Fell's theorem


Measure and probability theory


algebraic quantum field theory (perturbative, on curved spacetimes, homotopical)


field theory: classical, pre-quantum, quantum, perturbative quantum

Lagrangian field theory


quantum mechanical system

free field quantization

gauge theories

interacting field quantization


States and observables

Operator algebra

Local QFT

Perturbative QFT


physics, mathematical physics, philosophy of physics

Surveys, textbooks and lecture notes

theory (physics), model (physics)

experiment, measurement, computable physics



Fell’s theorem is about a property of vector states of a C-star algebra, it says that if the kernels of two representations of the algebra coincide, then the vector states are mutually weak-* dense. This has a profound consequence for the AQFT interpretation: A state represents the physical state of a physical system. Since one can always only perform a finite number of measurements, with a finite precision, it is only possible to determine a weak-* neigborhood of a given state. This means that it is not possible - not even in principle - to distinguish representations with coinciding kernels by measurements.

For this reason representations with coinciding kernels are sometimes called physically equivalent in the AQFT literature.


Let A be a unital C *C^*-algebra and π 1,π 2\pi_1, \pi_2 be two representations of A on a Hilbert space H.


equivalence theorem Every vector state of π 1\pi_1 is the weak-* limit of vector states of π 2\pi_2 iff the kernel of π 1\pi_1 contains the kernel of π 2\pi_2.

Other theorems about the foundations and interpretation of quantum mechanics include:


Revised on December 11, 2017 08:45:29 by Urs Schreiber (