Last year, physicist-poet Morris discoursed with admirable sobriety on The End of the World; here, he takes a cool, calm view of theories on the fate of the universe--even those so bizarre as to border on the outrageous. In the past, he notes, experts stayed with simple scenarios. The universe is either open or closed. If open, then the galaxies expand forever, and in due course light, gas, stars, will fade in the vicinity of a long-gone Earth. If the universe is closed, then gravity sooner or later will bring matter back together again, and whatever is not vacuumed up by black holes or annihilated by particle collisions will come together in the ""big crunch""--the obverse of the original big bang. To ask what happened before or after the big bang invites a third speculation--the oscillating universe. And this is where the simple scenarios become embellished by ever more baroque constructions. We learn that an oscillating universe might, so to speak, bounce higher and higher at each turn. On the other hand, the laws of nature might be re-processed (says Princeton's John Wheeler) at each go-round. Or, mini-black holes might be seeds that grow to become whole universes--or back again. Chances of resolving the issues are possible, of course. The Eighties may decide whether the neutrino has mass or not. Definitive evidence of a black hole may show up. Other issues may prove to be ""undecidable."" All these complexities Morris explains to the lay reader patiently and sensitively. And this--unlike the end of the world--is not ground that has been much worked over before.