In classical physics, all observables commute and the commutator would be zero. However this is not true in Quantum Mechanics, observables like position and momentum (time and frequency/energy) don't commute. Why? Is it because the (probability) wave functions/forms of position and momentum can never be both "squeezed" to high degree of accuracy at the same time? Is it because the particles are point particles and we are dealing with single dimensions? in QM and somehow they are telling us something fundamental when you get down to single dimensions. What does it mean not to commute? in QM/maths etc. What is the difference between variables/matrices that commute and those that don't? Do(es) time and space commute?