In quantum mechanics, all the forces of nature are mediated by the exchange of particles such as photons, and these particles must obey this cosmic speed limit. So an action "here" can cause no effect "over there" any sooner than it would take light to travel there in a vacuum.
But two entangled particles can appear to influence one another instantaneously, whether they're in the same room or at opposite ends of the Universe.
Einstein called this ?spooky action at a distance' - spooky because there is no known mechanism for such an interaction, and because it would entail that things can be affected by events which, in some frame of reference, haven't happened yet.
Quantum entanglement occurs when two or more particles interact in a way that causes their fates to become linked: It becomes impossible to consider (or mathematically describe) each particle's condition independently of the others'. Collectively they constitute a single quantum state.
Austrian physicist Erwin Schrödinger in 1925 showed that if two particles are prepared in a quantum state such that there is a matching correlation between two ?canonically conjugate' dynamical quantities ? quantities like position and momentum whose values suffice to specify all the properties of a classical system ? then there are infinitely many dynamical quantities of the two particles for which there exist similar matching correlations: every function of the canonically conjugate pair of the first particle matches with the same function of the canonically conjugate pair of the second particle.
Thus system No. 1 ?does not only know these two answers but a vast number of others, and that with no mnemotechnical help whatsoever, at least with none that we know of.'