ABSTRACT
The starting point is the observation that the proton and neutron have masses very close to each other:
mn −mp mp
≃ 0.15 · 10−2 . (2.1)
Heisenberg interpreted this fact as a consequence of the invariance of the strong interaction Hamiltonian under transformations which change the states of the proton and neutron into arbitrary complex superpositions:(
p n
) → U
( p n
) (2.2)
where U is a unitary matrix, to preserve the normalisation |p|2 + |n|2. Every matrix of this type can be written as the product of a phase factor and a special matrix, i.e. a matrix with determinant equal to unity:
U = eiφUspec .
