Fun_People Archive
14 Oct
PHYSICS NEWS UPDATE 452

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From: Peter Langston <psl>
Date: Thu, 14 Oct 99 12:38:48 -0700
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Subject: PHYSICS NEWS UPDATE 452
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	PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 452  October 12, 1999   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.  More information is available at
the Swedish Academy website:
http://www.nobel.se/announcement-99/physics99.html)

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 at http://www.nobel.se/announcement-99/chemistry99.html;
see also Scientific American, December 1990.)

© 1999 Peter Langston