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The Three Families of Matter
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16970 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
4 / 1990 |
3,450 Words |
| Author
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Richard L. Lewis
Richard L. Lewis is a biochemist currently working as a free-
lance science writer in New York. |
Most children eventually get an overwhelming urge to pull something apart and find out what it's made of and how it operates. While this impulse might fades in some, in a certain type of scientist it matures in the relentless smashing of the atom into smaller and smaller components with the same questions in mid: What's inside? How does it work?
The closing months of the last decade established yet another milestone in this quest with an announcement at the Stanford Linear Accelerator Center (SLAC) in California on October 12, upstaging the European Center for Particle Physics (CERN) in Geneva, which planned to go public with the same findings on October 13.
According to the historic pronouncement, scientists had firmly established that there are only three fundamental families of subatomic particles. This is a welcome achievement because, before October 12, there was annoying uncertainty regarding how many families there might be, a frustrating thought for those looking for simplicity.
This accomplishment, of course, is just the latest step in a long search that can only be considered to have been carried out on the firm foundation of experiment since the nineteenth century.
History of Smashing Matter
After John Dalton replaced the alchemical mysteries with the atomic theory of matter in 1808, the atom its name derived from the Greek for "cannot be cut" - reigned for almost a century as the indivisible, unchangeable stuff of the material world.
In 1897, J.J. Thompson of Cambridge University dethroned the pretender with his discovery of the electron, an electrically charge fragment torn out of the “cannot be cut" atom (though the latter kept the name). Later experiments demonstrated the existence of the proton, 1,800 times more massive than the electron but exactly the opposite charge; and the neutron, which is just a fraction heavier than the proton but with no electric charge.
While a neutron is quite stable within an atomic nucleus, in isolation it falls apart in about 10 minutes into seemingly just a proton and an electron. It was the close study of this breakup that led to the discovery of the fourth and last of the "regular" particles, the neutrino - or, more specifically, the electron neutrino. Though predicted to exist in 1933, this
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