Carl Koppeschaar

www.kva.se

12 OCTOBER 1999

THE NOBEL PRIZE IN PHYSICS 1999

The Royal Swedish Academy of Sciences has awarded the 1999 Nobel Prize in Physics jointly to Professor Gerardus 't Hooft, University of Utrecht, Utrecht, the Netherlands, and Professor Emeritus Martinus 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."

Full story here.

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:

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

by Phillip F. Schewe and Ben Stein

THE 1999 NOBEL PRIZE FOR PHYSICS goes to Gerardus 't Hooft of the University of Utrecht and Martinus Veltman, formerly of the University of Michigan and now retired, for their work toward deriving a unified framework for all the physical forces. Their efforts, part of a tradition going back to the nineteenth century, centers around the search for underlying similarities or symmetries among disparate phenomena, and the formulation of these relations in a complex but elegant mathematical language. A past example would be James Clerk Maxwell's demonstration that electricity and magnetism are two aspects of a single electro- magnetic force.

Naturally this unification enterprise has met with various obstacles along the way. In this century quantum mechanics was combined with special relativity, resulting in quantum field theory. This theory successfully explained many phenomena, such as how particles could be created or annihilated or how unstable particles decay, but it also seemed to predict, nonsensically, that the likelihood for certain interactions could be infinitely large. Richard Feynman, along with Julian Schwinger and Sin-Itiro Tomonaga, tamed these infinities by redefining the mass and charge of 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 which show how forces arise from underlying symmetries), such as the electroweak theory, which assimilates the electromagnetic and weak nuclear forces into a single model.

But the electroweak model too was vulnerable to infinities and physicists were worried that the theory would be useless. Then 't Hooft and Veltman overcame the difficulty (and the anxiety) through a renormalization comparable to Feynman's. To draw out the distinctiveness of Veltman's and 't Hooft's work further, one can say that they succeeded in renormalizing a non-Abelian gauge theory, whereas Feynman had renormalized an Abelian gauge theory (quantum electrodynamics). What does this mean? A mathematical function (such as the quantum field representing a particle's whereabouts) is invariant under a transformation (such as a shift in the 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 then B is the same as applying B first and then A. A non-Abelian theory is one in which the order for applying A and B does make a difference. Getting the non-Abelian electroweak model to work was a formidable theoretical problem.

An essential ingredient in this scheme was the existence of another particle, the Higgs boson (named for Peter Higgs), whose role (in a behind-the-scenes capacity) is to confer mass upon many of the known particles. For example, interactions between the Higgs boson and the various force-carrying particles result in the W and Z bosons (carriers of the weak force) being massive (with masses of 80 and 91 GeV, respectively) but the photon (carrier of the electromagnetic 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 the top quark. (Mass estimates for exotic particles are of billion-dollar importance if Congress, say, is trying to decide whether or not to build an accelerator designed to discover that particle.) Happily, the W, Z, and top quark were subsequently created and detected in high energy collision experiments, and the Higgs boson is now itself an important quarry at places like Fermilab's Tevatron and CERN's Large Hadron Collider, under construction in Geneva.

(Recommended reading: 't Hooft, Scientific American, June 1980, 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 scientists to watch the extremely rapid middle stages of a chemical reaction. Relying on ultra-fast laser pulses, "femtosecond spectroscopy" can provide snapshots far faster than any camera--it can capture the motions of atoms within molecules in the time scale of femtoseconds (10^-15 s).

An atom in a molecule typically performs a single vibration in just 10-100 femtoseconds, so this technique is fast enough to discern each and every step of any known chemical reaction. Shining pairs of femtosecond laser pulses on molecules (the first to initiate a reaction and the second to probe it) and studying what type of light they absorb yields information on the atoms' positions within the molecules 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 between iodine and carbon was about to break.

Since then, femtochemistry has revealed a whole new class of intermediate chemical compounds that exist less than a trillionth of a second between the beginning and end of a reaction. It has also provided a way for controlling the courses of chemical reaction and developing desirable new materials for electronics. It has provided insights on the dissolving of liquids, corrosion and catalysis on surfaces (see Physics Today, October 1999, p. 19); and the molecular-level details of how chlorophyll molecules can efficiently convert sunlight into useable energy for plants during the process of photosynthesis. (Official announcement and further info here; see also Scientific American, December 1990.)

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