize at a ceremony happens, it would then be accepted held on 26 March at the Centre. The Dirac Medal is given in honour of P.A.M. widely. Dirac, one of the greatest physicists of the 20th century and a staunch friend of ICTP, Polchinski: This question has two to scientists who have made significant parts: is it the right theory, and will DIRAC MEDALS contributions to physics. we know? For the first part, I feel The recipients—Juan Martín Maldacena strongly that it is the right theory. of the Institute for Advanced Study, More precisely, since it is incomplete, Princeton; Joseph Polchinski of the Kavli it is headed toward the right theory. Institute for Theoretical Physics, University of California at Santa Barbara; Part of the reason for this belief and Cumrun Vafa of Harvard University—were honoured for their substantial is theoretical: it ties together so contributions to string theory, a proposal for a unified description of many things that we already know. fundamental interactions in nature. For example, there is a theory of News from ICTP posed a number of questions related to string theory to the quantum gravity hidden in the three medallists; their thoughts on the theory are presented below. strong nuclear force, and this turns out to be string theory. Also, the Is string theory a theory or a framework? dark energy is an experimental hint, it was predicted by Steven Weinberg Maldacena: It is a theory under construction. We do not yet know what the based on assumptions that seem to fundamental principles underlying it are. follow from string theory. Will we ever know? In the long Polchinski: I think it is a theory because all signs are that its equations are term I am an optimist, one learns unique. But these equations have many solutions, so in a way it behaves as surprising things that were a framework. This property, having few equations with many solutions, is completely unexpected. essential to the nature of physics, which explains many phenomena in terms of a few principles. String theory is perhaps the extreme example of this. Vafa: Yes, I believe it will. It is hard to predict exactly how this will Vafa: It is in some aspects a theory and in others a framework. There are happen, but the richness of string pieces of string theory that are quite well developed, and there are parts which theory and the connections it already 3 has made with general relativity, in the next few years, but they seem true at LHC. We are fortunate to be quantum field theory and other areas to be a narrow class of possibilities. living in exciting times for particle of physics make this unavoidable. One possibility is that the string physics! scale is very low, of the order of the Are the Large Hadron Collider energies that will be explored at What is the most exciting aspect (LHC) experiments likely to have the LHC. The other is that cosmic of string theory for you? a fundamental impact on the field fundamental strings were produced of string theory? in the beginning of the big bang and Maldacena: It is the possibility of have survived until now. describing the initial instants of the Maldacena: Yes, discovering the It might be possible that big bang. We do not yet understand new layer of physics will probably be somebody understands the theory the theory well enough to say very useful for guiding us towards better and comes up with a whether it does indeed describe the correct theory. Understanding prediction that applies to a wider it, but this is the most exciting how electroweak symmetry is spectrum of possibilities. prospect and a strong motivation for broken is very important. Questions Finally, I should say that string developing the theory further. that will be answered are: Is there theory could be easily falsified by any a natural explanation for the scale experiment that shows a departure Polchinski: The way that it connects at which electroweak symmetry is from quantum mechanics. Since things. An example is the way that broken? Do we have supersymmetry string theory is based on quantum the strong nuclear force and gravity at this scale? mechanics, any violation of the usual are dual, just different classical rules of quantum mechanics by any limits of a single quantum theory. Polchinski: There are some possible tabletop experiment would rule out The duality between black holes smoking guns—extra dimensions string theory. and strongly interacting plasmas and black holes—but these are long is a striking illustration of this. shots. But whatever we learn will Polchinski: I have been studying Seemingly distant parts of physics be important, since there are so the possibility of cosmic strings, end up being closely related, in many possibilities now and a real which would have expanded with the surprising ways. mystery as to what will be seen. The universe and today might be seen strongest candidate, supersymmetry, through their gravitational effects. Vafa: The interconnection between is very interesting and is an Again, they are present in some ideas and the unifying framework important part of string theory, so if solutions but not all, so they are not a that string theory provides for the LHC has enough energy to find it firm prediction. But if they are found, physics is very exciting. Also, we are in good shape. they will be a huge new window into how one corner of string theory high-energy physics. transitions to another seamlessly Vafa: I believe it will, and I am through string dualities is quite hopeful that it would refine our Vafa: Together with my student beautiful. understanding of string theory. LHC Jonathan Heckman and with many is bound to have a lasting impact other collaborators, we have come How can fundamental science on the whole field of high-energy up with a framework from string contribute to the growth of physics. theory with very specific predictions developing countries? for particle physics and what LHC Can you give an example of a may find. This includes the mass of Maldacena: Researchers in basic prediction of string theory that supersymmetric particles we may areas of science are a resource for might be experimentally verified discover at LHC, as well as specific people who work on more applied in coming years? candidates for dark matter. We also areas, which would be the ones most have predictions for neutrino physics crucial for development. I do think Maldacena: We would have to be which would be interesting to verify that applied research is best done by lucky to have any verification in the in the near future experiments. I am the private sector, which has a better near future. There are scenarios hopeful that with some luck we may sense of what is most economically where verification would be possible see some of these predictions proven viable. NEWS from ICTP 127 Polchinski: I think that all people wonder about the nature of things, how they began and what is at the Dirac bottom of everything.
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