TIME: Almanac 1993/TIME Almanac 1993.iso/time/041690/0416300.000

Text File | 1992-08-28 | 5.8 KB | 123 lines

                ÄåΣ#                                                          SCIENCE, Page 57

Can We Really Understand Matter?


By EUGENE LINDEN


    Few tasks are more daunting than standing in the path of a
charging theoretical physicist who is hell-bent on getting
funding for the next particle accelerator. As practitioners of
the hardest of the hard sciences, physicists do little to
discourage their aura of intellectual supremacy, particularly
when suggesting to Congress that a grand synthesis of all the
forces of nature is at hand if the Government will only cough
up a few billion dollars more. But what if this confidence is
misplaced? What if the barriers to knowledge are higher than
many physicists like to admit?

    For much of this century, scientists have known that the
comfortable solidity of things begins to break down at the
subatomic level. Like the Hindu veil of Maya, the palette from
which nature paints atoms proves illusory when approached. From
afar, this world appears neatly separated into waves and
particles, but close scrutiny reveals indescribable objects
that have characteristics of both.

    Physicists have prospered in this quirky realm, but neither
physics nor the rest of science has fully digested its
implications. Inside the atom is a world of perpetual
uncertainty in which particle behavior can be expressed only
as a set of probabilities, and reality exists only in the eyes
of the observer. Though the recognition of this uncertainty
grew in part out of Albert Einstein's work, the idea bothered
him immensely. "God does not play dice with the universe," he
remarked.

    The set of mathematical tools developed to explore the
subatomic world is called quantum mechanics. The theory works
amazingly well in predicting the behavior of quarks, leptons
and the like, but it defies common sense, and its equations
imply the existence of phenomena that seem impossible. For
instance, under special circumstances, quantum theory predicts
that a change in an object in one place can instantly produce
a change in a related object somewhere else -- even on the
other side of the universe.

    Over the years, this seeming paradox has been stated in
various ways, but its most familiar form involves the behavior
of photons, the basic units of light. When two photons are
emitted by a particular light source and given a certain
polarization (which can be thought of as a type of
orientation), quantum theory holds that the two photons will
always share that orientation. But what if an observer altered
the polarization of one photon once it was in flight? In
theory, that event would also instantaneously change the
polarization of the other photon, even if it was light-years
away. The very idea violates ordinary logic and strains the
traditional laws of physics.

    The two-photon puzzle was nothing more than a matter of
speculation until 1964, when an Irish theoretical physicist
named John Stewart Bell restated the problem as a simple
mathematical proposition. A young physicist named John Clauser
came upon Bell's theorem and realized that it opened the door
to testing the two-photon problem in an experiment. Like
Einstein, Clauser was bothered by the seemingly absurd
implications of quantum mechanics. Says Clauser, now a research
physicist at the University of California, Berkeley: "I had an
opportunity to devise a test and see whether nature would
choose quantum mechanics or reality as we know it." In his
experiment, Clauser, assisted by Stuart Freedman, found a way
of firing photons in opposite directions and selectively
changing their polarization.

    The outcome was clear: a change in one photon did alter the
polarization of the other. In other words, nature chose quantum
mechanics, showing that the two related photons could not be
considered separate objects, but rather remained connected in
some mysterious way. This experiment, argues physicist Henry
Stapp of Lawrence Berkeley Laboratories, imposes new limits on
what can be established about the nature of matter by proving
that experiments can be influenced by events elsewhere in the
universe.

    Clauser's work pointed out once again that the rules of
quantum mechanics do not mesh well with the laws of Newton and
Einstein. But most physicists do not see the apparent disparity
to be a major practical problem. Classical laws work perfectly
well in explaining phenomena in the visible world -- the motion
of a planet or the trajectory of a curveball -- and quantum
theory does just as well when restricted to describing
subatomic events like the flight of an electron.

    Yet a small band of physicists, including Clauser and Stapp,
are disturbed by their profession's priorities, believing that
the anomalies of quantum theory deserve much more
investigation. Instead of chasing ever smaller particles with
ever larger accelerators, some of these critics assert, physics
should be moving in the opposite direction. Specifically,
science needs to find out whether the elusiveness of the
quantum world applies to objects larger than subatomic
particles.

    No one worries about the relevance of quantum mechanics to
the momentum of a charging elephant. But there are events on
the border between the visible and the invisible in which
quantum effects could conceivably come into play. Possible
examples: biochemical reactions and the firing of neurons in
the brain. Stapp, Clauser and others believe that a better
understanding of how quantum theory applies to atoms and
molecules might help in everything from artificial-intelligence
research to building improved gyroscopes. For now, though,
this boundary area is a theoretical no-man's-land. Certainly
physicists are a lot further from understanding how the world
works than some would have Congress believe.