We’re born, we get older and eventually die. That’s just how time works in our universe. But could there be a mirror universe out there where time runs backwards and everyone is essentially Benjamin Button? Surprisingly, the answer is apparently ‘yes’ – theoretically, at least.
According to Quartz and The Daily Star, scientists note that there are no laws of physics that say that time has to move in a forward direction. So what causes it to happen? Most physicists point towards continually-increasing entropy, the lack of order and predictability in the universe.
Yet two groups of scientists decided to take a closer look at the matter, and in both cases, their research came to the same conclusion – time appears to move in two different directions, which suggests that when the Big Bang created our universe, it also created a second, mirror universe where, from our perspective anyway, time would appear to be moving backwards.
Discovering the ‘Janus point’ that divides parallel universes
One of those studies, published last year in the journal Physical Review Letters, explained that Newton’s theory of gravity permits the conditions for time to move in a specific direction, and that for any confined system of particles (such as a self-contained universe), gravity attempts to minimize the distance between said particles.
When those particles expand outwards, they do so in two different directions – something that the authors of the study demonstrated using a simplified model of the universe. Ultimately, the way in which we experience time is based on increasing entropy. Essentially, the compared the flow of time to the point of a river where it splits and flows in opposite directions.
Speaking in terms of time, that point where time splits and flows in opposing directions has been dubbed the “Janus point” in honor of the two-headed Roman deity. According to the authors, if their theory is correct, another universe exists on the opposite side of the Big Bang, and there, the flow of time is the complete opposite of ours.
Even if such a time flow exists, however, they said that we would never be able to experience it. As study co-author Flavio Mercati from the Perimeter Institute for Theoretical Physics explained to Quartz, “We’re on one side of the Janus point. On one side you get your arrow of time and can never experience the other one. It’s in your past.”
‘The two-headed arrow of time’
Building upon that research, two other physicists – Sean Carroll from the California Institute of Technology in Pasadena and Alan Guth from Massachusetts Institute of Technology – have now developed a new, similar particle model that shows a pair of parallel universes where time flows in two opposite directions, according to New Scientist and The Daily Mail.
Like their predecessors, Carroll and Guth used entropy as the starting point for their model, and found that the direction in which time flows does not matter. To us, the future is the direction of time in which entropy increases, while entropy would be much lower in the past, they explained. While we believe one event ultimately leads to another, this is not necessarily the case.
The researchers developed a model in which they inserted a fixed number of particles, each with a randomly assigned velocity, into an infinite universe. Eventually, they said, arrows of time that flowed in a specific direction spontaneously developed. Half of the particles moved towards the center of the model, decreasing entropy, while the other half moved to the edges, increasing it.
Once the particles passed through the center, they continued on towards the edges, a concept the study authors refer to as the “two-headed arrow of time.” In short, if an arrow of time emerges in one direction, the same will happen in the opposite direction, regardless of its starting point. The model, they claim, reveals that particles all ultimately move outward, that entropy grows without limit and that the initial direction of the arrows is essentially irrelevant.
“The point that Alan and I are trying to make, is that it’s very natural in those circumstances that almost everywhere in the universe you get a noticeable arrow of time. Then of course, you do the work of making it realistic, making it look like our universe,” Carroll told New Scientist. While the model has yet to be published, he noted that it could be applicable to the multiverse.