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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In fluid dynamics, potential flow describes the velocity field as the gradient of a scalar function: the velocity potential.
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The time rate of change of energy
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Force per unit area.
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For questions about probability, probability theory, probability distributions, expected values and related matters. Purely mathematical questions should be asked on Math.SE.
A proposed replacement for the "soft-question" tag, since many of those questions are off-topic. See http://meta.physics.stackexchange.com/q/7551/44126
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Object moving through space due to the exertion of a force.
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propagator gives the probability amplitude for a particle to travel from one place to another in a given time, or to travel with a certain energy and momentum.
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a positively charged particle which is generally considered to be a composite particle comprising of three quarks interacting through the strong force (e.g. in the standard model.)
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a hypothetical form of radioactive decay in which the proton decays into lighter subatomic particles. There is currently no experimental evidence that proton decay.
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Quantum field theory (QFT) in curved spacetime is a field of study that focuses on problems that arise when considering a quantum field on a fixed, curved spacetime.
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Quantization refers to the procedure or methodology for replacing a classical system by a quantum system. If the question is about the quantized or discrete behavior of a phenomenon use the [tag:discr…
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for anomalies in a symmetry, either in classical or quantum theories. DO NOT USE THIS TAG for anomalies in a measurement.
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the quantum field theory believed to describe the strong nuclear force.
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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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the theoretical framework describing the quantisation of classical fields which allows a Lorentz-invariant formulation of quantum mechanics. QFT is used both in high ener…
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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 study of the informational content of quantum states. The most common object of study is the "qubit", the information in a two-state quantum system such as spin-1/2 or photo…
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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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Quantum mechanics describes the microscopic properties of nature in a regime where classical mechanics no longer applies. It explains phenomena such as the wave-particle duality, quantization of energ…
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A research field within general optical physics concerned with light and its material interaction: where light is modelled by full quantum mechanical description.
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Fundamental characteristic property of particles which together with orbital angular momentum acts as the generator of rotations and which doesn't have a classical equivalent but is sometimes compared…