P (Parity)
Space Inversion SymmetryPhysical laws remain the same when spatial coordinates are inverted (x → -x)
The same laws should apply in a mirror world... or so we thought
SOUL/ALLOY Science · Fundamental Physics
Symmetry Breaking
Why Matter Exists in the Universe
Parity (P), Charge Conjugation (C), Time Reversal (T) symmetries and the cosmic mysteries they unlock
What is Symmetry?
When physical laws remain unchanged under certain transformations. For example, if the same laws apply in a mirror reflection, we have 'parity symmetry'.
Three Fundamental Symmetries
C (Charge Conjugation)
Particle-Antiparticle SymmetryPhysical laws remain the same when particles are replaced with antiparticles
Swapping electrons for positrons, quarks for antiquarks should yield the same physics
T (Time Reversal)
Time Reversal SymmetryPhysical laws remain the same when time direction is reversed
Playing a movie backwards shouldn't violate physical laws
CPT Theorem
When C, P, and T are all applied together, physical laws must remain invariant (this cannot be broken)
History of Symmetry Breaking
Theoretical Prediction
Lee and Yang proposed that parity might not be conserved in the 'weak force'
Wu Experiment
First experimental proof of parity violation using Cobalt-60 beta decay. One of the most important physics experiments in history
Co-60 nuclei were aligned using a magnetic field at extremely low temperature (0.01K), and the angular distribution of beta electrons was measured. Electrons were preferentially emitted opposite to the nuclear spin. This would be reversed in a mirror world = proof of parity violationCP Violation Discovery
Cronin and Fitch discovered CP violation in K mesons (1980 Nobel Prize)
Kobayashi-Maskawa Theory
Showed that CP violation can be explained by assuming 6 types of quarks
CP Violation in B Mesons
Belle (Japan) and BaBar (USA) experiments directly observed CP violation in B mesons
Nobel Prize in Physics
Makoto Kobayashi and Toshihide Maskawa received the Nobel Prize for 'discovery of the origin of broken symmetry'
Particles and Symmetry Breaking
Why is the Universe Made of Matter?
Right after the Big Bang, matter and antimatter should have been created in equal amounts. Yet today's universe is matter-only. Why?
CP symmetry breaking caused slight differences in how matter and antimatter behave. This 'asymmetry' created a matter-dominated universe.
However, the known CP violation alone cannot fully explain the universe's matter dominance. New physics may be needed.