It's a testament to theoretical physics that the question of "what happened before the Big Bang?" no longer falls into the realm of nonsense. The key is to understand the colossal energies released 13 plus billion years ago, as Sean Carroll, CalTech theoretical physicist and author of "From Eternity to Here," explains in this piece from Alan Boyle, Dodging the Arrow of Time.
Sure, you can refreeze the water into an ice cube. Heck, it's theoretically possible to reprocess a scrambled egg, molecule by molecule, so that it looks like a raw egg again. But that requires adding more energy into the system. The total entropy of the system still goes up. It's the law - specifically, the Second Law of Thermodynamics.
Carroll's book [From Eternity to Here] isn't so much about the impossibility of time travel as it is about that bigger mystery of entropy. Why does the arrow of time fly in just one direction, and where did that arrow come from, anyway? Does it make sense to talk about what happened before the arrow flew?
Some physicists would say such questions can't be discussed in scientific terms. But Carroll isn't one of those physicists. After explaining in detail what we know about entropy and its relation to the arrow of time, he moves on to the more speculative side of the issue.
'Why do we ever find an egg?' Carroll asked me during our interview. 'It's because it's not an isolated system in the universe. ... We should think about the universe like we think about the egg, which is that it came from something else.'
Having tied increasing disorder - increasing entropy - to the arrow of time, Carroll explains in the Cosmic Log piece that the idea of a multiverse, where ours is but one of potentially many expansive histories, makes sense from the view of science.
Sean Carroll will be speaking at the IdeaFestival 2010 on cosmology and time. For a limited time only, "Insider Passes" are available to hear him - and many other creative and accomplished poeple - span a universe of ideas.
They just might give you one.
Image: "Tunnels of Time" by fdecomite