A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.

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Use this for questions relating to the proper use of physics terminology or nomenclature.
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A gauge theory has internal degrees of freedom that do not affect the foretold physical outcomes of the theory. The theory has a Lie group of *continuous symmetries* of these internal degrees of freed…
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energy transferred from one system to another by thermal interaction. In contrast to work, heat is always accompanied by a transfer of entropy. Heat flow is characteristic of macroscopic objec…
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physics taught and learned. Teaching strategies, class examples and demonstrations; learning resources, career advice, etc. For explicit problems, use the 'homework' tag instead.
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the quantum field theory believed to describe the electromagnetic interaction (and with some extension the weak nuclear force).
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an ensemble of techniques which serves to treat the infinities which appear in quantum field theory or statistical mechanics.
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a process in which energetic particles or energetic waves travel through a medium or space. The particles or waves radiate (i.e., travel outward in all directions) from a source.
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a general term for several physical processes in which radiation of some sort changes direction due to an interaction with a particle. Scattering can be classified by the type of radiati…
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a formalism in Classical Mechanics. Besides Lagrangian Mechanics, it is an effective way of reformulating classical mechanics in a simple way. Very useful in Quantum Mecha…
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The time rate of change of the position of an object
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Applies also to pre-Hilbert spaces, rigged Hilbert spaces, and spaces with negative norm or zero-norm states.
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A fundamental property of matter which causes it to experience electromagnetic forces.
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the mechanism by which quantum correlations between two sub-systems survive even after being physically separated from an interaction region. The correlations could in principl…
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used to describe any system with a "linear" restoring force that tends to return the system to a equilibrium state. There is both a classical harmonic oscillator and …
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The study of how the properties of matter arise from its structure at all scales and of how processing can be used to modify those properties (often in pursuit of a specific application).
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the field of physics that studies atoms as an isolated system of electrons and an atomic nucleus. It is primarily concerned with the arrangement of electrons around the nucleus and t…
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for Heisenberg quantum mechanical uncertainty principle.
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for questions relating to what, if anything, the quantum mechanical formalism and experimental results say about the way the world works.
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Geometric object with magnitude (length) and direction.
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According to the current cosmological theories, it's the model that explains the early life of the universe, starting from a rapid expansion of hot and dense matter.
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The result of sampling the property of a system
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The historical development of physics concepts: who did what and when.
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The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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The near-vacuum extending between the planets and stars, containing small amounts of gas and dust. Also called outer space to refer to the physical universe beyond the Earth's atmosphere.
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the branch of solid state physics that focuses on specific properties of semiconductors. It studies dynamics of different perturbations (mainly electrons and holes) in the sem…
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a branch of abstract algebra. A group is a set of objects, together with a binary operation, that satisfies four axioms. The set must be closed under the operation and contain an ident…
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Interaction between two or more bodies that results in physical contact and an exchange of momentum between the bodies involved.
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standards of measurement used for different types of quantities.