Reversing the direction of time doesn’t prevent the equations from working. That is, time could point either way and we wouldn’t be able to tell the future from the past. Yet we see a clear difference between the past and the future. This is ‘the second problem of physical time’. How do we reconcile the fact that our equations work just as well whichever way time is running with the irreversibility of time that we experience in the world? https://www.sciencefocus.com/science/the-closer-we-look-at-time-the-stranger-it-gets