Sean Carroll

I know that some of you have heard about quantum mechanics a lot.

Some of you might be new.

This might be the first ever Mindscape podcast that you've listened to, which is great.

and if that's true let me tell you about this thing called quantum mechanics very very briefly because it could be ours all by itself the idea is back in the early part of the 20th century we knew about things like electrons you know electrons are always the example that physicists use because they're the elementary particle that is heavy enough and electrically charged enough to be manipulated

but also light enough to be pushed around very easily.

Like all of chemistry and much of material science is based on what electrons do.

There's also protons and neutrons in the nuclei of atoms, but they mostly sit there until you start considering nuclear fission or fusion or radioactivity or whatever.

But in your body and in the table in front of you, most of your nuclei are just sitting there going along for the ride,

while the electrons do the interesting work.

So anyway, electrons were understood in the early 20th century, but they had this funny property that we have a picture that you've all seen of an atom that looks like a little solar system, right?

With the nucleus in the center and the electrons orbiting.

But it was instantly realized that that can't be right because those electrons would give off light, lose energy, and spiral into the center of the nucleus.

But they don't.

In fact, atoms are pretty stable, matter is stable.

Our continued existence in the universe is evidence of that.

Now, how could you explain that?

And people came up with rather ad hoc ideas, like Niels Bohr just suggested that the possible orbits were just a discrete set.

Not every possible way that the electron could circle the nucleus was allowed.

Only some of them were allowed.

But it was not understood why that would be the case.