Scientists studying symmetries have posed a theory that there may be an ‘anti-universe’ outside of our own where time runs backwards.
The theory is based on the knowledge that there is a set of fundamental symmetries in nature, the most important of which are charge, parity and time.
Specifically, if you flip the charges of particulars in an interaction to their opposite charge, the same interaction takes place (charge). If you look at a mirror image of an interaction you get the same result (parity), and if you run an interaction backwards in time, it looks the same (time).
There are sometimes violations to these symmetries, but physicists have never observed a violation of a combination of all three symmetries at the same time. This fundamental symmetry has been dubbed CPT, in reference to charge, parity and time.
In a new paper recently accepted for publication in the journal Annals of Physics, scientists propose extending this concept of combined symmetry to the entire universe, suggesting the early universe was small, hot and dense, and so uniform that time looks symmetric going both backwards and forwards, LiveScience reports.
With that concept in mind, the view of our own universe – where evolution moves forwards in time – must be extended to include a mirror-image which runs backwards in time.
The theory may offer an explanation for the existence of dark matter, with scientists suggesting it may be an invisible particle which interacts only via gravity and which offers the twin to three known neutrino flavors in our own universe; the electron-neutrino, muon-neutrino and tau-neutrino.
All three of these neutrino flavors are described as left-handed due to the direction of the spin relative to the motion, and all other known particles in physics have both left and right-handed versions. If the universe did respect the rules of CPT, it would demand the existence of at least one right-handed neutrino species.
Researchers found that the conditions created with such a universe would mean it was full of right-handed neutrinos, enough to account for the dark matter.
As well as offering a potential explanation for dark matter, the theory implies there would be no need for a period of ‘inflation’ after the Big Bang to rapidly expand the size of the cosmos because a CPT-respecting universe would naturally expand and fill itself with particles.
We would never be able to access this alternative universe if it did exist, but future experiments to search for gravitational waves or to confirm the mass of neutrinos could work to prove the theory correct.
