No-go theorem

In theoretical physics, a no-go theorem is a theorem that states that a particular situation is not physically possible. Specifically, the term describes results in quantum mechanics like Bell's theorem and the Kochen–Specker theorem that constrain the permissible types of hidden variable theories which try to explain the apparent randomness of quantum mechanics as a deterministic model featuring hidden states. Full descriptions of the no-go theorems named below are given in other articles linked to their names. A few of them are broad, general categories under which several theorems fall. Other names are broad and general-sounding but only refer to a single theorem. Antidynamo theorems is a general category of theorems that restrict the type of magnetic fields that can be produced by dynamo action. Cowling's theorem states that an axisymmetric magnetic field cannot be maintained through a self-sustaining dynamo action by an axially symmetric current. Earnshaw's theorem states that a collection of point charges cannot be maintained in a stable stationary equilibrium configuration solely by the electrostatic interaction of the charges. Bell's theorem Kochen–Specker theorem PBR theorem No-hiding theorem No-cloning theorem Quantum no-deleting theorem No-teleportation theorem No-broadcast theorem The no-communication theorem in quantum information theory gives conditions under which instantaneous transfer of information between two observers is impossible. No-programming theorem Weinberg–Witten theorem states that massless particles (either composite or elementary) with spin cannot carry a Lorentz-covariant current, while massless particles with spin cannot carry a Lorentz-covariant stress-energy. It is usually interpreted to mean that the graviton () in a relativistic quantum field theory cannot be a composite particle. Nielsen–Ninomiya theorem limits when it is possible to formulate a chiral lattice theory for fermions. Haag's theorem states that the interaction picture does not exist in an interacting, relativistic, quantum field theory (QFT).

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No-communication theorem

In physics, the no-communication theorem or no-signaling principle is a no-go theorem from quantum information theory which states that, during measurement of an entangled quantum state, it is not possible for one observer, by making a measurement of a subsystem of the total state, to communicate information to another observer. The theorem is important because, in quantum mechanics, quantum entanglement is an effect by which certain widely separated events can be correlated in ways that, at first glance, suggest the possibility of communication faster-than-light.

No-teleportation theorem

In quantum information theory, the no-teleportation theorem states that an arbitrary quantum state cannot be converted into a sequence of classical bits (or even an infinite number of such bits); nor can such bits be used to reconstruct the original state, thus "teleporting" it by merely moving classical bits around. Put another way, it states that the unit of quantum information, the qubit, cannot be exactly, precisely converted into classical information bits.

No-cloning theorem

In physics, the no-cloning theorem states that it is impossible to create an independent and identical copy of an arbitrary unknown quantum state, a statement which has profound implications in the field of quantum computing among others. The theorem is an evolution of the 1970 no-go theorem authored by James Park, in which he demonstrates that a non-disturbing measurement scheme which is both simple and perfect cannot exist (the same result would be independently derived in 1982 by Wootters and Zurek as well as Dieks the same year).

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