I have been performing some experiments with the double slit quantum eraser. I mark the "which way" path with linear polarizers (arranged orthogonally) before the red laser light passes through the double slit. When I perform the experiment without the quantum eraser (when a "particle" pattern is observed), the laser pattern still appears red on the wall. However, how would "red" be conveyed if the light is acting as a particle? Shouldn't it not carry a "red" wavelength if it is a particle? Could it be something to do with it being absorbed and re-emitted by the wall as a wave at that point?

A similar question was somewhat covered here, but not directly asked or addressed:

Light wave particle duality

  • $\begingroup$ The nature of light doesn't change just because your experiment changes. The only thing that the difference in your setup affects is what data you obtain from the experiment; the entire photon wave function is present in all cases. $\endgroup$
    – Asher
    Nov 9, 2017 at 16:37

1 Answer 1


If you look at photon as a particle - it has energy. Red photon has energy of ~1.95 eV.

Arguably, photon energy is more important than wavelength of the light. Photon interaction with matter happens on scales which are much smaller than visible light wavelength, hence it's energy is what causes photons of different energy (=color) to react with matter differently (i.e. activate different cone cells with different probabilities).

  • $\begingroup$ Thank you for the answer, it really has me thinking! I am curious what would cause that amount of energy to manifest itself as color instead of brightness? $\endgroup$
    – Jonathan
    Nov 9, 2017 at 17:02
  • $\begingroup$ By the way, interesting that you have 42 "answer to everything" reputation and 5 gold medals :-) $\endgroup$
    – Jonathan
    Nov 9, 2017 at 17:05
  • 1
    $\begingroup$ @Jonathan Brightness is related to the number of photons. Consider you have small red apples and larger green apples. Then you can have a bucket of red apples or a bucket of green apples. These would correspond to red and green light. Or you could have a twice larger bucket of red apples. It would correspond to brighter red light. $\endgroup$
    – safesphere
    Nov 9, 2017 at 20:04

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