There are other problems with this procedure. It requires us to specify the initial microstate. But it is usually impossible for us to know the exact microstate at any zero of time—a typical measurement tells us either about macroscopic averages over the entire state or the microscopic configuration of one small part of the system. Moreover, unavoidable interactions with the environment (molecules from the surrounding air collide with the tea cup) cause the microstate to change rapidly and unpredictably.