I have just read the paper of Wilson et al. Nature 479, 376–379 (17 November 2011), which seems to be a remarkable step beyond the status of the research concerned with dynamic Casimir effect as outlined in Dodonov, Phys. Scripta 82, 038105 (2010).

Given the fact that each photon carries momentum, I wonder what the momentum balance of a system undergoing dynamic Casimir effect is like.

This seems to be a non-trivial issue, as Dalvit er al. http://arXiv.org/abs/1006.4790v2 (2010) show that such effect may lead to effective friction (out of 'nowhere', i.e. out of vacuum fluctuations). Indeed, this makes sense as it is only total (electromagnetic plus mechanical) momentum which is conserved.

But this raises also the following natural question: is dynamic Casimir effect a net source of mechanical momentum? To put it in more paradoxical words: does Nature allow us to build a propeller without propellant? Recent press reports (http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20140006052.pdf) seems to hint at that tantalizing direction. Just a fringe-science delusion?