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2Physics Quote:
"Can photons in vacuum interact? The answer is not, since the vacuum is a linear medium where electromagnetic excitations and waves simply sum up, crossing themselves with no interaction. There exist a plenty of nonlinear media where the propagation features depend on the concentration of the waves or particles themselves. For example travelling photons in a nonlinear optical medium modify their structures during the propagation, attracting or repelling each other depending on the focusing or defocusing properties of the medium, and giving rise to self-sustained preserving profiles such as space and time solitons or rapidly rising fronts such as shock waves." -- Lorenzo Dominici, Mikhail Petrov, Michal Matuszewski, Dario Ballarini, Milena De Giorgi, David Colas, Emiliano Cancellieri, Blanca Silva Fernández, Alberto Bramati, Giuseppe Gigli, Alexei Kavokin, Fabrice Laussy, Daniele Sanvitto. (Read Full Article: "The Real-Space Collapse of a Two Dimensional Polariton Gas" )

Wednesday, March 07, 2007

High Energy Physics: 5 Needed Breakthroughs
-- Barry Barish

[Our today's guest in the ongoing feature '5 Breakthroughs' is Prof. Barry Barish (photo courtesy: Caltech).

Barry Barish is a Linde Professor of Physics, Emeritus at the California Institute of Technology, where he taught and conducted research since 1963. He is also the Director of the Global Design Effort for the International Linear Collider.

One of Prof. Barish's noteworthy experiments was at Fermilab using high energy neutrinos to reveal the quark substructure of the nucleon. These experiments were among the first to observe the weak neutral current, a linchpin in the Eletro-Weak unification theory of Glasgow, Salam and Weinberg.

In 1980s Prof. Barish led an international effort to build a sophisticated underground detector (MACRO) in Italy to search for magnetic monopole and solve other related problems in the emerging field of particle astrophysics. The experiment provided the best limits for the Grand Unified magnetic monopoles and some of the key evidences that neutrinos have mass.

In 1994, Prof. Barish became Principal Investigator of the joint Caltech-MIT LIGO project for the detection of gravitational waves and later became Director of the Laboratory from 1997 to 2005.

In 2002 he was nominated to the National Science Board that helps oversee the National Science Foundation (NSF) and advises the President and Congress on policy issues related to science, engineering and education. In 2002 he received the Klopsteg award of the American Association of Physics Teachers (AAPT) and was elected to the National Academy of Sciences. In 2003, he served as a member of the special panel for NASA that considered the future of the Hubble Space Telescope and the transition to the James Webb Space Telescope. Prof. Barish also served as co-chair of the subpanel of the High Energy Physics Advisory Panel (HEPAP) that developed the long-range plan for high energy physics in USA.

Here is Prof. Barish's list of 5 breakthroughs that he would like to see in high energy physics.
-- 2Physics.com Team]

"5 most important breakthroughs that are needed for particle physics:

1) Understanding what is the dark energy in the universe? (We don't even have a good idea here)

2) What is the dark matter? (This is the other big unknown, but at least we have some handles. We know it is non-baryonic and evidence points to either supersymmetric particles, or maybe axions. Perhaps it is neither)

3) What causes mass? (We have a very successful theory of particle physics, but the particles are massless. We need to understand the source of mass. The leading idea is that it is the Higgs mechanism, and we need to see if there is a Higgs particle or variant to make the next step. The Large Hadron Collider at CERN should answer this question)

4) Is the neutrino its own antiparticle? (This is a puzzle going back to Fermi and perhaps the next generation of experiments will resolve it by looking for neutrino-less double beta decay)

5) Is there ultimate unification of the forces of nature? (This is a long term intriguing simplification on our understanding of particles and fields, but present data does not support it. However, if there is a new symmetry in nature (supersymmetry) it could bring this unification.

These are all questions and there is hope we will have much better understanding within a decade or two."

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