Scientists gathered in Rio for the LAFEX International School in
High-Energy Physics are paying close attention to an extraordinarily
rare form of matter. They are hearing reports from modern explorers
representing more than eight hundred physicists and students from
Brazil, Canada, Colombia, France, Italy, India, Japan, Korea,
Mexico, Russia, Taiwan, and the United States, who are engaged in
the quest to find the top quark and measure its properties.
While debating the evidence for top, charting the next round of
experimental studies, and theorizing about what it all means, the
participants in LISHEP95 are living out a revolution in our
perception of nature: our human dimensions are not favored over
others for experiencing and comprehending the physical universe.
An astonishing aspect of nature’s richness is that whenever we
explore an unfamiliar regime of distance, or time, or energy, we
find new and interesting phenomena. Ours is not a universe of
Russian dolls! When we study matter under unusual conditions,
surprises are everywhere—from the superconductivity exhibited by
many materials at very low temperatures to the new forms of matter
created in particle accelerators at very high energies.
Poets speak of attaining some distance from the world—finding some
strangeness—to express the truths that make a rock stony or a love
sublime. Like the poet, the physicist seeks seek not merely to name
the properties of nature, but to plumb their essence. To truly
understand the world around us, to fully delight in its marvels, we
must step outside everyday experience and look at the world through
new eyes.
Physicists have known since the 1920s that to explain why a table is
solid, or why a metal gleams, we must explore the atomic and
molecular structure of matter. That realm is ruled not by the
customs of everyday life, but by the laws of quantum mechanics. The
hunt for the top quark reported in Rio makes us think anew about how
the microworld influences our surroundings.
It is popular to say that top quarks were produced in great numbers
in the fiery cauldron of the Big Bang some fifteen billion years
ago, disintegrated in a fraction of a second, and vanished from the
scene until my colleagues learned to create them in a giant
accelerator near Chicago. That would be reason enough to be
interested in top: to learn how it helped sow the seeds for the
primordial universe that has evolved into the world of diversity and
change we live in. But it is not the whole story, and it invests
the top quark with a remoteness that hides its real importance to
our lives.
The real wonder is that here and now, every minute of every day, the
top quark affects the world around us. Through the uncertainty
principle of quantum mechanics, top quarks and antiquarks wink in
and out of an ephemeral presence in our world. Though they appear
virtually, fleetingly, on borrowed time, top quarks have real
effects.
A few numbers determine the dimensions and character of the everyday
world, from the size of atoms to the energy output of the sun. Only
a generation ago, these parameters of the quotidian—the mass of the
proton, the mass of the electron, and the strengths of the
fundamental interactions—seemed givens, beyond the reach of science.
Today, we have begun to discern links among them. We see how each
of them might be understood in principle, and even computed.
Of most pressing concern to particle physicists is top’s influence
on the the weak force. The next crucial test will come from precise
measurements of the masses of the top quark and the W-boson, the
carrier of the weak force. If they stand in the predicted relation,
we will have new confidence that we understand how the top quark
influences our world. And our everyday world it is, because the
weak force governs not only the rate of radioactive decay but also
the intensity of the sun’s rays on Copacabana beach.
In fact, the mass of the top quark is encoded in the strengths of
all the forces that rule the everyday world. We believe that the
strong, weak, and electromagnetic forces all have equal strengths at
some very high energy called the unification energy. The
differences we observe in our low-energy world arise because the
interactions evolved differently as the universe cooled. The way
each one evolved depends on the character of the forces themselves
and on the spectrum of particles that appear from very high energies
down to the energy scale of common experience. Because the top
quark stands apart as very much heavier than the other quarks, it
has a special influence.
But that is not all. The proton’s mass is determined mostly by the
energy stored up in the force that holds together the up and down
quarks that make up the proton. The strength of the force between
quarks is influenced by the top quark. The top quark is not a
constituent of the proton, but if top weighed ten times more or
less, the proton mass would shift up or down by about twenty
percent. This world—our world—would have a very different
character.
While particle physicists work far from the domain of everyday
experience to establish the properties of the top quark, we can
savor the realization that those properties are encoded in the form
of every flower and grain of sand, in every human face. Top
matters!