that comprise our universe, the photons and quarks and gluons and elec-
trons and neutrinos of the Standard Model, the particles? Why do they
have the masses and interaction strengths that they do? These questions
are beyond the scope of the Standard Model. The Standard Model is a ta-
ble of “what” that enables us to predict “how”—but completely unad-
dressed is the question of “why.”
Possibly, “why” is a question lurking beyond the realm of physics—but
maybe not. The last century has seen science’s view of the fundamental
particles change first from atoms to neutrons, protons, and electrons, and
then to the particles that comprise the Standard Model. Perhaps there
are even more fundamental particles that make up those in the Stand-
ard Model. The leading candidate theory in this area is string theory^7
(and a more evolved version, known as superstring theory), which postu-
lates that all the particles in this universe are the vibrational modes of
one-dimensional objects known as strings. A violin string of a fixed
length and tension can be made to vibrate only in particular patterns.
When a violinist draws a bow over a single string, the sound is melodi-
ous, rather than the caterwauling of discordant sounds. That is because
each vibrational pattern corresponds to a particular note. The strings that
comprise string theory can vibrate only in particular patterns—and these
patterns are the particles that comprise our universe.
The strings that lie at the heart of these theories are incredibly tiny^8 —
direct observation of strings is as difficult as trying to read the pages of a
book from a distance of 100 light-years. This certainly appears to rule out
the possibility of direct observation, but science does not always need di-
rect observation; often, consequences suffice. Scientists had not actually
seen an atom until revealed by the scanning microscopes of the 1980s,
but the atomic theory was firmly in place more than a hundred years be-
fore that. Much effort is being expended to find predictions that string
theory makes that could be experimentally or observationally verified.
However, string theory is itself a work in progress, and as it goes through
various incarnations (there have been at least four generations of string
theory so far), the predictions change.
Nonetheless, string theory generally makes two types of predictions
that transcend the Standard Model: it predicts particles that have yet to be
observed, and geometrical and topological structures for the universe
that remain unverified. Both of these merit a look—not only because they
are fascinating in and of themselves, but because it is possible that some
future theory may show us that these lead to contradictions, and we shall
have to look elsewhere.
I was fortunate to attend a lecture several years ago at Caltech given by
Space and Time: Is That All There Is? 141