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By Young's double slit experiment it was clearly proved that light was not a rectilinear beam of photons an assumption made by Issac Newton. BUT we still consider light to be a straight beam and we always call them light rays what's wrong in calling them light waves?

I know that it is known light has dual nature but still it is obvious that it has wave like nature.

Nikolai Romanov Belliovichksky
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  • One uses what is needed for a particular problem. Rarely does an optics designer use straight beams, instead they would use Gaussian optics or more complex techniques as needed. – Jon Custer May 29 '22 at 17:26
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    "we consider light as a rectilinear stream of photons" as seen in this double slit experiment one photon at a time, light is not a rectilinear stream of photons. Photons are quantum entities and follow the rules of quantum mechanics, the classical EM wave built up in a complicated way by the photons. https://www.sps.ch/artikel/progresses/wave-particle-duality-of-light-for-the-classroom-13/ my answer here https://physics.stackexchange.com/questions/90646/what-is-the-relation-between-electromagnetic-wave-and-photon/90649#90649 . – anna v May 29 '22 at 17:35
  • In many applications like basic optics and/or power or intensity per area the ray model is just fine. The wave model is equally fine for example why does light have color? – PhysicsDave May 29 '22 at 22:23

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The point is that even though everything has a wave(function) nature, the form of this wave depends on its physical situation. The wave form of a laser pulse is very peaked around a beam whereas in your situation is quite wide. This wave form only represents the probability of finding an individual (point) photon at some place though. However because of the huge amount of photons you have in your typical light source is, to very good approximation, treated just like a "normal" wave.

FriendlyLagrangian
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