Why is light reflected?

Question

okay so light is reflected from an object into our eyes. but why is it reflected in the first place?

Answer 1

Light is energy.  It MUST "go somewhere", since it cannot simply vanish.  The two possibilities are that it is absorbed by what it hits, or that it bounces off of what it hits and comes back at you and you see it (in the case of visible wavelengths), feel it as heat (in the case of longer wavelengths), or experience it as sunburn (in the case of shorter wavelengths).  The "why" of reflection depends on the molecular or atomic composition of the material at the surface of the thing being struck by the light...  Think of a pool of water covered in floating ping-pong balls; if you make waves of different sizes at the edge of the pool, the tiniest ripples will bounce of the balls and come back to you, ripples of just the right height will be absorbed (making the balls jump up and down), and bigger ripples will just make the balls float over the top...

The same thing happens when light energy hits an atom or a molecule!

Answer 2

Any theory of light must be able to account for the phenomenon of reflection.

Newton thought that light are particles - precisely because such a theory helps to explain why light reflects. When a ball hit a wall, it will bounce back. Similarly, light particles will "bounce" back after hitting the wall.

However, this theory is inadequate and makes wrong predictions about light, especially when it comes to refraction.

Huygen's principle is perhaps the best classical (i.e. pre-quantum physics) explanation as to why light reflects. It simplify states that all points of a wave front of light in a vacuum or transparent medium may be regarded as new sources of wavelets that expand in every direction at a rate depending on their velocities. This predicts correctly that the angle of reflection will be the same as the angle of incidence.

See the applet:

http://www.walter-fendt.de/ph14e/huygens...

The most complete explanation of why light reflects require an understanding of Quantum Electrodynamics which is probably out of the scope of our discussion