A shake is an informal metric unit of time equal to 10 nanoseconds, or 10−8seconds.[1] It was originally coined for use in nuclear physics, helping to conveniently express the timing of various events in a nuclear reaction.
The phrase "a couple of shakes", in reference to the measurement of time, may have been popularized by Richard Barham's Ingoldsby Legends (1840);[2] however, the phrase was already part of vernacular language long before that.[3]
Nuclear physics
For nuclear-bomb designers, the term was a convenient name for the short interval, rounded to 10 nanoseconds, which was frequently seen in their measurements and calculations: The typical time required for one step in a chain reaction (i.e. the typical time for each neutron to cause a fission event, which releases more neutrons) is of the order of 1 shake, and a chain reaction is typically complete by 50 to 100 shakes.[4]
See also
Barn, a companion unit of cross-sectional area created by the same people, for the same general purposes, at the same time (the measured value of nuclear-reaction cross section was larger than expected, hence deemed "as big as a barn").
↑Richard Harris Barham (1840). "The Babes in the Wood". The Ingoldsby Legends. p.191. I'll be back in a couple of shakes. Also on page 212 ("A Row in an Omnibus") "in a brace of shakes" and on page 247 ("The Lay of St. Alois") "in a couple of shakes". But the phrase appeared in print before Barham; see for example James Edward Alexander (1833). Transatlantic Sketches. p.284.
↑Cochran, Thomas B. (10 April 1994). "Hydronuclear Testing or a Comprehensive Test Ban?"(PDF). Washington, DC: Natural Resources Defense Council. p.4. Archived from the original(PDF) on 2008-12-06. The period, 10−8 seconds, turns out to be a convenient unit of time, and it was defined during the Manhattan Project as one 'shake'.
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