# What actually is scattering?

What actually is scattering? What do we mean when we say "light is scattered by particles in air,..."?

I can understand reflection/refraction and am quite experienced with ray optics.

I just want to know the basic understanding of what actually is happening with the wave. How is it any different from an irregular reflection in a broader sense?

• in this sense - I would say it is whatever happens to the light and changes it's direction – jaromrax Feb 6 '17 at 17:52
• As @jaromrax mentions, it comprises reflection and refraction. But you are missing an important point: difraction. With geometric optics it is difficult to capture diffraction, and you shall consider physical optics (or whatever people call it). You might want to check this paper, though, - Keller, J. B. (1959). The geometric optics theory of diffraction. In The McGill Symposium on Microwave Optics (Vol. 2, pp. 207-210). – nicoguaro Feb 6 '17 at 19:39

## 2 Answers

In classical mechanics, the basic scattering process is illustrated with two billiard balls hitting each other. It is called a scattering because there is a change of direction and a transfer of energy.

In light scattering it is the change in direction of the energy that the light carries, an extension of the classical mechanics concept.

Light scattering is a form of scattering in which light in the form of propagating energy is scattered. Light scattering can be thought of as the deflection of a ray from a straight path, for example by irregularities in the propagation medium, particles, or in the interface between two media. Deviations from the law of reflection due to irregularities on a surface are also usually considered to be a form of scattering. When these irregularities are considered to be random and dense enough that their individual effects average out, this kind of scattered reflection is commonly referred to as diffuse reflection.

In quantum mechanics the scattering of particles from each other and off fields is described by quantum mechanical equations, where only the probability distribution of the scattered products can be calculated and checked against measurements. For example the quantum mechanical of photon off a nucleus. Feynman diagrams help in these calculations.

• +1 great answer. I think mentioning the concept of the wave packet might add value to it. – Wolpertinger Feb 6 '17 at 21:15
• So, what is the mathematical interpretation? Only through quantum mechanics? How would Rayleigh Scattering, for example, be explained mathematically given that scattering is just a term used to define "random" deviations of light due to collisions with particles in air. Is it good enough to say that since it is more probable for blue light to get reflected with particles in air, they are scattered most? Why doesn't light get transmitted through rather than getting reflected(or scattered)? – Kartik Sharma Feb 7 '17 at 10:46
• The underlying level of light is the quantum superposition of photons. Yes, the scattering crossection plays a role on the color/frequencies built up or absorbed. If you want to see how quantum field theory builds the classical wave look at this blog entry by Motl, though it needs the math of quantum field theory, motls.blogspot.com/2011/11/… – anna v Feb 7 '17 at 11:41

As I understand it the process of 'scattering' is any series of reflections and refractions such that the energy that was once condensed such that it would 'hit' a small area will now 'hit' a larger area.