Everything exists because particles follow rules, right? Every single particle is made up of smaller particles; these smaller particles may have different rules to the ones they create. Therefore, since we only need to simulate the set of rules for the particles on our level; atoms, a simulation is, in theory, possible. However, anomalies in the behaviour in atoms are caused by the particles that make the atoms acting normally, this cannot be simulated and so, a TRUE replica can never be made.