# Tag Info

This is a bit of a negative answer, but consider instead an expectation of some other quantity, such as the energy: $$\langle E \rangle = \sum_i p_i E_i.$$ Now, it's obvious what $E_i$ means - it's the energy of state $i$ - but what does $p_iE_i$ mean? The answer is not very much really - it's the contribution of state $i$ to the expected energy, but it's ...