# How come you can express the up and down spins

1. Aug 16, 2010

### dudy

I don't understand the following regarding spin:
1. How come you can express the up and down spins in any given direction, using the |+>,|-> in the z direction?
2. Why do I need two vectors (|->,|+>) to express a quantity that can only be either (1) or (-1) ?

2. Aug 16, 2010

### AJ Bentley

Last edited by a moderator: Apr 25, 2017