Scientists believe there could be an ‘anti-universe’ next to ours – where time runs backwards

A wild theory suggests there may be an "anti-universe" that runs backwards in time before the Big Bang.

The concept, explained in a paper accepted for publication in the journal Annals of Physics, suggests that the reason for this universe is because there are fundamental symmetries in nature – such as charge, parity, and time. This fundamental symmetry is known as CPT symmetry.

Physical interactions generally obey these symmetries, but physicists have never observed a violation of these laws of nature simultaneously. The researchers posit that while this symmetry applies to interactions, it could also apply to the entire universe.

As such, to preserve this symmetry, there could be a mirror-image cosmos to balance our own.

The consequences to this universe existing could explain dark matter. There are currently three known types of neutrino: electron-neutrinos, muon-neutrinos and tau-neutrinos, all of which spin in the same leftwards direction. Physicists have wondered if there might be right-spinning neutrinos, but have never detected them.

A reverse universe would necessitate the existence of one of these new kind of neutrinos, but it would be undetected in physics experiments and could only interact with the universe through gravity – similar to dark matter.

If true, the number of right-spinning neutrinos in our universe would be enough to account for the dark matter physicists have detected, Live Science reports.

Although we would never be able to access this universe, because it exists prior to the Big Bang, scientists can test the hypothesis. They predict that the three known neutrino kinds would also be their own antiparticles (in contrast to electrons, for example, whose antiparticles are positrons). This classification is known as Majorana particles; currently, scientists do not know if neutrinos have this characteristic.

Moreover, one of these new kinds of neutrinos should be massless – and should physicists ever be able to conclusively measure the mass of these subatomic particles, and discover they have none, it would reinforce this theory.

Finally in this model inflation, the natural expansion of the universe, has not occurred. Physicists believe that inflation had such an effect on space-time that gravitational waves flooded the universe, but in this alternate universe no waves should exist. Under experiments, if primordial gravitational waves are not found, this could reveal that a CPT-mirror universe model is accurate.