: Lau: So if there are two fermions of different kind they can have the same quantum state??

Yes, that's right as long as they are distinguishable in terms of the interaction with the fields involved. For instance, even though the proton and neutron are distinguishable in terms of their interaction with electromagnetic field, in nucleons they still tend to combine in an anti-symmetric way consistent with the pauli exclusion principle because they are fermions and the dominant field at that level is the strong force which doesn't interact with electric charge so in terms of their interaction with the dominant field they are indistinguishable. An example that the pauli exclusion principle does not apply to bosons is a Bose-Einstein condensate. The bosons all enter the same ground state. In such a state you can't determine that boson A is at this coordinate and B is at that coordinate as their wave functions overlap or more accurately combine symmetrically into one single quantum state.

: Lau: I know fermions have spin number in 'halves' and bosons have integral spin. what is spin actually refers to?(I mean in calculation) Is it related to the angular veocity? or angular momentum? or what??

Angular momentum is correct.

• Re: astrophysics - Lau,_symmetry_is_beautiful/">Lau, symmetry is beautiful - December 2, 1999 - 13:17 UTC
  • Re: astrophysics - Zephram_Cochrane/">Zephram Cochrane - December 2, 1999 - 15:33 UTC