This information together with the detected position of the neutron is used to construct the momentum vector of the neutrons.

The physics of twisting can be explained by looking at the components of the angular momentum vector.

The direction of the angular momentum vector will not change unless a net torque is applied to the system.

The state vectors ( and ) can be easily used to compute the angular momentum vector as .

Since the momentum vectors are the same magnitude, but opposite direction, they add to zero.

But with each encounter, the direction of the angular momentum vector is changed slightly.

These conservation laws are equivalent to two constraints to the three-dimensional angular momentum vector .

This is perpendicular to its angular momentum vector.

In the theory of relativity, this momentum vector is taken as the four-momentum.

Find any set where the momentum vectors add to zero and you have such a case.