Why Matter Exists in the Universe
Parity (P), Charge Conjugation (C), Time Reversal (T) symmetries and the cosmic mysteries they unlock
When physical laws remain unchanged under certain transformations. For example, if the same laws apply in a mirror reflection, we have 'parity symmetry'.
Space Inversion Symmetry
Physical laws remain the same when spatial coordinates are inverted (x → -x)
The same laws should apply in a mirror world... or so we thought
Particle-Antiparticle Symmetry
Physical laws remain the same when particles are replaced with antiparticles
Swapping electrons for positrons, quarks for antiquarks should yield the same physics
Time Reversal Symmetry
Physical 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)
Lee and Yang proposed that parity might not be conserved in the 'weak force'
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 violation
Cronin and Fitch discovered CP violation in K mesons (1980 Nobel Prize)
Showed that CP violation can be explained by assuming 6 types of quarks
Belle (Japan) and BaBar (USA) experiments directly observed CP violation in B mesons
Makoto Kobayashi and Toshihide Maskawa received the Nobel Prize for 'discovery of the origin of broken symmetry'
The radioactive isotope that first proved parity violation in 1957
The meson that first showed CP violation in 1964
Shows CP violation more clearly. Contributed to the 2008 Nobel Prize
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.