Time in Quantum Mechanics

In this chapter, I discuss time in nonrelativistic quantum theories. Within an instrumentalist theory like von Neumann’s axiomatic quantum mechanics, I focus on the meaning of time as an observable quantity, on the idea of time quantization, and whether the wavefunction collapse suggests that there is a preferred temporal direction. I explore this last issue within realist quantum theories as well, focusing on time reversal symmetry, and I analyze whether some theories are more hospitable for time travel than others.