Posted by: T. Boyd | December 9, 2009

The Story of Quarks

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.


From WikiPedia: Quarks

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)

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  1. While a graduate student at U. Ga., I was teaching an accelerated physics lab course for undergraduates. One group elected to study the Millikan oil drop experiment. In Millikan’s own work, he had a few data that indicated fractional charges consistent with 1/3 electron charge (quarks). I challenged the undergrads to find such rare charges. They did not find any, but it made for an exciting lab for them, I think.

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