KentuckyFC writes: "One of the great theories of modern cosmology is that the universe began in a Big Bang. It's backed up by numerous lines of evidence, such as the cosmic microwave background and so on. But what caused the Big Bang, itself? For many years, cosmologists have fallen back on the idea that the universe formed spontaneously; that the Big Bang was result of quantum fluctuations in which the universe came into existence from nothing. But is this compatible with what we know about the Big Bang itself and the theories that describe it? Now cosmologists have come up with the first rigorous proof that the Big Bang could indeed have occurred spontaneously and produced the universe we see today. The proof is developed within a mathematical framework known as the Wheeler-DeWitt equation. Heisenberg's uncertainty principle allows a small region of empty space to come into existence probabilistically due to quantum fluctuations. Most of the time, such a bubble will collapse and disappear. The question these scientists address is whether a bubble could also expand exponentially to allow a universe to form in an irreversible way. Their proof (PDF) shows that this is indeed possible. There is an interesting corollary: the role of the cosmological constant is played by a property known as the quantum potential. This is a property introduced in the 20th century by the physicist David Bohm, which has the effect of making quantum mechanics deterministic while reproducing all of its predictions. It's an idea that has never caught on. Perhaps that will change now."