CP violation as a solution to the Ozma Problem
Introduced in 1964 by Martin Gardner, was a conundrum known as the Ozma Problem, which addresses the impossibility of communicating the difference between left and right with distant being, due to the absence of a common point of reference (such as a stellar body). However on this macroscopic scale, even distant objects are difficult to label as left and right for there is no tangible difference between an object viewed as a left-handed or right-handed system, and it is especially different to assign a label without any behavioral discrepancy between an object or its symmetry: the left-right ambiguity. As such, objects virtually look the same when flipped over like in a mirror, a process known as parity transformation.
Parity transformation involves flipping the spatial coordinates and replacing them with their negative counterparts i.e. (x,y,z) are replaced by (-x,-y,-z) – the mirror image of the universe. Some physical quantities remain invariant under in their mirror image. They include time, mass, the energy of a particle, magnetic field, etc. However, position, momentum, linear momentum, electric field are some of the quantities that are invariant under a parity transformation.
Parity conservation through parity symmetry or P-Symmetry was believed up until 1956 to be a universal and fundamental law. A concept characterized by the fact that any physical processes or transformation and its mirror image yields similar products and occurs at the same rate. As such, both processes are said to be indistinguishable from one another on all scales, but have only been tested in electromagnetic interactions and not in the case of weak interaction, the force which governs subatomic decay.
In 1956, P-Symmetry was tested experimentally on processes governed by the weak force in an experiment on beta decay (a radioactive decay in which an electron is emitted by an atomic nucleus) on a cobalt-60 nucleus which proved that weak interactions do in effect violate the P-Symmetry, that depending on if they belong to the right or left-handed systems do not change according to their symmetrical projection.
The parity violation in weak decay was experimentally observed by Chien Wu. She was a genius. Back then there was a saying among the physicists that if an experiment is done by Wu, it must be correct. You can read about that experiment and about Wu in this article.
More than often, when these subatomic decays occur, the spin of the electrons released in the reaction remains unchanged. As such, looking at electron spin would help define left and right independently of if the perception that the individuals we are interacting with is a translation or symmetry of ours, solving the left-right ambiguity.
In other words, suppose you want to communicate with an alien civilization. The only way in which you could tell them about the left-right of the universe is to ask them to observe the decay of the Co-60 in a magnetic field. This is the only experiment by which they can solve the left-right ambiguity.
A more complex symmetrical projection of our universe involves parity (left-right inversion) and charge conjugation (matter and antimatter). This projection known as CP-Symmetry is the product of two transformations. So if parity involved flipping the coordinates of a system by their negatives, charge conjugation involves replacing the particles with their corresponding antiparticles (opposite charge). Together, CP operation means first taking the mirror image of a system and then replacing the particles of the system with their antiparticles.
- Understanding the Dirac equation and antimatter
- The importance of Feynman diagrams in physics
- The standard model of physics
So now we have to consider yet another possibility. What if the aliens are made up of antimatter and they are watching the decay of antimatter-Co-60? So is there any way by which we can overcome this problem? In 1964, scientists found a way out!
CP-Symmetry violation or CP violation, explained also as being the asymmetry between matter and antimatter, was discovered in the subatomic decay of kaons, a fast decaying subatomic particle made of groups of four mesons each composed of one quark and antiquark bound together by the strong interaction. In 1964, Kaons (as well as anti-kaons) were seen to decay less often into left-handed electrons. As such, kaons behaved similarly in decay regardless of the nature of their charge conjugation.
We tell the aliens how to watch kaons decay (for example) and then the aliens can figure out whether they’re made of (what we call) matter or antimatter, and therefore they can figure out which way is left and right without any more ambiguity, thus solving the Ozma problem.
A more complex version of the Ozma Problem, in which an object and its transformation through CP symmetry were indistinguishable due to the fact that antimatter and matter have the same spectrum posed the following question: how to figure out if a distant object is a matter or antimatter. The observation of electron parity in the subatomic decay of kaons would, as such, provide a point of reference to tell matter from antimatter, as well as telling left from right.
As such, the universe is symmetrical and does not distinguish between left and right or matter and antimatter. However, on subatomic scales where processes are governed by the weak nuclear force, charge conjugation and parity symmetry breakdown.
Other than allowing different versions of the Ozma Problem to be solved, the violation of CP-Symmetry is necessary to explain why there is more baryonic than non-baryonic matter in the universe: the matter-antimatter imbalance. However, CP violation does not come close to account for the full discrepancy in the amounts of matter and antimatter.
The Ozma problem gives many insights into the field of particle physics. Ozma problem appeared in the book called ‘The Ambidextrous Universe’.