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No. 115: Jan-Feb 1998

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Splitting The Electron's Charge

We all know that the atom can be split, but the electron's charge? No way! R.A. Millikan's oil-drop experiments, circa 1911, demonstrated conclusively that the basic, indivisible unit of electrical charge was that on the electron. Later, an exception was made for those quarks that are firmly locked up inside nuclear particles. They each have 1/3 the electron's charge -- but they never, never escape to the outside world.

It was, therefore, counterintuitive when R. Laughlin proposed in 1982 that fractional electrical charges actually could show up elsewhere in physics. The phenomenon that suggests this possibility is the Fractional Quantum Hall (FQH) effect. Physicists reluctantly accepted the likelihood of fractional charges in this well-verified phenomenon; but the experiments demonstrating fractional charge were a bit esoteric -- the fractional charges were not "palpable" enough.

Two new experiments have made fractional charges much more tangible. When a layer of electrons, held just above absolute zero, is subjected to a powerful magnetic field, you can almost "hear" the fractional charges. The signals from these experiments have been likened to hail hitting a tin roof. Just as you can gauge the size of hailstones from their impact, so you can estimate the electrical charges involved in these experiments -- they are 1/3 that of the electron.

(Ehrenstein, David; "Slicing an Electron's Charge into Three," Science, 277:1766, 1997. Also: Kane, Charles L., and Fisher, Matthew P.A.; "A Shot in the Arm for Fractional Charge," Nature, 389:119, 1997.)

Comment. Is there nothing in the subatomic world that is indivisible?

From Science Frontiers #115, JAN-FEB 1998. � 1998-2000 William R. Corliss