The ultimate goal of modern theoretical physics is to find a Theory of Everything (ToE)—a single, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe.
The Standard Model
Currently, our best understanding of the universe at the fundamental level is encapsulated in the Standard Model of Particle Physics. It describes three of the four known fundamental forces:
- The Electromagnetic Force (carried by photons)
- The Strong Nuclear Force (carried by gluons, binding protons and neutrons)
- The Weak Nuclear Force (carried by W and Z bosons, responsible for radioactive decay)
It also classifies all known elementary particles, such as quarks (which make up protons and neutrons) and leptons (such as electrons).
The Problem of Gravity
The glaring omission from the Standard Model is the fourth fundamental force: Gravity. While gravity is brilliantly described on a macroscopic scale by Einstein's General Relativity, attempting to combine General Relativity with Quantum Mechanics mathematically leads to nonsensical infinities.
Current advanced theories, such as String Theory and Loop Quantum Gravity, are attempts to reconcile these two pillars of modern physics into a unified framework of Quantum Gravity.