Casimir effect


Cas·​i·​mir effect
: an attractive force created by the net action of virtual photons on physical objects in close proximity
Although no one has yet seen negative matter or negative energy in the wild, it has been detected in the laboratory, in the form of something called the Casimir effect. Consider two uncharged, parallel plates. Theoretically, the force between them should be zero. But if they are placed only a few atoms apart, then the space between them is not enough for some quantum fluctuations to occur. As a result, the number of quantum fluctuations in the region around the plates is greater than in the space between. This differential creates a net force that pushes the two plates together.Michio Kaku, Discover, December 2004

Word History


after Hendrik B.G. Casimir †2000 Dutch physicist

Note: The initial report on the effect was published by Casimir in "On the attraction between two perfectly conducting plates," Proceedings van de Koninklijke Nederlandse Academie van Wetenschappen, vol. B51 (1948), pp. 793-95.

First Known Use

1988, in the meaning defined above

Time Traveler
The first known use of Casimir effect was in 1988

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Dictionary Entries Near Casimir effect

Cite this Entry

“Casimir effect.” Dictionary, Merriam-Webster, Accessed 7 Jun. 2023.

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