[Physics] In scattering, how does a particle ‘know’ which direction it is being illuminated from


In scattering experiments, for example light scattering, the scattering strength from different sized particles is depicted as below.

Scattering examples

What I can't understand is: how does a particle know which direction the light is coming from and therefore which direction to bias the scattering (as in the case of large particles)? For instance, if we are just thinking about the electron oscillations, don't they just occur perpendicular to the light source?

So in my example below, I have a particle being illuminated from the left, and one from the right. If we were to look at JUST the electron oscillations inside particle, wouldn't they be doing the exact same thing? So how does the scattered wave seem to 'know' where 0 degrees is in relation to the incoming beam?

For clarification I am not talking about the angular dependent interference due to Rayleigh or Mie scattering. I hope this makes sense.

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Best Answer

It is momentum that defines the incoming direction and momentum transfer the outgoing one.

The photons, quantum mechanically carry momentum equal to p=h*nu/c . Momentum is a vector and defines directions.

An electromagnetic field is an emergent classical quantity built up by innumerable photons.

There exists also a momentum defined for the classical field where the Poynting vector defines the direction, if one ignores the quantum dimensions, but you are talking of electrons which are quantum mechanical elementary particles.

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