Physics is the scientific study of how the universe works. It is the most fundamental of the natural sciences, seeking to explain everything from why things fall to the ground, to why stars shine, and how energy moves through space.
At its core, physics tries to answer simple but profound questions:
- What is matter made of?
- How does matter move through space and time?
- What are the fundamental forces that govern the universe?
When you throw a ball, ride a bicycle, or look at a rainbow, you are observing physics in action.
Physics is broadly divided into two main eras: Classical Physics and Modern Physics.
Classical Physics
This encompasses the laws and theories developed before the 20th century.
- Classical Mechanics: Formulated by Sir Isaac Newton, this branch studies the motion of macroscopic objects. It introduces concepts like inertia, momentum, and the famous equation (Force equals mass times acceleration).
- Electromagnetism: Unified by James Clerk Maxwell, this branch explains how electric fields and magnetic fields interact to produce light and radio waves.
- Thermodynamics: The study of heat, work, temperature, and the statistical behavior of systems.
Modern Physics
At the turn of the 20th century, scientists realized classical physics failed to explain the behavior of things that were extremely fast or extremely small.
- Relativity: Albert Einstein's theories describing the behavior of objects moving near the speed of light, and redefining gravity as the curvature of spacetime.
- Quantum Mechanics: The study of the atomic and subatomic world, where energy is quantized and particles exhibit wave-like behavior.
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.