Number 656, October 7, 2003
by Phillip F. Schewe, Ben Stein, and James Riordon
The 2003 Physics Nobel Prize
The 2003 Physics Nobel Prize goes to Alexei A. Abrikosov (Institute
for Physical Problems in Moscow and now at Argonne National Laboratory near Chicago),
Vitaly L. Ginzburg (Lebedev Physical Institute, Moscow) and Anthony J. Leggett (University of Illinois, Urbana).
The award goes for work done on systems that operate under two regimes
very far from human experience: the quantum realm and the low-temperature
realm. In superconductivity, a current of electrons flowing through
a material undergoes a change in behavior: normally reluctant to associate
with each other, the electrons at low temperature can form pairs. These
pairs act like particles and are so gregarious that they can enter into
a single unified quantum state.
In this state the electron pairs are no longer just a current, but
a "supercurrent." This supercurrent flows without dissipating
energy. It flows without resistance. The practical benefit is that energy
loss through dissipation can be eliminated. An additional feature is
that much higher currents can flow through some superconductor materials
than through normal metal wires. The price to pay for producing the
weird quantum state of superconductivity in the first place is having
to chill the material down to temperature close to absolute zero, which
usually means about 4 K.
Practical applications of wire made from superconducting material include
medical scanners (this year's Nobel for medicine rewards MRI research;
here potent magnetic fields inside the scanner are usually produced
with superconducting cables), levitated trains (still at an early state
of deployment), and the chilling of some components in cell-phone networks.
In some superconductors (type I) magnetic fields are anathema to the
superconducting state. In other superconductors (type II), magnetic
fields are tolerated, and this makes possible the applications just
mentioned. Abrikosov and Ginzburg are being recognized for their work in explaining how type II superconductors work. When a sample of
helium-3 atoms is chilled to very low temperature, the atoms (which like electrons in a superconductor, are "fermions,"
particles reluctant to associate) can pair up, and the pairs in turn
may enter into a single quantum state in which (analogous to the loss-less
flow of supercurrents in superconductors) the fluid will flow without
losing energy via friction.
Just as superconductors have no electrical resistance, so superfluids
have no viscosity, and can flow freely. Leggett is being recognized
for his work in explaining He-3 superfluidity. Superfluidity also appears
in samples of helium-4 atoms (although the superfluid mechanism is much
different than in He-3), and possibly in Bose Einstein condensates.
The 2003 Nobel Prize in Physiology/Medicine goes to Paul C. Lauterbur
of the University of Illinois at Urbana-Champaign and
Peter Mansfield of the University of Nottingham for their work in developing
magnetic resonance imaging, or MRI.
In the medical world, MRI has become a major imaging technique, but
its roots lie in the most basic magnetic physics in the nuclei at the
heart of every atom and molecule. Taking advantage of the fact that
the body is two-thirds water, MRI obtains images of the hydrogen nuclei
in water molecules inside our bodies.
In the early 1970s, while working at the State University of New York
at Stony Brook, Lauterbur exploited the magnetic properties of atomic
nuclei to yield a two-dimensional image of matter, by introducing gradients
in the external magnetic field that surrounds the object to be imaged.
Shortly thereafter, Peter Mansfield helped to make MRI a practical imaging
procedure, in part by coming up with mathematical methods for processing
the radio waves released by hydrogen during the technique.
The origins of MRI go back further, to the late 1930s, when physicist
I.I. Rabi of Columbia University demonstrated that one could obtaining
abundant information about lithium chloride molecules by manipulating
the magnetic "spins" of the molecules' nuclei (Nobel Prize,
1944). Later, physicists E.M. Purcell (Harvard) and Felix Bloch (Stanford)
developed nuclear magnetic resonance (NMR) in hydrogen (Nobel Prize,
1952). Two Nobel Prizes in Chemistry (1991 and 2002) have been awarded
for achievements in nuclear magnetic resonance.
MRI has been so successful that the original technique has spawned numerous
offshoots, such as functional MRI (fMRI), which measures brain activity
by detecting oxygen levels in specific brain areas. MRI advances continue
at a feverish pace: low-field MRI (Some background articles: Physics
Today, Jun 1995, Sep 2001, Jun 92, Oct 2003; Scientific American, May
82, Oct 2001, Jan 83)
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