We know that the path followed by the light from point A to point B is independent of the direction of propagation of light. This is what is called in French "le principe de retour inverse de la lumière". What do we call this in English scientific terms?

  • $\begingroup$ Do you mean "reciprocity"? en.wikipedia.org/wiki/Reciprocity_(electromagnetism) $\endgroup$
    – CuriousOne
    Jan 26, 2016 at 8:21
  • $\begingroup$ I guess it is, but it sounded too complicated for me to assure it fits the context I'm concerned with $\endgroup$
    – YoussefDir
    Jan 26, 2016 at 8:27
  • $\begingroup$ OK... given John Rennie's answer I am not sure that I have what you are looking for. $\endgroup$
    – CuriousOne
    Jan 26, 2016 at 8:42
  • $\begingroup$ My 9th grade physics text in the chapter of refraction simply says Principle of Reversibility of the path of light. $\endgroup$
    – N.S.JOHN
    Jan 26, 2016 at 9:12

1 Answer 1


I don't think there is a universally agreed phrase to describe this, but I think the closest is the principle of geometrical reversibility.


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