= Wave-particle duality
{wiki}
The history of light if funny.
First people thought it was a particle, as per <corpuscular theory of light>, notably <Newton supported the corpuscular theory of light>.
But then evidence of the <diffraction> of light start to become unbearably strong, culminating in the <Arago spot>.
And finally it was undertood from <Maxwell's equations> that light is a form of <electromagnetic radiation>, as its speed was perfectly predicted by the theory.
But then evidence of particle nature started to surface once again with the <photoelectric effect>. Physicists must have been driven mad by all these changes.