Janus, Vatican museum, photo by Loudon Dodd
We can always count on FQXi member Julian Barbour to raise the tone of the conversation, this time by referencing the Roman two-faced god Janus with his new theory that explains the origin of time's arrow, using gravity (Phys. Rev. Letts, 113, 181101).
I've just opened a thread on for discussing our latest podcast (29 November 2014), but I neglected to open one for the previous podcast, which featured an interview with Barbour and his colleague Flavio Mercati, who spoke about their new model. According to them, the big bang gave rise to two back-to-back "Janus universes," with arrows of time that run in opposite directions. Their model also runs counter to the usual conception in which the arrow of time tracks *increasing* entropy in the universe; they argue instead that as time progresses, the universe's entropy *decreases*.
Since that podcast interview was posted in October, Barbour's model has been gaining interest. The APS highlighted the work with a Viewpoint piece, in which Steven Carlip provides commentary on the paper, describing mysteries about the arrow of time that must still be addressed (such as why the arrows that arise from different physical phenomena, not just gravity, all point in the same direction).
Bob Yirka at phys.org has also written an accessible account of the team's research.
So, if you haven't already, please do go back and listen to Barbour's interview with us, from October.
What do you think? Is this enough to solve the problem of the origin of time's arrow?
In the same edition you can hear another expert on the physics of time, Paul Davies, talking about something quite different: his atavistic model for cancer, which he likens to a cell's "safe mode" that's triggered when the cell faces an environmental threat and reboots itself. For more on this topic, you can also see a news item that I wrote for Scientific American: "Did Cancer Evolve to Protect Us?"
Physical Review Letters