- #1
smallphi
- 441
- 2
Correct me if wrong, but in non-relativistic QM, the Hilbert space of two interacting spins is spanned by the tensor product of non-interacting states (the so called spin-addition). For addition of two 1/2 spins for example:
|1,1> = |+>|+>
|1,0> = (|+>|-> + |->|+>) / sqrt(2)
|1,-1> = |->|->
|0,0> = (|+>|-> - |->|+>) / sqrt(2)
Now, why the Fock space of the interacting theory in QFT can't be spanned by the non-interacting states i.e. why the interaction and non-interaction Fock spaces are not the same?
|1,1> = |+>|+>
|1,0> = (|+>|-> + |->|+>) / sqrt(2)
|1,-1> = |->|->
|0,0> = (|+>|-> - |->|+>) / sqrt(2)
Now, why the Fock space of the interacting theory in QFT can't be spanned by the non-interacting states i.e. why the interaction and non-interaction Fock spaces are not the same?