In T.H. White’s fantasy novel The Once and Future King, Merlyn the magician suffers from a rare and incurable condition: He experiences time in reverse. He knows what will happen, he laments, but not what has happened. “I have to live backwards from in front, while surrounded by a lot of people living forwards from behind,” he explains to a justifiably confused companion.
While Merlyn is fictional, the backward flow of time should not be. As the society of ants in White’s novel proclaimed, “everything not forbidden is compulsory,” and the laws of physics do not forbid time to run backward. For nearly 140 years, scientists have tried to rule out the backward flow of time by way of nature’s preference for disorder.
A new paper offers a solution. The secret ingredient, the authors say, is gravity. Using a simple simulation of gravitationally interacting particles, the researchers show that an orderly universe should always arise naturally at one point in time. From there, the universe branches in opposing temporal directions. Within each branch, time flows toward increasing disorder, essentially creating two futures that share one past. “It’s the only clear, simple idea that’s been put forward to explain the basis of the arrow of time,” says physicist Julian Barbour, a coauthor of the study published last October in Physical Review Letters.
Barbour, Koslowski and Mercati did not just toss in some particles and press play. Assuming a forward flow of time would have defeated the purpose of the exercise. Instead, they let the simulation rip and recorded a series of snapshots, like frames in a movie. Each frame captured the positions of the particles and recorded the system’s complexity — a measure that quantified the spread and clustering of the particles. (For the most part, complexity increases along with entropy.) Then the researchers pieced together the frames to create a coherent motion picture, much like someone ordering stills from a video that captures the motion of a swinging pendulum. After running the simulation many times with varying numbers of particles, Barbour and colleagues noticed an unmistakable pattern. At some instant during each simulation, all the particles would clump together into a homogeneous ball, a moment of minimum complexity. Then the complexity would increase. As the elapsed time from the instant of minimum complexity increased in either direction of time, so did the number of clumps and the distances between them. (1)
This could be the “solution”.
But for me the main problem arises from the fact that we want to create the problem. Why should there be an issue of how time flows? Why should we try to connect unconnected dots?
Stay in the present.
It is all there is.