Symbol n_1
is part of the quantity the equation computes from the expression on the right.
Read this term in its guide →Published equation contexts
Why this formula appears here
A beam of light crossing from air into glass bends at the interface by exactly the angle that gets it through in the least possible time. Pierre de Fermat stated this as a principle in the 1660s, and the consequence collapses into one line of algebra: for a ray crossing between two media of refractive index and , . Snell’s law, in other words, is not an independent fact about glass. It is what falls out of a single global stipulation — least time — applied to one path among infinitely many. Pierre-Louis Maupertuis generalized the same move to all of mechanics in the 1740s, proposing that nature always acts by the smallest possible “action,” and Euler, Lagrange, and…
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Symbol theta_1
thet is part of the quantity the equation computes from the expression on the right.
Read this term in its guide →Symbol n_2
is an input to the expression that computes the quantity on the left.
Read this term in its guide →Symbol theta_2
thet is an input to the expression that computes the quantity on the left.
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Read it with the definitions, units, and assumptions supplied by the article.
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Published contexts (1)
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Equation 3 · Einstein & Evolution
Physics Optimizes, Evolution Satisfices: Two Kinds of Perfection
This equation states an equality: the expressions on both sides have the same value under the article’s assumptions.
A beam of light crossing from air into glass bends at the interface by exactly the angle that gets it through in the least possible time. Pierre de Fermat stated this as a principle in the 1660s, and the consequence collapses into one line of algebra: for a ray crossing between two media of refractive index and , . Snell’s law, in other words, is not an independent fact about glass. It is what falls out of a single global stipulation — least time — applied to one path among infinitely many. Pierre-Louis Maupertuis generalized the same move to all of mechanics in the 1740s, proposing that nature always acts by the smallest possible “action,” and Euler, Lagrange, and…
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