Most physicists believe we have already
discovered the smallest particles that exist, the basic building blocks
of nature. However, this isn’t the first time scientists thought they’d
reached bottom, the ultimate limit of minuteness.
The ancient Greeks believed everything was made from four constituents: air, water, fire, and earth. How primitive.
Later, people believed everything was made of atoms of 92 different elements.
Then science discovered atoms had two parts: nuclei surrounded by electrons.
After that, we learned that nuclei were
made of protons and neutrons. And even later, physicists decided those
were probably made of “up” and “down” quarks.
But more particles were discovered,
ultimately leading to a final tally of 16 “fundamental” particles that
comprise nature’s irreducible pieces that are believed to have zero size
and no internal structure. Everything else we see around us is made of
combinations of these fundamental particles.
Oops, with the discovery of the Higgs
boson, let’s make that 17 fundamental particles. Oh, and 12 of the 17
particles have corresponding antiparticles; the other 5 are their own
To recap: in 25 centuries of peeling
layer after layer of the cosmic onion, we’ve gone from 4 basic building
blocks, to 92, to 2, to 3, and finally to 17+12. Great progress! (?)
But are we really smarter than the ancient Greeks? Maybe not.
Perhaps, some theoretical physicists say, the
16 17 fundamental particles are actually made of “+” and “0” preons (and two antipreons: “-” and “0”). They say “+” preons have an electric charge of +⅓, and “0” preons have zero charge.
The compositions and masses of some known particles are:
Mass Relative to Electron
electron - - -
up quark ++0
W+ boson +++000
One might ask how the preon idea explains
the enormous range of masses. If three “0” preons (e-neutrino) have
zero mass, mustn’t each “0” preon have zero mass? If so, the two “+”
preons in the up quark should each have a mass of 2, which would make
the W+ mass 6 instead of 157,339. And how can nine preons (proton) weigh
86 times less than six preons? A person who would ask such
questions hasn’t met any theoretical particle physicists, who are
unsurpassed at mathematical crazy glue and duct tape. The more
forthcoming ones say if this “seems like a bit of hand waving, it is.”
Of course, what is shown above isn’t the
only alternative. In fact, there are more versions of preon theory than
there are preon theorists.
I should mention one minor detail: all
experiments to detect preons have come up empty. Anything made of
something else can’t have zero size. While it’s impossible to prove that
the size of anything is exactly zero to a zillion decimal
digits, we do know that quarks are no larger than 1/5000th of the size
of a proton, which has the smallest measured size. Theorists aren’t
worried that there’s no evidence for their ideas, that just a reason to
build bigger accelerators.
As an experimental physicist, I am
innately skeptical of the latest theory-du-jour. Less than 1% of such
whimsies are ultimately confirmed experimentally. But even the most
skeptical must admit that progress in science, and ultimately for
society, has often come when crazy ideas were proven true. Nothing
shocked the sensibilities of the physics world more than Einstein’s
revolutionary ideas. His success will provide cover for countless
off-the-wall theories for centuries to come.
Indeed, the great physicist Wolfgang
Pauli once said: “There’s no question this idea is crazy. But, is it
crazy enough to be true?”
If preons are eventually discovered, the next question will be: “What are preons made of?”
January 7, 2013
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