Diffraction
The bending and spreading of waves around obstacles or through narrow openings. It is most pronounced when the obstacle or opening is comparable in size to the wavelength.
In 1818, Siméon Denis Poisson argued that if light were a wave, a bright spot should appear at the center of a circular object's shadow — which he thought was absurd. But when Arago actually ran the experiment, the bright spot appeared, proving light's wave nature.
0