In Tenet (2020), Laura speaks about inverted bullets:
Laura: It's inverted. Its entropy runs backward. So, to our eyes, its movement is reversed. We think it's a type of inverse radiation triggered by nuclear fission.
How entropy (thermodynamics) related to time flow?
Strictly speaking, thermodynamic entropy is not function of time, but function of thermodynamic state. 2nd law implies only that when adiabatic system goes from equilibrium state 1 to equilibrium state 2, thermodynamic entropy of state 2 cannot be lower than thermodynamic entropy of state 1.
We can introduce more definition of entropy for non-equilibrium processes that is consistent with the previous one for equilibrium states and then 2nd law implies(with caveats) that such entropy cannot sustainably decrease in time, it can only fluctuate - it can spontaneously decrease by small amount for a small time with small probability.
Measuring time flow by entropy increase is a very inaccurate and pointless thing to do. Mechanical or electronic clocks are much better.
