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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Any of the various explanations of gravity as a quantum theory, including string theory and loop quantum gravity.
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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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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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for questions seeking a single specific paper or a short, non-open-ended list of references, like "What paper first discovered X?", "Where can I find the original derivation of X?", or "W…
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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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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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Applies also to pre-Hilbert spaces, rigged Hilbert spaces, and spaces with negative norm or zero-norm states.
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The time rate of change of the position of an object
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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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A fundamental property of matter which causes it to experience electromagnetic forces.
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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 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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Geometric object with magnitude (length) and direction.
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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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A measure of the rate at which electric charge is transported (especially through a circuit), it has units of charge/time.
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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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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 cosmological phenomenon wherein the proper distance between two spatial points for a given inertial reference frame increases from one moment of time to another. That is, space it…
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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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the planet on which we live, the 3rd planet from the Sun. Questions using this tag should be about Earth the planet and not Earth-like planets nor earth, as in dirt or soil.
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for Heisenberg quantum mechanical uncertainty principle.
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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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Interaction between two or more bodies that results in physical contact and an exchange of momentum between the bodies involved.
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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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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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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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The union of special (SR) and general (GR) relativity. Use this tag if both SR and GR apply.
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The product of the force on an object and the displacement the object undergoes along the direction of the force.
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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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standards of measurement used for different types of quantities.