Just like Thanos in Avengers, our physical laws are obsessed with balance and symmetry. But the universe doesn’t really ascribe to that. Physics tell us that matter and antimatter are equal and should have existed in equal form after the Big Bang, but in reality, we have a universe made almost exclusively of matter.
We have no solution for this glaring discrepancy, it is a limit of our current theories. Many solutions have been proposed to explain it, but they are all yet to be confirmed. Now, a recent and rather outlandish new theory suggests that our universe has a mirror anti-matter companion expanding backward in time from the Big Bang. This hypothesis is presented in the journal Physical Review Letters.
Before we get into the details of this "mirror universe" it's important to understand where the idea comes from. Since the 1950s, scientists have discovered that certain phenomena have the ability to violate some long-established symmetries of the universe.
One is called parity (P), which is the idea that if you flip all your spatial coordinates (up becomes down, in becomes out, left becomes right), physics will still behave in the same way. Another one is called charge (C), which posits switching matter for antimatter should result in the same physics. But that’s not always the case. At first many of these violations were solved by using the combined CP symmetry, but then researchers found violations in this too, so they added time (T) to the equation. The principle goes that something may be able to break one (or two) of the symmetries of physics, but nothing should be able to break the combined CPT symmetry.
This new study uses this approach for the entire universe. They argue that the universe doesn’t violate CPT as our matter-dominated universe, expanding in a certain direction in time from the Big Bang, is the mirror image of an anti-matter dominated universe that existed before the Big Bang.
This theory has some interesting advantages. It doesn’t require us to build new physics to explain several complicated events in the evolution of the universe, such as Cosmic Inflation, the extremely rapid expansion of the universe in the fraction of seconds after the Big Bang. It also comes up with a possible candidate for dark matter, as this setup would produce an excess of massive hypothetical particles known as sterile neutrinos.
It is, however, far from a perfect theory. It doesn’t explain for example the temperature fluctuations in the Cosmic Microwave Background – the universe should be filled with radiation that is the remnant heat left over from the Big Bang after the gas cooled – which has been a cornerstone of cosmological models since their discovery. The team is working on solving these issues. And if they do they can also tell us if the mirror universe is populated by evil versions of ourselves.
[H/T: Physics World]