# Why is diffraction a wave phenomenon?

Jul 21, 2015

Basically diffraction is the "invasion" of the space behind an obstacle by light shining on an aperture.

#### Explanation:

Light seems to be able to pass an aperture and propagate even into the space that is covered bi the walls of the aperture:

If you consider light as a shower of particle-like entities (photons) there is no classical reason why one of these "bends" its trajectory to pass into the shadow region behind the obstacle!

If, instead, you consider light as a wave you can consider Huygens construction of secondary waves where each point on a front of your wave (say a crest) becomes a source of secondary spherical waves whose envelope forms the next crest!!!

In the simple (but powerful) visual arrangement of Huygens Principle each point on a wavefront is source of spherical secondary spherical waves that will build the next wavefront...so a point near the edge of the aperture will generate a spherical wave that invades the area behind the obstacle!!!
The good thing about light is that when you need is a wave otherwise is particles...in general is a...Wavicle! :-)
Hope it helps!