We will first present an organizational view of the subfields and concepts of physics and then outline their contents and interrelationships in a narrative. See /Schemes for alternative presentations.
What are our priorities for writing in this area? To help develop a list of the most basic topics in Physics, please see Physics basic topics.
Physics (Greek phusis: nature) studies all aspects of nature: matter and energy, the fundamental forces acting on matter and energy, and the concepts of space and time. It attempts to discern physical laws which are expressed using the language of mathematics.
Historically, people tried to understand the movements of the stars in the sky and also several phenomena on Earth, for instance the fact that objects drop to the floor. People also speculated about the ultimate small-scale nature of matter. Several theories were proposed, but in the absense of systematic experimental tests, most of them were unsupported and wrong. A notable exception is the work of Archimedes, who, among his many inventions, also discovered several laws of mechanics and hydrostatics.
One of the first useful, comprehensive and approximately correct physical theories was that of gravity, the fundamental force causing all objects to attract each other. Building on the work of Galileo, Newton in the seventeenth century was able to formulate a comprehensive theory that is now known as classical mechanics. He had to develop the mathematical tool of calculus and introduce the important unifying concept of force for this purpose. Newton's theory was able to correctly predict the movement of the planets and the falling of objects on Earth. Much later, Einstein presented his general theory of relativity, a theory of gravity whose predictions are slightly more accurate than Newton's and which views gravity as an effect of the curvature of spacetime.
Using methods of statistical mechanics, Newton's laws could also be used to understand phenomena such as temperature and heat as the consequence of random movements of large numbers of small particles; this led to a better understanding of the physical theory of thermodynamics.
The phenomena of electricity and magnetism are currently best described by Maxwell's equations of electromagnetism, which led to the insight that light is an electromagnetic wave. Einstein, starting with Maxwell's equations and the principle that the physical laws should be the same for moving observers, formulated his theory of special relativity, which changed Newton's absolute concept of time to a relative one which depends on the observer. Furthermore, special relativity holds that energy and mass are ultimately different forms of the same underlying fundamental concept, mass-energy. The understanding of electricity also paved the way for the development of electronics and ultimately led to the construction of computers.
The current model about the structure of matter was not fully formulated until the early twentieth century: the chemical elements consist of atoms, which in turn consists of a nucleus of protons and neutrons surrounded by electrons. Particle physics has probed the structure of protons and neutrons, and today it is believed that they are made up of quarks held together by the strong interaction.
Small particles like these exhibit strange wave-like behaviors, and this wave-particle duality was ultimately explained by quantum mechanics. Light is then seen as a stream of particles called photons, and physics can only predict the probabilities of different measurement outcomes, but not the measurement outcomes themselves.
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