This is a running list of corrections to things I thought I knew at one time but which have either proven to be untrue or at least been called into question.

• Schrödinger did not claim that quantum mechanics says that a cat can be both alive and dead at the same time. (Schrödinger’s cat is a reductio ad absurdum.)
• Photons are not particles.
• Spacetime may not be curved.
• Wormholes may not exist (spacetime may be simply connected).
• ‘Hidden variable’ theories are possible. (von Neumann was wrong, Feynman was wrong because he believed von Neumann).
• Particles in quantum mechanics do not travel in straight lines, even in the absence of external forces.
• Mathematics is not hierarchical except by how it is taught. (You don’t need to know trig to learn calculus.)
• A rotation through 360° does not return an object in physical 3D space to the same point. A rotation through 720° does.
• Pauli spin matrices do not arise from quantum mechanics. (They are a matrix representation of quaternions which are perfectly good classical mechanics.)
• Dirac matrices do not arise from quantum mechanics and specifically are not unique to the Dirac equation. (They are a matrix representation of rotations in 4-dimensional space and are perfectly good relativistic mechanics.)
• Linear algebra is not the same thing as matrix algebra.