Can Anti-Universes Exist?
The physics of C, P and T-Symmetries
You can recognize a pioneer by the arrows in his back. - Beverly Rubik
Greetings, fellow Bohron
Now that we understand that antiparticles can exist, it’s time to scale up and see if the same reasoning can be carried out to propose the existence of anti universes. Let’s find out.
Antigravity and Anti-Universes
We know that particles differ from their antiparticle counterparts only in the respect that they carry opposite charges. However, not all particles that occur in nature carry an intrinsic charge.
For example, photon which makes up light, and graviton which is believed to be elementary particle that mediates the gravitational force; carry no charge at all. Such particles can be their own antiparticle. This means that gravity and antigravity are a lot similar.
Symmetries in Nature
A physical/mathematical feature of a physical system is said to be symmetric if it remains unchanged under some transformation.
One of the most notable examples of symmetry in physics is the second postulate of the special theory of relativity: the speed of light is constant in all frames of reference.
These state that the universe in which we live should be indistinguishable from one where a certain type of change is introduced.
Symmetries in Particle Physics
In particle physics, we study these three symmetries:
C-symmetry
A universe where every particle possesses an opposite charge. Such a universe is made entirely of antimatter. C stands for Charge.
C-Reversal. Source P-symmetry
A universe where everything is a mirror image of itself. P stands for Parity. It is also known as Looking Glass Universe.
P-Reversal. Source T-symmetry
A universe where the direction of time is reversed. T stands for Time. We encounter such a world in Christopher Nolan’s sci-fi movie Tenet. In a T-reversed universe, corpses rise from the dead, get younger, turn into babies, and then jump into their mother's wombs.
In this scene from Tenet, an overturned car flips right-side up because time travels in reverse. Source
Are C-reversed and P-reversed universes in principle possible?
By examining the nature of weak forces, C. N. Yang and T. D. Lee of Columbia University showed that the P-reversed universe cannot exist. This means that nature does not always behave in exactly the same way when seen in the mirror. For this shocking discovery, Yang and Lee won the Nobel Prize in Physics in 1957.
Similarly, a C-reversed universe is also not possible. It also fails to obey the known laws of physics
What about a T-reversed universe?
Special relativity says that space and time are related. Since spatial symmetry is not allowed, so should be the case with temporal symmetry. And that’s what was indeed found. T-reversal violates the laws of quantum mechanics.
So, I wasn’t completely correct in calling them symmetries since they aren’t obeyed in our universe. Hence, it’s better to call them “near-symmetries”.
Now consider a universe which is both charge and parity-reversed i.e. it is composed of antimatter as well as left and right interchanged. Can such a CP reversed universe exist?
The work James Cronin and Val Fitch did in 1964 showed that even the CP-reversed universe could not exist. Why? No one knows.
By analyzing the properties of subatomic particles, it is still possible to tell the difference between left-right, clockwise or counterclockwise. For this discovery, Cronin and Fitch won the Nobel Prize in 1980.
This result is known as CP Violation and is one of the greatest unsolved mysteries in physics.
Similarly, CT and PT violations also exist.
If we reversed the charges, the parity, and the march of time, then the resulting universe would obey all the laws of physics. The CPT-reversed universe is allowed. To date, no experimental proof of CPT violation has ever been found.
So if the search for an antiuniverse yields a fruitful result, the universe would be CPT symmetric in nature. And this is what we know till now.
Sources:
Ch 10, Physics of the Impossible, Michio Kaku
Symmetry (physics) - Wikipedia