The Story of Quarks
(Also posted with an image on the blog)
December 9, 2009
I asked my bride (of 30 years) which science story of the 20th century
would interest her the most, meaning, of course, which physics story,
since that is what I am most comfortable talking about. I gave
her a choice of the discovery of electrons, protons, neutrons, or
quarks, and briefly described each story to her.
Her eyelids were very heavy toward the end of my recital. She
said what she enjoyed most was my animated face as I expressed my
enthusiasm for those discoveries. And then she asked me to
explain more about quarks, so I thought I would write about them (I
pronounce it, like all good Texans, as “quorks”, on which she
tried to correct me).
The quark story begins about 50 years ago, when protons, neutrons, and
electrons were thought to be the fundamental particles of matter,
although other types of particles were being found in cosmic rays and
from the high energy accelerators. By 1960 about 24 different
“elementary” particles had been found with puzzling properties.
In 1956, Murray
Gell-Mann proposed that there were even more fundamental particles
named quarks which combined in various ways to make up many of the
members of this “particle zoo”, as it was called. In 1968,
high energy electrons were made to penetrate protons and showed that
there were point-like objects inside the protons that interacted with
these probing electrons. The experimenters seemed to have found
quarks.
It was decided that a proton is composed of two “up” quarks, each
having a +2/3 charge, and one “down” quark with -1/3 charge,
where the unit of charge is +1 for a proton, and -1 for an electron. On
the other hand, the neutron consists of one “up” quark and two “down”
quarks, with a net charge of zero.
And, the theory,
which has been supported by experiments, says that all of the various
members of this class of particles known as hadrons (now numbering
about 33) are made up of six different “flavors” of quarks and their
anti-particle twins. The six quarks are named: up, down, charm,
strange, top, and bottom.
It seems that the force that binds the quarks together in these various
particles is so strong that the quarks cannot be forced apart.
This is predicted by the theory, and thus far experiments to split the
protons or neutrons into quark components have failed.
Isn’t it fascinating that even with such tiny things as protons and
neutrons, scientists are able to find still smaller particles like
quarks, demonstrating once again the wondrous complexity of God’s
creation.
For you formed
my inward parts; you knitted me together in my mother’s womb. I
praise you, for I am fearfully and wonderfully made. Wonderful are your
works; my soul knows it very well. (Psalm 139:13-14)
You can write Boyd at BrightMysteries@verizon.net