Quanta

Imagine a universe where everything can be broken down into tiny bits.

No, I’m not talking about atoms here, although that was an important first step in visualizing the universe I’m talking about.

In this universe, energy isn’t continuous, but instead made of tiny particles. Any time you see anything, tiny particles of light are delivered to your eye and into your brain for processing, itself made up of tiny particles that send other tiny particles around.

There’s a smallest amount of anything you can imagine, from time to distance itself, to every piece of energy or matter or anything. Anything.

It might not shock you to realize that this appears to be the way our universe works.

Isaac Newton suggested something that sounded pretty crazy at the time. He suggested that light was made up of tiny particles he called corpuscles.

This idea helped to explain a lot of things about light, like the way it bounced off of mirrors, or the way it seemed to slow down in a different medium (refraction). If you could imagine uncounted tiny particles flying through the air (or space), you could envision and predict a lot of the behavior of light.

Still, light seemed to act like a wave at times, too, and this way of looking at things explained more phenomena than Newton’s corpuscular theory, so the idea that light is made up of particles was kind of shelved for two centuries.

It was Newton’s successor and famous shoulder-stander, Einstein, who brought the idea of particles of light back into the scientific public eye in 1905, his miracle year of publishing papers that shocked the physics world. Einstein’s conclusions didn’t build on Newton’s work, exactly, though—it was Max Planck to whom the largest debt was owed.

Planck introduced the concept of quantized energy levels, suggesting that energy, like light, could only be emitted or absorbed in discrete quantities, which he called quanta. Planck himself may not have truly believed in quantization, but it solved a perplexing problem about blackbody radiation, and so it was useful to pretend as though it was real.

Einstein had a way of removing mental barriers from things he was considering, so he just took Planck’s idea literally and drew some conclusions as a result. We call Einstein’s light packets photons today. This is the smallest amount of light you can ever have.

Einstein’s work on the photoelectric effect, which directly built upon Planck's quantum theory, offered a new lens through which to view Newton’s corpuscles, bridging the gap between the particulate nature of light and its wave-like behaviors.

New ideas in physics almost always build upon older ideas, and this synthesis of concepts is really clear in the story of quantum mechanics. The old ideas live on in the new ones, having been modified and improved.