Our universe may have a twin that runs backward in time

There is a new theory that suggests there may be another anti-universe in the future.

The idea is that the early universe was small, hot and dense, and so uniform that time looks backwards and forwards.

The new theory says that dark matter is just a new flavor of a ghostly particle. The theory suggests there would be no need for a period of inflation that rapidly expanded the size of the young universe.

If true, future experiments could answer the question of whether or not the mirror anti-universe exists.

Preserving symmetry

Physicists have found a set of fundamental symmetries. If you flip the charges of all the particles involved in an interaction to their opposite charges, you will get the same interaction.

Most of the time, physical interactions obey the symmetries, which means there are sometimes violations. Physicists have never observed a violation of all three symmetries at the same time. If you flip the charges and take the mirror image and run it back in time, the interactions will behave the same.

The name of the fundamental symmetry is "C, P, and Time".

What is multiverse theory?

Scientists propose extending the combined symmetry in a new paper accepted for publication. This symmetry only applies to the forces and fields that make up the physics of the universe. If this is such an important symmetry, it applies to the entire universe. This idea extends the symmetry from the actors of the universe to the stage of the universe.

Creating dark matter

We live in a universe that is expanding. The evolution of the universe is moving forward in time, because the universe is filled with lots of particles. Our view of the universe can't be the entire picture if we extend the concept of CPT symmetry to our entire cosmos.

There must be more. There must be a mirror-image cosmos that balances out our own. This universe would have different charges than we have, and it would run in time. Our universe is a twin. The two universes obey the same symmetry.

The researchers asked what the consequences would be.

They found a lot of wonderful things.

A universe that is CPT-respecting naturally expands and fills itself with particles, without the need for a long-theorized period of rapid expansion known as inflation. There is a lot of evidence that inflation happened, but the picture of the event is fuzzy. There is a lot of room for viable alternatives.

There would be some additional neutrinos added to the mix. There are three different flavors of the neutrino. All three of these flavors are left-handed. Physicists have wondered if there are more right-handed neutrinos in the other particles.

The existence of at least one right-handed neutrino species would be demanded by a CPT-respecting universe. The rest of the universe would only ever be influenced by this species through gravity.

An invisible particle that only interacts with gravity sounds a lot like dark matter.

The researchers found that the conditions imposed by obeying CPT symmetry would fill our universe with right-handed neutrinos, enough to account for the dark matter.

Predictions in the mirror

We wouldn't have access to our twin, the mirror universe, because it's behind our big bang. We can still test this idea.

There are a few observational consequences of this idea. They think that the three known left-handed neutrino species should all be Majorana particles, which means that they are their own antiparticles. Physicists are unsure if neutrinos have this property.

They predict that one of the species should be massless. Physicists can only place upper limits on the neutrino mass. The idea of a CPT-symmetric universe would be greatly strengthened if physicists could measure the mass of the neutrinos.

The event of inflation never occurred in this model. The universe was filled with particles on its own. Inflation shook space-time to such a degree that it created ripples in the universe. There are many experiments looking for primordial waves. No such waves should exist in the universe. If the searches for primordial waves turn out to be empty, that could be a sign that the universe model is correct.

It was originally published on Live Science.