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There are a few things that everyone agrees on. The directionality that we observe in the macroscopic world is very real: Teacups shatter but do not spontaneously reassemble; eggs can be scrambled but not unscrambled. Entropy — a measure of the disorder in a system — always increases, a fact encoded in the second law of thermodynamics. As the Austrian physicist Ludwig Boltzmann understood in the 19th century, the second law explains why events are more likely to evolve in one direction rather than another. It accounts for the arrow of time.
But things get trickier when we step back and ask why we happen to live in a universe where such a law holds. “What Boltzmann truly explained is why the entropy of the universe will be larger tomorrow than it is today,” said Sean Carroll, a physicist at the California Institute of Technology, as we sat in a hotel bar after the second day of presentations. “But if that was all you knew, you’d also say that the entropy of the universe was probably larger yesterday than today — because all the underlying dynamics are completely symmetric with respect to time.” That is, if entropy is ultimately based on the underlying laws of the universe, and those laws are the same going forward and backward, then entropy is just as likely to increase going backward in time. But no one believes that entropy actually works that way. Scrambled eggs always come after whole eggs, never the other way around.
full: https://www.quantamagazine.org/20160719-time-and-cosmology/ _________________________________________________________ Full posting guidelines at: http://www.marxmail.org/sub.htm Set your options at: http://lists.csbs.utah.edu/options/marxism/archive%40mail-archive.com
