The Science Alert Article http://www.sciencealert.com/new-theory-suggests-that-two-parallel-universes-were-produced-by-the-big-bang presents a rather trippy theory: The explanation of the low entropy start state of our universe is explained by spontaneous ordering of particles through gravity! Here’s the central part:
Their model suggests that the Universe doesn’t need a special, low-entropy initial state in order for it to define an arrow of time - instead, the flow of time is just the inevitable result of gravity.
They came to this conclusion after studying a very simple model of our Universe comprised of just 1,000 particles. Using computer simulations, they tested how these particles interacted under nothing but the influence of the laws of Newtonian gravity.
What they found was that, no matter how the system was originally arranged, the particles would all eventually end up in these tightly packed, low-complexity states without any tinkering, simply through the sheer force of gravity.
This means that in order to set the direction of time’s arrow, we don’t need any perfect low-entropy conditions, we just need gravity.
But perhaps most interesting is what happened next in their model. From that highly condensed place, the system expanded outwards - but in two separate directions, each with their own time arrow travelling in a different direction.
Time running in two different directions is also a key theme in Greg Egan’s Orthogonal book trilogy. Once you have read that series, this theory doesn’t sound as implausible any more!
But I’m still sceptic about Newtonian gravity creating an emergent arrow of time. I mean, wouldn’t that mean that gravity can violate the second law of thermodynamics? If that’s actually true, we would need to rethink that law pretty deeply! Or is the theory above simply flawed?