Time is quixotic: the idea of it is fundamentally interesting because, on the surface, it's a man-made construction--calendars, clocks, time zones--designed for convenience, to enable a sophisticated working society to function. And, like most fundamental ideas, "time" is based on astronomy (the position and rotation of the earth around the sun) which in itself is, like our existence, a happy accidental byproduct of the formation of the universe. (An added quirk here is that, from a human perspective, space is time--the universe is so vast that light reaching us today is millions of years old.) So, does time really exist in the sense that the present is different from the past or future, or is it an illusion?
I suspect the latter, that "the past is present memory," to quote St. Augustine. According to Sean Carroll, a physicist at CIT, this places me squarely among the "presentists," a group championed by Julian Barbour and his seminal work The End of Time: The Next Revolution in Physics. However, Carroll recently wrote a paper arguing that "the universe is described by a quantum state obeying ordinary time-dependent quantum mechanics," and earned a second-place finish in the Foundational Questions Institute's essay contest for his trouble (it's worth noting, though, that Barbour's entry placed first). Titled "What if Time really Exists?" (itself a nod at the scientific community's reluctance to incorporate it) his essay raises some interesting questions. For example: Schrodinger's deterministic wave equation posits that knowledge of the state of a system at any one time is sufficient to determine its future and past evolution in time; however, "what if time exists, and is eternal, and the state of the universe evolves with time obeying something like Schrodinger's equation?" Thanks to string theory, physicists can attempt to answer this question by interpreting certain implications of quantum gravity, namely, duality. Duality brings us back to Susskind's Holographic Principle, a concept that has its applications with time: if quantum gravity in ten dimensions is equivalent to ordinary quantum field theory in four dimensions, as demonstrated by Juan Malcadena's gauge/gravity duality, then there should exist a description of the universe "consisting simply of a quantum-mechanical state evolving with time." Right?
What remains to be reconciled is that quantum mechanics operates under the assumption that time is infinite in all directions, but, as it related to entropy, "within our observable universe, time has an arrow," meaning that time is irreversable. The catch is that within the Schrodinger equation, quantum time evolution is information-preserving, meaning "we can reliably reconstruct the past just as well as the future." Obviously, to any observer living in the last four hundred million years, this just isn't applicable (unless LaToya Jackson really does know something we don't). But, the idea remains that as time marches on, it doesn't morph into the future, the future was already there: I sit here typing, and now I'm typing again, and suddenly the future is the present, ad infinitum. Free will makes this concept more complex, but doesn't negate it; mortality makes it more philosophical, but not mystical.
Carroll concludes by saying that because entropy can grow into the future and into the past, "the very far past of our universe could be experiencing an arrow of time directed in the opposite sense to our own." In an infinite-dimenstion Hilbert space, that seems to throw a lot of cold water on creationism, to say the least. But it does make for interesting fodder where thought and consciousness is concerned, because it implies that everything, ever, still exists and (theoretically) could be accessed. Move over, SAP!
Carroll also has a book coming out this year: From Eternity to Here: The Quest for the Ultimate Theory of Time.