Very interesting read here (for me, anyway):
http://www.livescience.com/48990-time-always-marches-forward-why.html?adbid=10152411275496761&adbpl=fb&adbpr=30478646760&cmpid=514627_20141204_36658417
Why Time Can't Go Backward: Physicists Explain
By Ian O'Neill, Discovery News | December 03, 2014 01:46pm ET
“Time is what keeps everything from happening at once,” wrote Ray Cummings in his 1922 science fiction novel “The Girl in the Golden Atom,” which sums up time’s function quite nicely. But how does time stop everything from happening at once? What mechanism drives time forward, but not backward?
In a recent study published in the journal Physical Review Letters, a group of theoretical physicists re-investigate the “Arrow of Time” — a concept that describes the relentless forward march of time — and highlight a different way of looking at how time manifests itself over universal scales.
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Traditionally, time is described by the “past hypothesis” that assumes that any given system begins in a low entropy state and then, driven by thermodynamics, its entropy increases. In a nutshell: The past is low entropy and the future is high entropy, a concept known as thermodynamic time asymmetry.
In our everyday experience, we can find many examples of increasing entropy, such as a gas filling a room or an ice cube melting. In these examples, an irreversible increase in entropy (and therefore disorder) is observed.
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As the Universe matures, he added, the subsystems become isolated enough so that other forces set up the conditions for the ‘classical’ arrow of time to dominate in low-entropy subsystems. In these subsystems, such as daily life on Earth, entropy can take over, creating a “thermodynamical arrow of time.”
Over Universal scales, our perception of time is driven by the continuous growth of complexity, but in these subsystems, entropy dominates.
“The universe is a structure whose complexity is growing,” said Mercati in a PI press release. “The universe is made up of big galaxies separated by vast voids. In the distant past, they were more clumped together. Our conjecture is that our perception of time is the result of a law that determines an irreversible growth of complexity.”
The next step in this research would be to look for observational evidence, something Mercati and his team are working on. “…we don’t know yet whether there is any (observational) support, but we know what kind of experiments have a chance of testing our idea. These are cosmological observations.”
For now, he hasn’t revealed what kinds of cosmological observations will be investigated, only that they will detailed in an upcoming, and likely fascinating, paper.