Caltech physicist Sean M. Carroll has been wrestling with the mystery of time. Most physical laws work equally well going backward or forward, yet time flows only in one direction. Writing in this month’s Scientific American, Carroll suggests that entropy, the tendency of physical systems to become more disordered over time, plays a crucial role. Carroll sat down recently at Caltech to explain his theory.

Welcome to my parallel universe page. In this universe, I've published two articles reviewing the subject: a shorter one in Scientific American (May 2003 issue) and a longer and slightly more technical one in astro-ph/0302131, in the book Science and Ultimate Reality: From Quantum to Cosmos, honoring John Wheeler's 90th birthday (J. D. Barrow, P.C.W. Davies, & C.L. Harper eds. Cambridge University Press 2003).

Unconventional cosmologist Max Tegmark says mathematical formulas create reality.

This fall, NASA and the Department of Energy plan to invite proposals for a $600 million satellite mission devoted to dark energy. But some scientists fear that might not be enough. When astronomers and physicists gathered at the Space Telescope Science Institute recently to take stock of the revolution, their despair of getting to the bottom of the dark energy mystery anytime soon, if ever, was palpable, even as they anticipate a flood of new data from the sky in coming years.

Welcome to what physicists call the Boltzmann brain problem, named after the 19th-century Austrian physicist Ludwig Boltzmann, who suggested the mechanism by which such fluctuations could happen in a gas or in the universe. Cosmologists also refer to them as “freaky observers,” in contrast to regular or “ordered” observers of the cosmos like ourselves. Cosmologists are desperate to eliminate these freaks from their theories, but so far they can’t even agree on how or even on whether they are making any progress.

One of the most basic facts of life is that the future looks different from the past. But on a grand cosmological scale, they may look the same

a different cosmology .... one based on electrics rather than gravity