CP violation as a solution to the Ozma Problem

The Ozma problem, a puzzle introduced in 1964 by Martin Gardner, 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. Furthermore, it is complicated 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.

Ozma Problem

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, linear momentum, and electric field are some of the quantities that flip under a parity transformation.

Parity conservation through parity symmetry or P-Symmetry was believed up until 1956 to be a universal and fundamental law. Physicists thought that the laws of physics remain the same if the system under consideration is mirror inversed. A concept characterized by the fact that any physical process or transformation and its mirror image yields similar products and occurs simultaneously. Both processes are indistinguishable from one another on all scales. But the fact had only been tested in electromagnetic interactions and not weak interaction, the force governing subatomic decay.

P-Symmetry violation

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 atomic nucleus emits an electron) 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.

Chien Wu and her experiment
Chien Wu was popularly called The First Lady of Physics.

Chien Wu experimentally observed the parity violation in weak decay. She was a genius. Back then, there was a saying among the physicists that if Wu experiments, it must be correct. You can read about that experiment and 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.

The Mirror Of The Universe: Understanding The Famous Ozma Problem In Science. 1

In other words, suppose you want to communicate with an alien civilization. The only way 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.


The Mirror Of The Universe: Understanding The Famous Ozma Problem In Science. 2
The CP transformation

Our universe’s more complex symmetrical projection 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 involves 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 taking the mirror image of a system and replacing the system’s particles with their antiparticles.

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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

CP-Symmetry violation or CP violation, also explained as the asymmetry between matter and antimatter, was discovered in the subatomic decay of kaons, a fast decaying subatomic particle made of four mesons, each composed of one quark and antiquark bound together by the strong interaction. In 1964, Kaons (and 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. 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 because 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.

The universe is symmetrical and does not distinguish between left and right or matter and antimatter. However, on subatomic scales where the weak nuclear force governs processes, charge conjugation and parity symmetry breakdown.

Matter-Antimatter imbalance

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 provides many insights into the field of particle physics. For example, the Ozma problem appeared in the book called ‘The Ambidextrous Universe.’

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