February 20, 2019

## Symmetry in Theoretical Physics

### From Newton to the Standard Model to GUTs to SUSY and Beyond

Abstract: Classical physics includes many important conservation laws which were established through experiment. Looking back these conservation laws can be explained as the consequence of symmetry. For the advancement of Modern Physics in the early Twentieth Century, theory, including applications of symmetry, played a vital role in the understanding of relativity, particle spin and anti-matter. Theoretical considerations of symmetries and broken symmetry led the development of the Standard Model of Elementary Particles, and these same considerations provide tantalizing clues to what may yet be discovered. This discussion will provide a high-level overview of these concepts without all of the mathematics and technical complications. The slides may be viewed here.

## Why is my logo an apple with a funny diagram on it?

I wanted an attention-grabbing logo for my web site, but it had to be reasonably simple. I merged a few different physics concepts, and this is what resulted. It’s not really important for everybody to understand what it means to me.

I started with an apple. That much might be obvious as many people know the story about Isaac Newton. He made the incredible leap that the motion of a falling apple and the motion of stars and planets are determined by the same force called gravity.

The diagram drawn on the apple is slightly distorted due to the curvature of the surface of the fruit. This is suggestive of Albert Einstein’s General Theory of Relativity which describes gravity as the warped geometry of space-time. I actually got that idea from staring at the cover of Gravitation by Misner, Thorne and Wheeler.

The diagram itself is a Feynman diagram from Quantum Field Theory describing the interaction of three photon-like particles through the exchange of electron-like particles. The numeric value of this diagram is actually infinite, and it would indicate that the various components of the Standard Model of Elementary Particle Physics should fail. However, the contributions of the Electromagnetic, Weak Nuclear and Strong Nuclear forces conspire in such a way that the offensive infinities cancel exactly.

This very strongly suggests that the parts combine in a unified theory and is the basis of the idea of the Grand Unified Theory (GUTs). While such theories have not yet been experimentally successful it is generally believed that unification is manifest, and eventually gravity will be part of the unified theory, and we return full-circle to gravity.

In brief, this image represents to me the past, present and future of physics.

While the concept is mine, I wanted help from an artistic person who could go far beyond my white-board doodling. I thank Sharon Neveu for her excellent work!

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