Graviton

A graviton is a hypothetical quantum of the gravitational field, often modeled as a massless spin-2 particle. No graviton has been observed.

Quantum field theory: A framework that describes particles as excitations of fields and their interactions through quantum laws. Gravitons are proposed as quanta of a field, following this framework’s particle-field picture.
Linearized gravity: An approximation to general relativity that treats weak gravitational fields as small perturbations of flat spacetime. Quantizing these perturbations yields the usual theoretical description of gravitons.
Graviton mass: The possible nonzero rest mass of a graviton, constrained by observations and theoretical consistency. A massive graviton would alter the standard massless proposal and could change gravity’s range.
Graviton detection: The experimental search for evidence that gravitational fields have discrete quantum excitations. No experiment has detected an individual graviton, and practical detection appears exceptionally difficult.
General relativity: Albert Einstein’s theory describing gravity as the curvature of spacetime caused by matter and energy. A graviton would provide a quantum description of gravity whose classical limit must recover this theory.
Massless particle: A particle with zero invariant mass that travels at the speed of light in vacuum. The conventional graviton is massless, consistent with gravity’s long range.
Newtonian gravity: A classical theory that describes gravity as an attractive force between masses, with an inverse-square law. It describes gravity without quantum particles, providing a familiar classical alternative.
Quantum gravity phenomenology: The study of observable consequences that could distinguish quantum-gravity theories. Potential signatures may test quantum gravity without directly detecting a single graviton.
Quantum gravity: The effort to formulate a theory that describes gravity using quantum principles. Gravitons arise in approaches that try to quantize gravity.
Helicity: The projection of a particle’s spin along its direction of motion. A massless spin-2 graviton has helicity states of +2 and −2.

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