so causality is violated unobservable becuase we cant measure virtual particles? my friend said "While virtual particles can break causality, we can never observe virtual particles, and so we never can observe causality violations. What is a virtual particle? Virtual particles are how we understand that quantum interactions occur. For example, suppose two electrons come along and bump off of each other. One electron experiences the electric field of the other electron. The force between the two electrons is due to exchange of photons. These photons are virtual.
Given this, the influence of one electron on another is the result of a sum over all of the virtual photons exchanged---this is the Feynman path integral. While some virtual photons travel faster than the speed of light, some (in fact, many more) photons also travel slower than the speed of light. This means that the net effect is mediated at a speed that respects causality.
Summary: While one photon in the interaction may travel faster than the speed of light, the net effect of the interaction requires that one sum over all photons exchanged. Because the probability of a virtual photon traveling slower than the speed of light is MUCH greater than the probability of a virtual photon traveling faster than the speed of light, the net effect means that the information between the two electrons is exchanged in a manner which respects causality''