 Many solutions to this problem have been proposed. Generally speaking, there are two ways to solve the problem: eliminate transitions of type  (2)  either with special boundary conditions or with laws of nature. The former method works if we assume that earlier states of the universe are of comparatively low-entropy and that (relatively) later states are not also low-entropy states. There are no high-to-low-entropy processes simply because earlier entropy was very low. Alternatively, the latter method works if we can somehow restrict the domain of physically possible worlds to those admitting only low-to-high transitions. The laws of nature are the straightjacket on what we deem physically possible. Since we need to eliminate transitions of type  (2)  while keeping those of type  (1)  (or vice versa), a necessary condition of the laws doing this job is that they be time reversal noninvariant. Our choice of strategy boils down to either assuming temporally asymmetric boundary conditions or of adding (or changing to or restricting to) time reversal noninvariant laws of nature that make entropy increase likely. Many approaches to this problem have thought to avoid this dilemma, but a little analysis of any proposed “third way” arguably proves this to be false.