Homer nodded: von Neumann's surprising oversight

Understand

We review the famous no-hidden-variables theorem in John von Neumann's 1932 book on the mathematical foundations of quantum mechanics.

• We describe the notorious gap in von Neumann's argument, pointed out by Grete Hermann in 1935 and, more famously, by John Bell in 1966.
• We disagree with recent papers claiming that Hermann and Bell failed to understand what von Neumann was actually doing.