At the quantum level, there are events that *distinguish* the past from the future, such as the collapse of the wave function, which makes the past and future around a measurement asymmetrical, and thus represent an irreversible change (or rather, a change that removes the reversibility of the system being observed).

This forces us to treat time as continuous, with any given interval of time being divisible, whereas QM implies that time is quantized (or quantizable), creating conflict between the time of mathematics and physical theory (which relies on mathematics to get it's point across).