Robert McNees
Astronomer and mathematician Pierre-Louis Moreau de Maupertuis, exact date of birth unknown, was born around this time in 1698 and baptized #OTD.
He was among the first to articulate the Principle of Least Action, one of the most beautiful ideas in physics.
Image: Wellcome Trust
Robert McNees
Maupertuis originally formulated his principle to explain the motion of light, arguing that the integral of its velocity along the path it follows is minimized.
This allowed him to recover Snell's Law for the refraction of light as it passes between different materials.
Robert McNees
By 1744, Maupertuis extended this idea to the motion of material objects.
He defined an object's “action" as the integral of momentum along its path, or the time integral of its "vis viva" (2 x kinetic energy) from start to finish.
Maupertuis proposed that Nature acts to minimize this quantity.
Robert McNees
(Leonhard Euler proposed a very similar idea around the same time, but ceded priority to Maupertuis. Konig claimed they both swiped the idea from Leibniz, who probably came up with the same principle decades earlier. But Leibniz only discussed it in private letters, so how were Euler and Maupertuis supposed to know?)
Robert McNees
In 1746 Maupertuis presented his paper “Laws of Movement and Rest” to the Berlin Academy of Sciences, applying his principle to the motion of point masses.
In his subsequent essay “The Laws of Rest and Motion Deduced from the Attributes of God,” Maupertuis gave a statement of the principle of least action that is often quoted or paraphrased. (5/n)
Robert McNees
He later tried to apply his principle in other fields including biology, theology, and psychology (he proposed a principle of pleasure and pain). Those efforts didn't meet with quite as much success!
Lagrange and later Hamilton would generalize and refine the principle in important ways, but we usually credit Maupertuis with originating the Principle of Least Action. (6/n)
Robert McNees
Anyway, that 1746 paper by Maupertuis is probably the oldest work that I have cited in one of my own publications. (7/7)
https://arxiv.org/abs/0803.1485
MotionMountain
Theprinciple of least action remains the first of the nine lines that describe all of nature:
https://www.motionmountain.net/9lines.html
"Action" is the physical quantity describing change. It measures how much a system changes. The work of Dirac and BPR leads to a microscopic model of action based n 3d geometry and topology.
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