(ORDO NEWS) — Two separate groups of physicists who studied the passage of time in the Universe suggested that about 14 billion years ago, the Big Bang could give rise to a second, inverse “mirror Universe,” where time moves in the opposite direction.
In fact, if we looked at the mirror universe, we would see how time moves from the future to the past, but from the point of view of that universe, it would look like our time is moving backward rather than forward, the researchers suggest.
“Time no longer exists,” said Olivia Goldhill, one of the physicists, Julian Barbour of Oxford University in the UK. “The direction and course of time we must determine from what is happening in the universe. When we look at time in this way, it’s natural to say that time begins at a central point and moves in opposite directions.”
Physicists have struggled for decades to ensure that not one of the fundamental laws of physics governing the universe requires time to move forward. “Whether it is Newton’s gravity, Maxwell’s electrodynamics, Einstein’s special and general theory of relativity, or quantum mechanics, all the equations that best describe our universe work great if time goes forward or backward,” Lee Billings writes for Scientific American.
Back in 1927, the British astrophysicist Arthur Eddington suggested that there is an “arrow of time” that acts as a fundamental property of the branch of physics called thermodynamics.
The second law of thermodynamics states that in any isolated system, such as the Universe, entropy (or disorder) should increase, therefore, regardless of whether the time arrow moves back or forward, matter should always tend to a higher state of entropy.
Our version of the Universe and its thermodynamic arrow of time is such that when the Big Bang occurred, the Universe arose as a whole egg with a high order and low entropy. Soon, this “egg” was broken, and matter went into a chaotic state with high entropy.
The problem with this assumption is that it does not take into account the reverse motion of time, which is allowed by the fundamental laws of physics. You cannot move from a broken egg to a highly ordered, perfectly whole egg, so what does it give?
Joshua Falcon explains for the New Scientist:
“By reducing the scale of the entire Universe, we … define the future as the direction of time in which entropy increases. By studying the movement of distant galaxies, we can predict how space will develop. Or we can rewind time back to the Big Bang, when the Universe should have had much less entropy.
Try to rewind time even further and we will meet with the cosmological mystery. We cannot continue if the Big Bang really was the beginning of time, but then, why did it have such low entropy? And if this were not the beginning of time … we still would like to know how the Universe could reach such a state with low entropy that would allow the arrow of time to form.”
Julian Barbour and his UK counterparts published their article back in 2014, arguing that this arrow of time is determined by gravity, not thermodynamics. In a publication for Physical Review Letters, they describe a computer simulation of 1000 particles, all of which were controlled by Newtonian gravity – the simplest simulation of the universe you can imagine.
They found that due to gravity, the particles were at the smallest distance from each other, which they called the Janus point. Then the particles began to scatter in different directions, showing how time can move back and forth in the real multiverse.
“When particles expand, they do it in two different time directions,” Goldhill writes. “Barbour and his colleagues created a simplified model of the Universe, consisting of 1000 particles, showing this double expansion with a gravitational structure in both directions.”
“This is the simplest,” says Barbour about his research. “You start from the central point of Janus where the movement is chaotic – it looks like the Greek concept of primary chaos – but then a structure is formed in both directions. If the theory is true, then there is another Universe on the other side of the Big Bang, in which the direction of time is opposite to ours.”
Two other physicists, Sean Carroll of the California Institute of Technology and Alan Guth of the Massachusetts Institute of Technology (MIT), came up with similar results using a different particle model.
In their model, they created a finite cloud of particles and placed it in an infinite Universe. Soon enough, two different time arrows appeared spontaneously – half of them move towards increasing entropy, while the other half thickens in the center, decreasing entropy before passing through it and returning to chaos.
Perhaps the middle region of low entropy describes the Big Bang, and also solves the problem of the absence of a “beginning of time” – the lowest state of chaos.
Carroll and Gut have not yet published the results of their model and acknowledge that there are many limitations that still need to be addressed.
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