Reflections

Yoichiro Nambu, Makoto Kobayashi and Toshihide Maskawa shared the Nobel Prize for Physics this year for their discoveries related to Spontaneous Symmetry Breaking. Symmetry is a very basic property of nature. We can see it around. Human body itself is symmetric about a vertical axis. Laws of Physics also manifest this symmetry as in the case of conservation of energy.

Earlier scientists were thinking that the nature conserves three symmetries- Charge conjugation, Parity and Time. A symmetry of a physical system is a physical or mathematical feature of the system (observed or intrinsic) that is “preserved” under some change. For example, a sphere will appear the same, even if it’s rotated; thus it can be said to possess spherical symmetry. The CPT theorem holds that the universe (or the physical laws that govern them) will be invariant

• even if we replace the particles with anti particles (charge symmetry)
• even if we observe the universe through a three dimensional mirror (parity symmetry)
• even if the time is reversed- just like a movie played in reverse (time symmetry)

But later experiments proved that these symmetries are violated in certain cases. Now, the accepted idea is that the combined symmetry of CPT is preserved.

We can witness symmetry violations in everyday life. A pencil standing on its point leads a completely symmetrical existence in which all directions are equal. A small perturbation can cause the pencil to topple. It can fall in any direction, without a preferred direction. The symmetry is lost when it falls over.

Violation of symmetries explains how we exist. In the universe, there are particles and anti particles. In the big bang which created our universe, matter and antimatter were there in equal amounts. If a particle and its antiparticle meet together, they just annihilate into a flash of energy. But then, how the universe as we see exist? That’s the result of Spontaneous Symmetry Breaking. By chance, amount of matter exceeded the amount of antimatter. This symmetry breaking resulted in our existence.