In physics, a Dirac string is a fictitious one-dimensional curve in space, conceived of by the physicist Paul Dirac, stretching between two Dirac magnetic monopoles with opposite magnetic charges, or from one magnetic monopole out to infinity. The gauge potential cannot be defined on the Dirac string, but it is defined everywhere else. The Dirac string acts as the solenoid in the Aharonov-Bohm effect, and the requirement that the position of the Dirac string should not be observable implies the Dirac quantization rule: the product of a magnetic charge and an electric charge must always be an integer multiple of . The magnetic flux running along the interior of the string maintains the validity of Maxwell's equations. If Maxwell equations are modified to allow magnetic charges at the fundamental level then the magnetic monopoles are Dirac monopoles no longer and do not require attached Dirac strings.
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“The Indian remarked as before, “Must have hard wood to cook moose-meat,” as if that were a maxim, and proceeded to get it. My companion cooked some in California fashion, winding a long string of the meat round a stick and slowly turning it in his hand before the fire. It was very good. But the Indian, not approving of the mode, or because he was not allowed to cook it his own way, would not taste it.”
—Henry David Thoreau (1817–1862)