Theoretical physics attempts to understand the world by making a model of reality, used for rationalizing, explaining, predicting physical phenomena through a "physical theory". There are three types of theories in physics; mainstream theories, proposed theories and fringe theories.

Some physical theories are backed by observation, whereas others are not. A physical theory is a model of physical events and cannot be proved from basic axioms. A physical theory is different from a mathematical theorem. Physical theories model reality and are a statement of what has been observed, and provide predictions of new observations.

Physical theories can become accepted if they are able to make correct predictions and avoid incorrect ones. All else being equal, physical theories which are simpler tend to be accepted over theories which are complex. Physical theories are also more likely to be accepted if they connect a wide range of phenomena. The process of testing a physical theory is part of the scientific method.

Theoretical physics is just one important part of physics; the other part is experimental physics. The difference between theoretical physics and mathematical physics is that mathematical physics finds the mathematical rigor required in mathematics to be more important than the contact with experiments and observations.

Mainstream theories

Mainstream theories (sometimes referred to as central theories) are the body of knowledge of both factual and scientific views and possess a usual scientific quality of the tests of repeatability, consistency with existing well-established science and experimentation.

Some examples of mainstream physical theories are:

• Classical mechanics
• Condensed matter physics
• Dynamics
• Electromagnetism
• Field theory
• Fluid dynamics
• General relativity
• Particle physics
• Quantum mechanics
• Quantum field theory
• Quantum electrochemistry
• Solid state physics and the electronic structure of materials
• Special relativity
• Standard Model
• Statistical mechanics
• Thermodynamics

Proposed theories

The proposed theories of physics are relatively new theories which deal with the study of physics which include scientific approaches, means for determining the validity of models and new types of reasoning used to arrive at the theory. Proposed theories can include fringe theories in the process of becoming established (and, sometimes, gaining wider acceptance). Proposed theories usually have not been tested.

Some examples of proposed physical theories are:

• Dynamic theory of gravity*
• Emergence
• Grand unification theory*
• Loop quantum gravity*
• M-theory
• Plasma Universe
• String theory
• Theory of everything*

Fringe theories

Fringe theories include any new area of scientific endeavor in the process of becoming established and some proposed theories. It can include speculative sciences. This includes physics fields and physical theories presented in accordance with known evidence, and a body of associated predictions have been made according to that theory.

Some fringe theories go on to become an widely accepted part of physics. Other fringe theories end up being disproven. Some fringe theories are a form of protoscience and others are a form of pseudoscience. The falsification of the original theory sometimes leads to reformulation of the theory.

Some examples of fringe physical theories are:

• Cold fusion*
• Dynamic theory of gravity*
• Grand unification theory*
• Loop quantum gravity*
• Luminiferous aether
• Orgone energy
• Steady state theory
• Theory of everything*

* These theories are both proposed and fringe theories.

See also

• List of theoretical physicists