Stephen Wolfram

You know, it wasn't until the beginning of the 20th century that Brownian motion was the final giveaway.

Brownian motion is, you know, you look under a microscope at these little pieces from pollen grains, you see they're being discreetly kicked, and those kicks are water molecules hitting them, and they're discreet.

And in fact, it was really quite interesting history.

I mean, Boltzmann had worked out how things could be discreet

and have basically invented something like quantum theory in the 1860s.

But he just thought it wasn't really the way it worked.

And then just a piece of physics history, because I think it's kind of interesting.

In 1900, this guy called Max Planck

who'd been a longtime thermodynamics person who was trying to, everybody was trying to prove the second law of thermodynamics, including Max Planck.

And Max Planck believed that radiation, like electromagnetic radiation, somehow the interaction of that with matter was going to prove the second law of thermodynamics.

But he had these experiments that people had done on blackbody radiation, and there were these curves, and you couldn't fit the curve based on his idea for how radiation interacted with matter.

Those curves, you couldn't figure out how to fit those curves.

Except he noticed that if he just did what Boltzmann had done and assumed that electromagnetic radiation was discrete,

could fit the curves.

He said, but this just happens to work this way.

Then Einstein came along and said, well, by the way, the electromagnetic field might actually be discrete.

It might be made of photons.

And then that explains how this all works.

In 1905, that was how that piece of quantum mechanics got started.

Kind of interesting piece of history.