SCIENCE'S great gift to human understanding of the material world can be
epitomized in a single word — simplicity. When applied to descriptions of
reality, simplicity conveys two interrelated meanings, economy of
expression and economy of hypotheses, or laws. Experience has taught us
that the most useful descriptions of nature can be formulated precisely
and elegantly. We do not believe that a separate agent lies behind each
phenomenon in the physical Universe, but have come to idealize the notion,
which we can trace to William of Ockham, that a few laws that apply in the
same fashion at all times and in all places should be sufficient to
describe reality.
How are we to arrive at such laws? A style of thought that has continually
been rewarded is to take seriously great principles, to follow their
consequences to the logical conclusion and not to sacrifice them lightly.
By taking seriously Newton's theory of gravity, Adams and LeVerrier
inferred the existence of the planet Neptune from anomalies in the orbit
of Uranus. By taking seriously the law of conservation of energy, Pauli
conjectured the neutrino from the energy spectrum of electrons emitted in
radioactive beta-decay.
In such cases, the new invention is not offered as a replacement for
existing law, but as a logical outcome that must be true, if existing law
is still to hold. The operative question is not, "Can you disprove this?",
but "How could it be otherwise?".
What John Archibald Wheeler has called the "radically conservative"
strategy is the unifying theme of this elegant book by Frank Wilczek, one
of the most imaginative and wide-ranging of theoretical physicists, and
engineer-writer Betsy Devine. Wilczek and Devine characterize radical
conservatism as "conservative in its reluctance to introduce new
assumptions. … Creative tension and power is added to it by a radical
approach to the few assumptions that are adopted. These assumptions must
be formulated precisely and pushed as hard as possible. Their consequences
must be fully drawn; they must be applied to as many situations as
possible in the natural world and to the oddest and extremest conditions
we can set up in the
laboratory".
Uniformity, a second pervasive theme, is introduced by showing that we and
the stars are made of the same stuff, so we can learn in terrestrial
laboratories the physical
laws that govern the structure of the Universe, and we can apply here on
Earth what we learn by studying the heavens. The puzzles of uniformity —
why are all the fundamental building blocks the same throughout the
Universe, and why is the Universe so uniform — are raised, and our current
understanding explained.
In between, many important topics in the quest to understand the
microscopic structure of matter and the large-scale structure of the
Universe are introduced in turn. A discussion of the cosmic distance
ladder leads to Hubble's discovery of the expansion of the Universe, and
to the Big Bang. The wave-particle duality of quantum mechanics is
developed with care, and the combination of relativity and quantum
mechanics is shown to lead ineluctably to antimatter and virtual particles.
The elements of what has come to be called the Standard Model of
Elementary Particle Physics are developed in a logical and insightful
manner. Pauli's exclusion principle, which accounted for the periodic table of the
elements, and the notion of quarks lead by the radically conservative path
to the necessity of a charge of the strong interaction called 'colour',
from which it is irresistible to formulate the promising and comprehensive
theory of the strong interactions, quantum chromodynamics. The notion of
hidden symmetries is the basis for our current understanding of the weak
interaction, and prompts us to imagine more perfect worlds, in which the
full symmetry might be manifest. There the dream of a unified theory of
the fundamental interactions would be reality.
Throughout the book, the science is sound and well chosen, the writing is
graceful and the analogies are apt. I particularly enjoyed the
autobiographical interlude, "How Asymptotic Freedom Discovered Me", for
its description of the historical setting in which Wilczek and his mentor
David Gross undertook the calculations that led them to discover (at the
same time as David Politzer) that in gauge theories the effective coupling
strength could decrease at short distances or high energies. It was great
theoretical sport in the early 1970s to show that observations of deeply
inelastic scattering of electrons from protons could not be reconciled
with relativistic quantum field theory. Some players took pleasure in
proving that field theory itself must be wrong; others derived amusement
from showing that the model of the proton as a collection of quasi-free
quarks ('partons'), enunciated by Richard Feynman and others to interpret
the experiments, was inconsistent with quantum field theory and
therefore had to be incorrect. As Wilczek relates it (and it coincides
with my recollection as a spectator), the goal of the Gross–Wilczek work
was to drive the last nail into the field-theory coffin by studying gauge
theories, the class of field theories left for last because of the
technical difficulty of the calculations. These plans were dashed when they
found that in
gauge theories quarks behaved as if were free of the strong interaction, at
asymptotically high energies. They found not what they were looking
for, but
something more interesting than they
might have dared to dream. Wilczek's account is a refreshing
counter-example to the
belief that scientists always know where they are going.
Longing for the Harmonies is a fine account for the general reader of
how science is done, and of the interplay between theory and experiment
that is crucial
to progress. It gives an up-to-date picture of our struggle to understand
the
Universe as a whole, its basic constituents and the interactions among them.
It is not, however, a complete picture of the physical world. The same
themes of
uniformity and the radically conservative strategy apply, with equal
success, to
what lies in between the very large and the very small, and to phenomena
associated with collections of simple systems. Wilczek and Devine correctly
note
that "It is no small part of the charm of physics that, after more than
three
hundred years of astonishing progress, there remain absolutely major and
fundamental problems". It is no less a part of the appeal of our science
that
it has a great and growing unity. Dare we hope for a sequel in which the
phenomena that
operate on the scale of everyday experience, of condensed matter and complex
systems, are linked with those of the cosmos and the microworld?
Chris Quigg is Deputy Director for Operations of the Superconducting Super Collider
Central Design Group, Lawrence Berkeley Laboratory, Berkeley, California 94720,
USA, and Visiting Professor in the Department of Physics, University of
California, Berkeley.