Stern–Gerlach experiment
In: Physics
What Stern and Gerlach did was shot a stream of silver atoms through a magnetic field, and recorded where they hit a screen at the other end.
What they saw first was that the particles were deflected by the magnetic field, and therefore hit the target at different locations than “dead straight”. What this shows is that particles have angular momentum – that is, they act like they’re spinning. This phenomenon is called “spin”, even though the particle isn’t actually physically spinning. Because these silver particles have spin, the (changing) magnetic field pushes harder on one side than the other, so they curve.
The more important thing that they saw was that the particles were hitting in two distinct locations, instead of an even spread. You would expect that particles would be spinning by different amounts that were more-or-less random, and so they would be deflected by random amounts. What Stern-Gerlach showed was that spin values can only be distinct, separate numbers – they’re “quantized” to particular values. What we’ve since discovered is that _all_ particles will have spin of 0, 1/2, 1, 3/2, 2, 5/2, etc., based on a defined base number. From here on, there’s a _massive_ quantum physics rabbit hole, but the short version is that particles with whole-number spins behave a certain way, and particles with half-spins behave a different way.
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