51�Թ�

In Chiang’s story, this discovery is prompted by a breakthrough in alien physics: the heptapods don’t understand algebra, but they understand the variational calculus behind Fermat’s principle, which dictates that a ray of light always travels the shortest possible distance between two points.

Chiang writes with a gruff and ready heart that brings to mind George Saunders and Steven Millhauser, but he’s uncompromisingly cerebral: “Story of Your Life” contains explanations of variational calculus, charts that illustrate the mathematician Pierre de Fermat’s principle of least time, and sentences like “The sound spectrograph for ‘heptapod eats gelatin egg’ was analyzable.”

Fermat’s principle is “purposive, almost teleological.”

DuBridge is a radiantly friendly, free & easy lecturer who, pupils swear, can make Fermat's Principle seem as simple as rolling off a logarithm.

Now the direction and phase of the light are those of the ray which reaches the eye; and by Fermat's principle, established by Huygens for undulatory motion, the path of a ray is that track along which the disturbance travels in least time, in the restricted sense that any alteration of any short reach of the path will increase the time.