An anti-Universe could exist in reverse time before the Big Bang, theory suggests

“You have always lived in the past, present, and future” Albert Einstein

TL;DR

A new theory proposes the existence of a mirror universe running in reverse time before the Big Bang. This anti-universe would obey CPT symmetry and could explain dark matter as right-handed neutrinos. It might also remove the need for cosmic inflation. Future experiments on gravitational waves and neutrino mass could provide evidence for this theory, changing our understanding of the universe’s origins.

A radical new theory proposes the existence of an “anti-universe” running in reverse time before the Big Bang.

This concept suggests that the early universe was so small, hot, and dense, and so symmetrical, that time could move in both directions.

If this theory is correct, it may explain dark matter as a new form of neutrino that only exists in such a universe. Additionally, it would eliminate the need for an “inflation” period that supposedly caused the young universe to expand rapidly.

If proven true, future experiments searching for gravitational waves or determining the mass of neutrinos could provide definitive evidence for the existence of this mirror anti-universe.

Preserving Symmetry

Physicists have uncovered fundamental symmetries in nature. The three most important ones are: charge (if all particle charges are flipped to their opposites, interactions remain the same); parity (interactions appear the same in a mirror image); and time (if an interaction is reversed in time, it behaves similarly).

Most physical interactions follow these symmetries most of the time, although some violations occur. However, no one has ever seen a violation of all three symmetries combined. If you flip the charge, mirror the interaction, and reverse time, the interaction still behaves identically.

This essential symmetry is known as CPT symmetry, which stands for charge (C), parity (P), and time (T).

In a recent paper set to be published in Annals of Physics, scientists propose extending this symmetry. While it usually applies to interactions like forces and fields, they suggest that this symmetry might apply to the entire universe itself. Instead of just affecting the “actors” (forces and fields), it may also govern the “stage” — the entire universe as a physical object.

Creating Dark Matter
Our universe is expanding and filled with particles moving forward in time. By applying CPT symmetry to the entire cosmos, we realize our universe may not be the full story.

To maintain CPT symmetry, there could be a mirror universe that balances ours. This twin universe would have opposite charges, be reversed in a mirror, and move backward in time. Together, these two universes would obey CPT symmetry.

The researchers explored the implications of this idea and found several intriguing results.

Firstly, a CPT-symmetric universe would expand and fill itself with particles naturally, without the need for inflation. While there’s significant evidence supporting inflation, its theoretical framework is unclear, leaving space for alternative theories.

Secondly, a CPT-symmetric universe would introduce additional neutrinos. Currently, we know of three neutrino flavors: electron, muon, and tau neutrinos, all of which are left-handed (their spin aligns with their motion). In contrast, other particles come in both left- and right-handed versions, raising the question of whether right-handed neutrinos exist.

A CPT-symmetric universe would require at least one right-handed neutrino, which would be invisible to most physics experiments but would still affect the universe through gravity.

An unseen particle that fills the universe and only interacts via gravity sounds a lot like dark matter.

The researchers concluded that the conditions needed to maintain CPT symmetry would fill our universe with right-handed neutrinos, enough to explain dark matter.

Predictions in the Mirror

Although we could never directly observe this CPT-mirror universe, as it exists “before” our Big Bang, we can still test the theory.

The researchers made several predictions. For one, they suggested the three known left-handed neutrinos should be Majorana particles, meaning they are their own antiparticles (unlike regular particles like electrons, which have distinct antimatter counterparts called positrons). Currently, scientists are uncertain whether neutrinos have this property.

They also predicted that one of the neutrino types should be massless. While physicists have only set upper limits on neutrino masses so far, if one of them is found to be massless, it would strongly support the CPT-symmetric universe theory.

Finally, in this model, inflation never occurred. Instead, the universe naturally filled with particles on its own. Physicists believe that inflation disrupted space-time so much that it generated gravitational waves across the cosmos. Many experiments are searching for these primordial gravitational waves. However, in a CPT-symmetric universe, no such waves should exist. If these experiments fail to detect primordial gravitational waves, it might indicate that the CPT-mirror universe theory is correct.