4 ms·
This is not correct. The expectation value of the angular momentum along the x-axis might be zero, but the state itself simply does not have a definite angular
by prof-dr-ir 4y ago
This is not correct. The expectation value of the angular momentum along the x-axis might be zero, but the state itself simply does not have a definite angular momentum.
I like your example because it clearly shows the subtlety that the original comment by rssoconnor also misses. Energy, momentum, and angular momentum absolutely are conserved quantities. But if you prepare your initial state such that it does not have a definite value of these quantities then you cannot with certainty predict the measured value, either.
- kgwgk 4y agoGood point. Anyway, the original example reduces to this. After the first measurement [it doesn’t really matter which one is considered as first] we have a couple of complementary states +/- for the measured axis but it’s not well defined for other directions and in general a second measurement will break the symmetry.
- JBits 4y agoWhat makes these quantities conserved in QM/QFT?