You are watching: Does light always travel in a straight line

Everything move in geodesics if not acted on by a pressure other than gravity -- this is one axiom of general relativity (the geodesic equation). Geodesics space straight lines in the lack of heaviness -- this is part of the other axiom of basic relativity (the Einstein-Hilbert action, or the EFE or whatever).

Light doesn"t communicate much with everything, except quite weakly through gravity, and with some assorted scattering patterns, choose those which permit you come actually see things, however those are fairly pointy (reflection, refraction, etc. -- the courses are pointy as long as the scattering border is sharp), so you still check out a bunch of right lines.

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edited might 26 "18 in ~ 5:28

reply Jul 19 "13 in ~ 4:25

Abhimanyu Pallavi SudhirAbhimanyu Pallavi Sudhir

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It is an axiom of basic relativity. A an easy assumption. A much more accurate statement would be that light constantly travels along a spacetime geodesic. The classical addition of speeds in newtonian meachanics doesn"t work inrelativity (light is the most excessive case). The is the source of every weird ingredient in relativity

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edited Jul 19 "13 in ~ 3:45

answer Jul 19 "13 at 3:00

user16007user16007

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The straightness of irradiate rays follows from constructive interference of tide that approximately follow the shortest path (or more generally an extremal path).

Around the extremal route the derivative of the path length wrt variations of the route is 0. Therefore approximately extremal courses all have the same length and thus the very same phase do waves adhering to them interfere constructively. Paths approximately non-extremal path interfere destructively and also waves complying with them cancel out. This explanation applies classically to the EM field and Maxwell equation, or quantum mechanically to field of amplitudes. This is likewise the explanation the Huygen"s principle.

Feynman offers a detailed explanation of this in *QED, the strange theory of light and also matter* and also in his great notes and also other places.

The an exact statement should be that light in totally free space moves in right lines and consistent velocity wrt inertial reference frames. The does not relocate in straight lines or continuous velocity in accelerating reference frames or in no homogeneous media.

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The fact that the rate of light is elevation of the observer"s velocity is a relativistic effect. Formally the is a postulate of special relativity.