In our earlier discussion on quantum mechanics, we explored the strange idea that nature might be fundamentally random like “the ghost in the atom” (read here). Today, we turn to another deep and long-standing mystery at the heart of quantum physics: the true nature of light.

For centuries, scientists studied light through the lens of geometry. Simple phenomena like reflection and refraction could be neatly explained by treating light as a collection of straight lines, or rays.

If a beam of light hits a mirror, it bounces off at an equal angle — a rule so straightforward that it became the foundation of ray optics. For a long time, this model seemed sufficient. It described how light travels, bends, and reflects with remarkable precision.

But as experiments became more sophisticated, cracks began to appear in the ray model. The most famous challenge came from the double-slit experiment — an experiment so simple in design, yet so profound in its implications.

Imagine shining light through two narrow slits and observing what appears on a screen behind them. If light consisted of tiny particles, we’d expect two bright spots — one behind each slit. As shown in the figure below.