I saw this excerpt from the wikipedia article on EPR paradox They postulate that these elements of reality are, in modern terminology, local, in the sense that each belongs to a certain point in spacetime. Each element may, again in modern terminology, only be influenced by events which are loca...

In this question Can hydrogen atom exchange induce attractional forces between $e^-e^-$? one answer showed the range of exchange particle bt not how to calculate. how do we calculate/know what are range of exchange particle? Do we calculate or observe?

Newtonian mechanics seems to allow for both positive and negative gravitational mass as long as the inertial mass is always positive. The situation is analogous to electrostatics but with the opposite sign. Two positive masses or two negative masses are attracted to each other whereas one positi...

Let us consider a quantum mechanical system of interest S that interacts with the environment E. Then, the reduced density matrix $$ \hat \rho_\mathrm{S} = \mathrm{Tr}_\mathrm{E} \{ \hat \rho \} $$ is the partial trace over the environment, where $\hat \rho$ denotes the density matrix of the ...