Why does time always seem to move forward? This eternal mystery has puzzled physicists for more than a century, and they’ve offered several theories to explain time’s forward-moving arrow. The latest and most mind-bending speculation is that ‘while time moves forward in our universe, it may run backward in another, mirror universe that was created on the “other side” of the Big Bang’.
There are two leading theories that attempt to explain the direction of time by way of the relatively uniform conditions of the Big Bang. At the very beginning, the fledgling universe was extremely hot everywhere, so hot that even matter couldn’t exist. It was like a big superheated soup. But as the universe expanded out, it started cooling down forming stars, galaxies, planets, and other celestial bodies, birthing the present irregular structure of the universe and raising its levels of entropy.
The first theory proposed by Sean Carroll presently a professor at Caltech, and Jennifer Chen, his graduate student in 2004, proposes that time moves forward because of the contrast in entropy between then and now, with a distinction on the fact that the future universe will be much more disordered than in the past. This movement trend towards high entropy gives time its direction.
The latest theory by Julian Barbour from the University of Oxford suggests that a low entropy level in the early universe is inevitable due to forces of gravity, and eventually that’s what gives time its arrow. To test this idea, the theory’s advocates assembled a simple model with over 1,000 particles and the physics of Newtonian gravity. Lee Billings from the Scientific American explains:
The system’s complexity is at its lowest when all the particles come together in a densely packed cloud, a state of minimum size and maximum uniformity roughly analogous to the big bang. The team’s analysis showed that essentially every configuration of particles, regardless of their number and scale, would evolve into this low-complexity state. Thus, the sheer force of gravity sets the stage for the system’s expansion and the origin of time’s arrow, all without any delicate fine-tuning to first establish a low-entropy initial condition.
But there is a twist. The expansion that occurred after the simulated Big Bang didn’t just take place in one direction, but two. The basic Big Bang they modeled produced two universes, second one possibly a mirror of the first one. In the first universe, time appears to move forward while in the mirror one, time seemingly moved backward, at least from our perspective.
Billings interviewed the lead author of the new theory, Julian Barbour from the University of Oxford:
“If they were complicated enough, both sides could sustain observers who would perceive time going in opposite directions. Any intelligent beings there would define their arrow of time as moving away from this central state. They would think we now live in their deepest past.”
If this idea is correct, there is a possibility that George Lucas’s Star Wars didn’t take place a long time ago in a galaxy far, far away, but in the far future of our mirror universe.