All the elementary entities of quantum mechanics spin but matter only half spins. Spinning an object once in our space returns its original state but doing the same to an electron only half-turns it. It is said to half spin because it takes two turns to return it to its original state, and quarks are the same.
Yet if an electron is a dimensionless point, it shouldn’t spin at all, so particle physics gave up trying to understand how it does:
“We simply have to give up the idea that we can model an electron’s structure at all. How can something with no size have mass? How can something with no structure have spin?” (Oerter, 2006), p95.
However in this model, an electron is a point particle with a photon structure. To us, a photon is a ray in one dimension, but quantum theory lets it vibrate into a dimension outside space, so it has a two-dimensional structure, like a piece of paper that can spin on its movement axis (Note 1). A photon has one dimension in our space but in quantum space it has two, like a piece of paper, so its spin is one not half. The four dimensions of quantum space also let photons vibrate in directions at right angles to each other (Note 2), so a filter that blocks horizontally polarized light doesn’t block vertically polarized light (3.7.2).
Why then do electrons half spin? The photons of an electron fill the channels of an axis to vibrate in different directions at right angles, so only half of them will be visible for a line of view, as the others, like thin paper sheets, will be invisible edge-on. If one photon is 100% visible, another at right angles will be 0%, for one that projects 99%, another will project only 1%, and so on.
In our space, one rotation returns an object to its original state because it needs an axis and two dimensions to rotate, which adds up to three dimensions. But for electrons in four-dimensional quantum space, one rotation only turns half its photons, and another is needed to turn the other half. It takes two of our rotations to return them to their original state, so electrons only half spin in our terms, and all matter entities are the same.
Note 1. For a photon moving in direction X, its quantum amplitude Q vibrates in plane QX, so the structure QX can spin.
Note 2. The orthogonal directions X, Y, Z of space give three orthogonal planes XY, YZ and XZ. A fourth dimension Q adds three more orthogonal planes Q1X, Q2Y, Q2Z, where Q1, Q2 and Q3 are at right angles.