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It’s one of those things you think about at 2 a.m. after a Twilight Zone marathon. Is there such a thing as a mirror universe, and, if there is, what would we see in the mirror?
This goes beyond just a mirror universe — try an anti-universe. A new theory suggests the universe we live in has a sort of anti-universe running backwards in time, and it only gets weirder from there, because its existence could mean something floating around in this universe would make it possible to detect dark matter. That something is a subatomic particle known as a neutrino. What makes this particular (hypothetical) type of neutrino so intriguing is that it supposedly behaves like dark matter, and if it can be detected, minds will be blown.
The thought that actual experiments could determine the existence of matter we cannot see or feel seems unreal, but physicist Latham Boyle went there. There is a sort of symmetry in the universe that might mean there has to be an opposite mirror image. Boyle and his colleagues Kieran Finn and Neil Turok, of the Perimeter Institute for Theoretical Physics in Ontario, Canada, coauthored a study, recently published in Annals of Physics, which explains how that symmetry can be used to illuminate dark matter.
“In our theory, the Big Bang is a kind of exotic mirror,” he told SYFY WIRE. “In an ordinary mirror, it is as if the world on the other side has one of its spatial directions reversed, whereas with the Big Bang, it is as if the world on the other side has its time direction reversed.”
So time is turned on its head instead of space. This is what happens when you take the concept of CPT symmetry and go beyond just applying it to forces and fields and instead apply it to the entire universe. CPT symmetry stands for charge, parity (equality) and time reversal. When you reverse charge theoretically, you have antimatter instead of matter. Then you have time and space. Reversing parity is what flips the direction of space, and obviously, reversing time makes it run backwards. Having a mirror universe keeps CPT symmetry together.
If the Big Bang is a mirror, then we are on one side. The aftermath of the explosion that is thought to have birthed the universe would be asymmetrical if there was no reflection. Seeing the universe as an object in itself, instead of a mashup of different forces and fields that each have their own interactions, gives it an anti-universe under CPT symmetry. It can only achieve symmetry when it has its own opposite in which time runs backwards. If this is reality, then what is defined as a vacuum state, void of particles, leads us to seeing dark matter.
“An observer like us, long after the Big Bang, defines one type of vacuum state,” Boyle said. “The fields of nature are actually in a different vacuum state. Because these two states are different, we interpret the universe as being full of a certain non-zero density of these particles.”
These fields, which are in the CPT-symmetric vacuum state, include the field of that bizarre theoretical particle, the right-handed neutrino. It is thought to be different from every other particle because there is no other force it interacts with besides gravity. This is how dark matter behaves. It is invisible, intangible, inaudible, in-everything else, but its gravitational force can explain phenomena such as galactic collisions. If Einstein’s theory of gravity joins forces with quantum mechanics, it is possible for individual observers to see different vacuum states.
Here is where dark matter could be revealed. The Big Bang is seen as having one vacuum state, while fields, including the right-handed neutrino field, have another. If we existed in the same vacuum state as right-handed neutrinos, space would be devoid of these particles. However, because we exist in the Big Bang vacuum state, that means particles in all other fields have to exist, meaning the right-handed neutrino must exist. That would also mean that it is out there behaving like dark matter. Suddenly dark matter has particles that can be detected.
“Our predictions can be tested observationally,” said Boyle. “If the theory does not pass these tests, it will be ruled out. If a value that is measured does not agree with the value we have predicted, then our theory is not correct.”
Of course, this means “and vice versa.” The theory that he and his team came up with predicts things such as the lightest neutrino masses, which is something that is actually being measured and may have an answer within a few years. It also predicts that there were no primordial gravitational waves. If gravitational waves from the beginning of time are found, as opposed to those that later resulted from black holes or neutron stars crashing into each other, that would also disprove it. Prove the theory right and you’ve got a way to see dark matter.
This will really give you something to think about in the middle of the night, no SYFY marathon required.