For example, if a spin-1/2 particle is said to be in the state | ↑ ↑ z ⟩ , a reference frame is implied, and it can be understood to be some reference frame with respect to an apparatus in a lab. It is obvious that the description of the particle does not place it in an absolute space, and doing so would make no sense at all because, as mentioned above, absolute space is empirically unobservable. On the other hand, if a magnetic field along y-axis is said to be given, the behaviour of the particle in such field can then be described. In this sense, y and z are just relative directions. They do not and need not have absolute meaning.