Magnets

Its an interesting challenge to explain physics using twitter. Working with ideas than can be chopped up to 140 character chunks really focuses you. Magnets are complicated things, but this should give you an idea.

Apologies for the profanity. In retrospect they were unnecessary.

Magnets, how they fucking work:

A stationary charge generates an electric field.

— Matthew Buckley (@physicsmatt) July 4, 2016

Special relativity means that time and space change as objects move.

— Matthew Buckley (@physicsmatt) July 4, 2016

As a consequence, so that all observers to see similar effects (charges repelling or attracting) moving charges generate magnetic fields.

— Matthew Buckley (@physicsmatt) July 4, 2016

This is why Einstein's paper on special relativity is titled "On the Electrodynamics of Moving Bodies."

— Matthew Buckley (@physicsmatt) July 4, 2016

So the simplest magnet is just a charge moving in a circle. Or a current of charges moving in a circle...

— Matthew Buckley (@physicsmatt) July 4, 2016

Such current are, of course, a critical part in how we generate electrical power.

— Matthew Buckley (@physicsmatt) July 4, 2016

But, most people thinking of a "magnet" (and how they fucking work) are thinking of a piece of magnetized iron. How do they work?

— Matthew Buckley (@physicsmatt) July 4, 2016

An electron has electric charge. It also has "spin." that is, an electron in some sense rotates.

— Matthew Buckley (@physicsmatt) July 4, 2016

It is a point particle, so you can't think of an electron as a little charge running in a circle.

— Matthew Buckley (@physicsmatt) July 4, 2016

Nonetheless, because of it's spin and its charge, it has its own tiny magnetic field (almost exactly 2x as strong as non-QM would predict)

— Matthew Buckley (@physicsmatt) July 4, 2016

Atoms are full of electrons. In most materials, half the little electron "magnets" point in one direction, then other's opposite.

— Matthew Buckley (@physicsmatt) July 4, 2016

This is because electrons can't "double up" in their orbits of the atom. But opposite "spin" counts as a different orbital state.

— Matthew Buckley (@physicsmatt) July 4, 2016

This is because electrons can't "double up" in their orbits of the atom. But opposite "spin" counts as a different orbital state.

— Matthew Buckley (@physicsmatt) July 4, 2016

So, pretty naturally, atoms will have most of their electron "magnets" canceled out by other of their electrons.

— Matthew Buckley (@physicsmatt) July 4, 2016

However, in some materials, there is an unpaired electron. With nothing to cancel it's magnetic field.

— Matthew Buckley (@physicsmatt) July 4, 2016

Furthermore, in some of *those* materials, the orbits of those electrons are such that, when 2 atoms are placed near each other...

— Matthew Buckley (@physicsmatt) July 4, 2016

...the orbitals of the two unpaired electrons have room to "move apart" if the two atom's unpaired electrons point in the same direction.

— Matthew Buckley (@physicsmatt) July 4, 2016

That is, these materials find it preferable for nearby atoms to have all their little electron magnets aligned.

— Matthew Buckley (@physicsmatt) July 4, 2016

So these materials can get huge numbers of electrons all with their magnets pointing in the same direction. Result: a macroscopic field.

— Matthew Buckley (@physicsmatt) July 4, 2016

...and that's how ferromagnets work. And explains why iron is a ferromagnet but steel isn't

— Matthew Buckley (@physicsmatt) July 4, 2016

carbon-doped iron (steel) can change the shape of the iron atom's electron orbitals, preventing the cross-atom alignment.

— Matthew Buckley (@physicsmatt) July 4, 2016

So, to know how a magnet works, you only need special relativity, advanced QM, basic quantum field theory, and statistic mechanics.

— Matthew Buckley (@physicsmatt) July 4, 2016

I can't imagine why more people don't know how magnets fucking work.

— Matthew Buckley (@physicsmatt) July 4, 2016

but short of the magnetic field of a Kerr-Newman black hole, I can't think of any requirement for general relativity to understand magnets.

— Matthew Buckley (@physicsmatt) July 4, 2016