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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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particles with an intrinsic angular momentum (i.e. spin) equal to a "half integer" number of fundamental units: $\frac{(2n+1)}{2} \hbar$ for integer $n$. Fermions are required to be in a …
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A pictorial device which analyzes forces present on any body with the use of vectors. Allows easier grasping of problems involving either objects at equilibrium or in motion. Can be used to predict pr…
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Study of macroscopic and microscopic phenomena in chemical systems in terms of physical laws and concepts [thermodynamics, statistical mechanics, kinetic theory, quantum mechanics...].
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Polarization characterizes the oscillations in time the electromagnetic field is doing in the plane perpendicular to the propagation direction of a wave
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The systematic study of group representations, which describe abstract groups in terms of linear transformations of vector spaces, such that group elements or their generators are represented as matri…
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The historical development of physics concepts: who did what and when.
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"Faster-than-light", also known as superluminal velocities, refers to any sort of travel at a speed greater than the speed of light. Prohibited in mainstream physics due to the Special theory of …
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For questions about problems related to physics that involve evaluating integrals. Purely mathematical questions should be asked at math.SE.
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Circular motion about a central point or axis
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defined as the bending or flaring of light around the corners of an obstacle or aperture into the region of geometrical shadow of the obstacle. This flaring is consistent with the sprea…
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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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the quantum field theory believed to describe the strong nuclear force.
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Celestial body that orbits following an elliptical path around a star or stellar remnant.
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Dimensional analysis means to obtain results by analyzing the units in question, etc. DO NOT USE THIS TAG if your question is about degrees of freedom or spatial dimensions.
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The force on a body resulting from it's motion through a fluid (gas or liquid). This force is directly opposed to the direction of travel.
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a fundamental symmetry of [tag:special-relativity] describing the invariance of physics with respect to changes of orientation and boosts of inertial reference frames. These symmet…
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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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applies to questions that arise in graduate and post-secondary work. These questions often require domain-specific knowledge and could not be answered from a general source or …
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the practice of separating a signal by frequency (or sometimes energy or momentum) and analyzing the resulting spectrum.
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Matter not observed directly but inferred to exist based upon its gravitational effects.
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A nucleus made of protons and neutrons surrounded by a cloud of electrons equal in number to the protons.
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just because your question involves measurements (either quantum or classical). The measurement problem asks how wave function collapse occurs during measurement in quantum mechan…
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To be used for questions on geometry closely pertaining to physics. Includes differential geometry and euclidean geometry.
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any of several principles that find the physical trajectory of a system by minimizing or maximizing some value computed over the proposed path (for instance geometric optics can be reproduced by insis…
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a type of boundary such that any information past this boundary is inaccessible to the observer it is defined for. Common examples are the Schwarzschild radius of a black hole (whi…
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The time rate of change of energy
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relevant for computing that uses quantum states such as superposition and/or entanglement to locate low energy states as solutions to complex problems (rather than laborio…
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A mathematical construct quantifying the difference in effect of applying two operators in two alternate successions. It is the defining product of a Lie algebra, the efficient underlying description …
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Theory, lab and space experiments, and calculations related the physics of plasmas, i.e., matter constituted by ionized atoms.
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just because your question involves math! If your question is on simplification of a mathematical expression, please ask it at The mathematics tag covers non…
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Analogous to matter, but with charge of the particles opposite to their ordinary matter counterparts.
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light, uncharged leptons. The neutrino tag should be applied to question relating to neutrino properties or interactions involving neutrinos.
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vector valued functions which define a vector at each point in space. Examples of the vector field include the electric field and the velocity of a fluid.