Applying the principles of classical physics to this experiment, we can establish a link between the relative likelihood of the forward versus reverse path and the total entropy increase along the forward path. This symmetry relation arises from the time reversal property of Newton's laws.

This symmetry tells us that the larger the total entropy increase on the forward path, the more likely the forward path relative to the corresponding reverse path. For example, suppose the total entropy increase along the forward path is one. Then the symmetry states that the forward path is about three times as likely as the reverse path. What does this mean for the experiments? Suppose we performed the forward pulling and the reverse pushing experiments a very large number of times. If we observe the reverse path one thousand times, then the symmetry implies we will observe the forward path two thousand seven hundred eighteen times. If, however, the entropy increase is twenty instead of one, then we would need to see the forward path a billion times to expect to see the reverse path twice.