Dark Matter Mystery Solved By Mirror Universe Running Backwards

Physicists have determined that the laws of nature tend to follow three fundamental symmetries, that of charge, parity, and time, known collectively as CPT symmetry. A preprint of the article, which has been accepted for publication in the journal Annals of Physics but has not yet been peer-reviewed, can be read on the arXiv repository, Ian Randall reported for Daily Express.

Photo Insert: The starting point for this thought experiment came from “a simple observation” — that in the hot, radiation-dominated era of the early universe that began less than a minute after the Big Bang, the maths describing the background universe has time-reversal symmetry.

What this means, in theory, is that if you were to consider the interactions between any particles, you could reverse the charges (switch matter with antimatter, for example); replace every particle, interaction, and decay with its mirror image (a so-called parity transformation); or run the interaction backward instead of forwards in time — and it would still behave the same.

In reality, however, things are a little more complicated, as sometimes individual symmetries aren’t followed, in what physicists call a “violation.”

If we take neutrinos, for example — subatomic particles that are similar to electrons, but with no electrical charge and a minimal mass — they are thought to always spin clockwise relative to the direction in which they are traveling.

Physicists call this “left-handedness”; if you hold out your hand with your thumb pointing towards you and your fingers bent, you’ll see that your fingers curl around the thumb’s axis in a clockwise direction. Because all known neutrinos are left-handed, you can’t perform a parity transformation on them, as the mirror image would be a right-handed neutrino, which doesn't seem to exist.

Similarly, as antineutrinos are always right-handed, you can’t perform a charge transformation on a neutrino, as you would have to end up with a left-handed antineutrino.

While individual symmetries have been seen to be violated, no system has ever violated all the three parts of CPT symmetry at once — it appears to be fundamental. In their study, Dr. Latham Boyle and his colleagues at the Perimeter Institute for Theoretical Physics in Waterloo, Canada propose extending the scope of CPT symmetry.

They set out to explore whether it might apply not just to basic interactions within the universe, but also to the very universe itself.

According to the trio, the starting point for this thought experiment came from “a simple observation” — that in the hot, radiation-dominated era of the early universe that began less than a minute after the Big Bang, the maths describing the background universe has time-reversal symmetry.

They added: “We interpret this as a clue that the state of the universe (i.e. the spacetime itself as well as the quantum state of quantum field theory on that spacetime) might actually respect CPT symmetry.”

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