21 JUNE 2007
In many ways, science is all about finding the meaning in the mysteries of math.
Physics, in particular, attempts to understand the world by matching features
in equations to properties found in physical reality. Equations that match
up well with real life are designated laws of 
nature,
and their consequences can be explored (mathematically) to predict previously
unknown phenomena. Math is like a map, pointing physicists toward new
destinations in foreign realms of reality.
So it's worth paying attention when physicists suggest that weird new things, so far hidden from view, may exist in the universe, based on nothing more than a mess of mathematical symbols. Even if the weird new stuff is a form of matter made of something other than particles.
Particle fans took a beating once before, when quantum physics came along, showing that in certain situations particles disguised themselves as waves. Nevertheless, whether your experiment finds an electron to be a particle or wave, it is still an electron, with a definite mass and other physical properties. The wave-particle dual identities are just two sides of a coin, part of a consistent quantum-math description. Think Zorro and Don Diego.
But
now imagine something unimaginable: a form of matter that conforms to
particles in no way whatsoever. Something that has no definite mass, kind
of the way a coastline has no definite length. (A coastline's length depends
on what scale you use to measure it.)
Erudite readers will immediately recognize that coastlines are an example of fractals, things that look the same at different scales of magnification. If the math describing the fundamental physical world possessed such "scale invariance," matter's basic particles could not have a single definite mass (unless that mass was zero). But that makes no sense -- it defies the very idea of particle. Many known particles do have specific non-zero masses. So a "scale invariant" form of matter would not be made of particles, says Harvard physicist Howard Georgi.
"Scale invariant stuff, if it exists, is made of unparticles," he writes in a paper recently published in Physical Review Letters.
Now, matter made of "unparticles" sounds unthinkable. "It is a little hard to even talk about the physics of something so different from our familiar particle theories," Georgi concedes.
But suppose there is something more to reality. If the math allows it, it might be there. And, as Georgi notes, some math does seem to allow it, as described in a 1982 paper by Tom Banks and A. Zaks.
In the standard theory, particles are made from "matter fields" found throughout space. Particles appear where a field has twisted itself up into something like a knot. Now suppose there exist other kinds of fields (Banks-Zaks fields), hidden from detection because they interact very weakly with the standard fields (and particles). It may be that the true whole theory of reality includes both the current standard fields plus these unknown unparticle fields.
Presumably the standard and unparticle fields would interact by the exchange of particles so massive that they have not yet been produced in any human experiments (which is why we have been unaware of the unparticles' existence).
Soon, though (like next year), a new atom smasher will begin operations outside Geneva, Switzerland, possibly with enough power to reach the energy needed to reveal the unparticle stuff. When particles collide, they produce a mishmash of debris, possibly containing particles never before discovered. (The builders of this smasher, known as the Large Hadron Colider, have some particular new particles in mind, such as the famous Higgs boson.)
A simulated event of the LHC (Large Hadron Colider)
at CERN near Geneva, Switzerland. Photo:
CERN
Physicists analyzing the collisions try to make sure that the energy of all the debris particles adds up to the energy going into the collision. If the debris energy doesn't add up -- that is, if some of the energy goes missing -- the logical conclusion is that something invisible has carried some energy away.
By Georgi's calculations, that is exactly what unparticle stuff could do. If unparticle stuff is responsible for the missing energy, that energy would appear to have been carried away by a fractional number of invisible particles.
So unparticle stuff is not simply a wild science-fiction suggestion without tangible consequences. "We can predict interesting features of unparticle production that serve as experimental tests of this crazy possibility," Georgi writes.
Finding unparticle stuff is a long shot, as Georgi acknowledges. But if physicists really want to understand reality, they can't dismiss crazy ideas out of hand. Despite the enormous progress of physics over the past century, every expert knows that some major aspects of reality await discovery -- some unknown form of glue is required to fit the pieces of current scientific knowledge seamlessly together.
If unparticle stuff is this glue, it might have important implications for understanding the history of the universe and its current curious behavior. And maybe unparticle matter could have practical consequences too -- that is, some way to make money out of it. No time soon, for sure, but in future centuries -- the way today's economy depends on the electromagnetic revelations of the 19th century and the quantum revolution of the 20th.
But practically relevant or not, the unparticle possibility reminds us that science is not a closed textbook to be memorized, but an unfinished guidebook for exploring new realms and discovering new realities. The roadmap provided by mathematics has not yet been completely unfolded.
E-mail: tsiegfried@nasw.org
