Fermat's principle of least time is only an approximation valid in the high-frequency limit
the verdict
SUPPORTED
the evidence backs this
confidence 92/100
Fermat's principle of least time and related geometric optics formulations are well-known approximations that break down when wavelength or diffraction effects become non-negligible at lower frequencies.
Evidence for · 3
Gravitational Lensing from a Spacetime Perspective
2004 · cited by 498
This paper reviews light propagation and spacetime perspectives where geometric optics and least time approximations are bounded by more general wave and geodesic descriptions.
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More for · 2
Lensing of gravitational waves: Efficient wave-optics methods and validation with symmetric lenses
2023 · cited by 58
This paper discusses how wave-optics effects become dominant at low frequencies, contrasting with the high-frequency geometric optics regime.
Propagation of polarized gravitational waves
2021 · cited by 52
This paper notes that geometric optics approximations for wave propagation fail at large but finite frequencies, requiring wavelength-dependent corrections.