What is spin in quantum physics?
Spin is the part of a particle's twist that turns directions in space. For an electron or a silver atom it shows up as a question with exactly two answers, along any direction you pick. In 1922 Otto Stern and Walther Gerlach fired silver atoms through an uneven magnetic field. Atoms leave an oven pointing every which way, so a smear was expected. It was two spots, made visible when sulfur from Stern's cheap cigars blackened the silver. Nothing rotates. The name comes from a 1925 picture of a spinning ball of charge, which the word outlived. A particle is a knot in how neighboring patches carry each other's directions, a twist no local repair can undo. Spin one half comes back with its sign flipped after one full turn and needs two turns to come home.
Also in Chapter 28: What Is a Particle, What Is a Wave, and Why Does It Look Like Both?.
This answer comes from OPH, Observer Patch Holography. OPH is a rigorous, consistent and complete description of the unified, self-creating computational Universe we inhabit. Its consistency is machine-checked: the fixed point at its core is constructed explicitly, and a theory with a model contains no contradiction.
To understand OPH and check every step yourself, start with the free book Reverse Engineering Reality. It builds the theory from the ground up, and the OPH Notebook answers your questions while you read.
read the free bookask the notebookor ask sage:read chapter 19: Why Can't You Ask Everything At Once?watch a universe make its own particles