Can the quantum vacuum be used as a reaction medium to generate thrust?
  A number of recent controversial experiments have observed anomalous thrust forces with devices making use of electromagnetic fields, and which do not appear to emit any particles or radiation; in apparent violation of the principle of the conservation of momentum. This has led to proposals that the measured forces are being produced due to an interaction between the applied electromagnetic fields of the device, and virtual particles/anti-particles of the quantum vacuum. Using an argument based on Lorentz invariance, as well as a formal quantum field theoretic calculation, we investigate the feasibility of these proposals. We find that both the vacuum expectation value of the linear momentum operator (the zero-point momentum), as well as the conserved current, are both exactly zero; the quantum vacuum does not appear to be a viable reaction medium with which to generate thrust. 
Trevor Lafleur
quant-ph