Two-slit, you are simply stunning

September 6, 2002

The most beautiful experiment in physics involves passing single electrons through a double slit in a demonstration of quantum mechanics.

Readers of the magazine Physics World and the website slashdot.org voted for their favourites in a poll carried out by Robert Crease, a historian at the Brookhaven National Laboratory in the US.

While a great range of different experiments was proposed, it came out a clear winner.

In the experiment, a stream of electrons passes through two slits and forms an interference pattern on a screen - behaviour that in classical physics is supposed to happen only with waves and not with particles. It exemplifies wave-particle duality and quantum mechanics itself.

"The double-slit experiment with electrons possesses all of the aspects of beauty most frequently mentioned by readers," Dr Crease said.

He added that it could convince the most die-hard sceptics of the truth of quantum mechanics.

Alison Campbell, an astronomer at St Andrews University, said the impact of carrying out the experiment was tremendous. "Seeing the two-slit experiment is like watching a total solar eclipse for the first time: a primitive thrill passes through you and the little hairs on your arms stand up," she said.

Galileo's experiment on falling bodies was voted in second place, with Millikan's oil-drop experiment to weigh the electron third.

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