In 1922, Otto Stern and Walther Gerlach, two German physicists, conducted a groundbreaking experiment that demonstrated that electron spin and magnetism were related. To understand it, let’s imagine you have a strong magnet and a bunch of tiny beads. If you throw the non-magnetic beads through the magnet, you might think they’d just keep moving straight ahead, right?

But here’s the surprise! In the Stern-Gerlach experiment, when scientists sent silver atoms (instead of beads) through a magnetic field, they didn’t just go straight. Instead, they split into two paths! Some went up, and some went down — like two teams forming.

Why did this happen? In 1925, Uhlenbeck and Goudsmit, two Dutch physicists, explained this strange behavior. They figured out that each electron acts like a teeny magnet with its own “north” and “south” poles. Even more amazing, these tiny magnets didn’t point in every direction like you might expect. They only had two options: up or down. This was a big surprise!

They figured out that electron spin is an intrinsic magnetic moment, which is very different from the intrinsic angular momentum, which we discussed in the article Electron's spin - Part 1.

Otto Stern was awarded the Nobel Prize in Physics in 1943. Unfortunately, Walther Gerlach was not included in the award, but his role in the discovery of electron spin is highly respected and remembered in physics. George Uhlenbeck and Samuel Goudsmit did not win a Nobel Prize, but their work became a cornerstone of quantum physics.