Then the transition probability per unit time is given by . This is Fermi's golden rule . The variational method Consider an arbitrary physical system with a time-independent Hamiltonian. Let E 0 denote the energy of the ground state. The minimal value thus obtained constitutes an approximation to the ground state energy E 0 of the system.
Every elementary particle is either a fermion or a boson .
A state of many identical particles is totally antisymmetric with respect to the interchange of any two particles if they are fermions, and it is totally symmetric if they are bosons. No two identical fermions can have exactly the same set of quantum numbers.