Max Planck

Max Planck (1858–1947) was a careful, conservative German physicist who — almost against his own wishes — kicked open the door to quantum theory. He discovered that energy comes in tiny indivisible packets, and physics was never the same again.

The big idea

To explain the colours of a glowing hot object, Planck had to assume light energy comes in discrete lumps, each carrying an amount set by his famous constant. That single desperate guess is the seed of the photoelectric effect and, ultimately, of wave–particle duality — the strange idea that light is both a wave and a stream of particles. Planck's constant now sits inside nearly every equation of the quantum world.

Here's the twist: Planck hated his own discovery. He was a traditionalist who called the energy packets "an act of desperation," a mathematical trick he hoped someone would soon explain away. Instead, Einstein and others showed the packets were real, and Planck had accidentally founded quantum physics. His later life was marked by deep personal tragedy, yet he kept working and speaking out for science through Germany's darkest years, and the country's largest research organisation still proudly bears his name.