12 OCTOBER 1999
THE NOBEL PRIZE IN PHYSICS 1999
Background in English by Professor Cecilia Jalskog (PDF-file)The Royal Swedish Academy of Sciences has awarded the 1999 Nobel Prize in Physics jointly to ProfessorGerardus 't Hooft, University of Utrecht, Utrecht, the Netherlands, and Professor EmeritusMartinus J.G. Veltman, Bilthoven, the Netherlands.
The two researchers are being awarded the Nobel Prize for having placed particle physics theory on a firmer mathematical foundation. They have in particular shown how the theory may be used for precise calculations of physical quantities. Experiments at accelerator laboratories in Europe and the USA have recently confirmed many of the calculated results.
The Academy's citation:
"for elucidating the quantum structure of electroweak interactions in physics."
Further reading
- In search of the Ultimate Building Blocks by Gerard 't Hooft, Cambridge University Press 1997.
- The Higgs boson by Martinus J.G. Veltman, Scientific American, November 1986, p.88.
- An Elementary Primer for Gauge Theory by K. Moriyasu, World Scientific Publishing 1983.
- Gauge Theories of the Forces between Elementary Particles by Gerard 't Hooft, Scientific American, June 1980, p. 90.
The laureates:
Gerardus 't Hooftborn 1946 in Den Helder, the Netherlands. Dutch citizen. Doctoral degree in physics 1972 at University of Utrecht. Professor of Physics at University of Utrecht since 1977. Among other awards 't Hooft received the 1979 Dannie Heineman Prize from the American Physical Society and the 1982 Wolf Prize for his work on renormalizing gauge theories. Member of the Dutch Academy of Sciences since 1982.
Martinus J.G.Veltman
born 1931 in the Netherlands. Dutch citizen. Doctoral degree in physics 1963 at University of Utrecht. Professor of Physics at University of Utrecht 1966-1981 and at University of Michigan, Ann Arbor, from 1981 (now retired). Among other awards Veltman received the 1993 High Energy and Particle Physics Prize from the European Physical Society for his work on renormalizing gauge theories. Member of the Dutch Academy of Sciences since 1981.
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics NewsNumber 452 October 12, 1999by Phillip F. Schewe and Ben Stein
THE 1999 NOBEL PRIZE FOR PHYSICS goes to Gerardus 'tHooft of the University of Utrecht and Martinus Veltman, formerlyof the University of Michigan and now retired, for their worktoward deriving a unified framework for all the physical forces.Their efforts, part of a tradition going back to the nineteenthcentury, centers around the search for underlying similarities orsymmetries among disparate phenomena, and the formulation ofthese relations in a complex but elegant mathematical language. Apast example would be James Clerk Maxwell's demonstration thatelectricity and magnetism are two aspects of a single electro-magnetic force.
Naturally this unification enterprise has met with variousobstacles along the way. In this century quantum mechanics wascombined with special relativity, resulting in quantum field theory.This theory successfully explained many phenomena, such as howparticles could be created or annihilated or how unstable particlesdecay, but it also seemed to predict, nonsensically, that thelikelihood for certain interactions could be infinitely large. Richard Feynman, along with Julian Schwinger and Sin-ItiroTomonaga, tamed these infinities by redefining the mass and chargeof the electron in a process called renormalization. Their theory,quantum electrodynamics (QED), is the most precise theory known,and it serves as a prototype for other gauge theories (theories whichshow how forces arise from underlying symmetries), such as theelectroweak theory, which assimilates the electromagnetic and weaknuclear forces into a single model.
But the electroweak model too was vulnerable to infinities andphysicists were worried that the theory would be useless. Then 'tHooft and Veltman overcame the difficulty (and the anxiety)through a renormalization comparable to Feynman's. To draw outthe distinctiveness of Veltman's and 't Hooft's work further, onecan say that they succeeded in renormalizing a non-Abelian gaugetheory, whereas Feynman had renormalized an Abelian gauge theory(quantum electrodynamics). What does this mean? A mathematicalfunction (such as the quantum field representing a particle'swhereabouts) is invariant under a transformation (such as a shift inthe phase of the field) if it remains the same after the transformation.One can consider the effect of two such transformations, A and B.An Abelian theory is one in which the effect of applying A and thenB is the same as applying B first and then A. A non-Abelian theoryis one in which the order for applying A and B does make adifference. Getting the non-Abelian electroweak model to work wasa formidable theoretical problem.
An essential ingredient in this scheme was the existence ofanother particle, the Higgs boson (named for Peter Higgs), whoserole (in a behind-the-scenes capacity) is to confer mass upon manyof the known particles. For example, interactions between the Higgsboson and the various force-carrying particles result in the W and Zbosons (carriers of the weak force) being massive (with masses of80 and 91 GeV, respectively) but the photon (carrier of theelectromagnetic force) remaining massless.
With Veltman's and 't Hooft's theoretical machinery in hand,physicists could more reliably estimate the masses of the W and Z,as well as produce at least a crude guide as to the likely mass of thetop quark. (Mass estimates for exotic particles are of billion-dollarimportance if Congress, say, is trying to decide whether or not tobuild an accelerator designed to discover that particle.) Happily,the W, Z, and top quark were subsequently created and detected inhigh energy collision experiments, and the Higgs boson is now itselfan important quarry at places like Fermilab's Tevatron and CERN'sLarge Hadron Collider, under construction in Geneva.
(Recommended reading: 't Hooft, Scientific American, June1980, excellent article on gauge theories in general; Veltman,Scientific American, November 1986, Higgs bosons.
THE 1999 NOBEL PRIZE IN CHEMISTRY goes to Ahmed H.Zewail of Caltech, for developing a technique that enables scientiststo watch the extremely rapid middle stages of a chemical reaction.Relying on ultra-fast laser pulses, "femtosecond spectroscopy" canprovide snapshots far faster than any camera--it can capture themotions of atoms within molecules in the time scale offemtoseconds (10^-15 s).
An atom in a molecule typically performs a single vibration injust 10-100 femtoseconds, so this technique is fast enough to discerneach and every step of any known chemical reaction. Shining pairsof femtosecond laser pulses on molecules (the first to initiate areaction and the second to probe it) and studying what type of lightthey absorb yields information on the atoms' positions within themolecules at every step of a chemical reaction. With this technique,Zewail and his colleagues first studied (in the late 1980s) a 200-femtosecond disintegration of iodocyanide (ICN-->I+CN),observing the precise moment at which a chemical bond betweeniodine and carbon was about to break.
Since then, femtochemistry has revealed a whole new class ofintermediate chemical compounds that exist less than a trillionth of asecond between the beginning and end of a reaction. It has alsoprovided a way for controlling the courses of chemical reaction anddeveloping desirable new materials for electronics. It has providedinsights on the dissolving of liquids, corrosion and catalysis onsurfaces (see Physics Today, October 1999, p. 19); and themolecular-level details of how chlorophyll molecules can efficientlyconvert sunlight into useable energy for plants during the process ofphotosynthesis. (Official announcement and further info here; see alsoScientific American, December 1990.)
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