With WISE now on its way (a spectacular launch in the dark at Vandeberg Air Force Base), we now turn to the realm of exotica. Specifically, can we find ways to exploit the quantum vacuum to produce propulsion? I’ve seldom had such a flurry of interested emails than what followed the appearance of a paper by Alex Feigel, recently put up on the arXiv server. Feigel (Soreq Nuclear Research Center, Israel) discusses modifying the momentum of the quantum vacuum, an idea dear to that segment of the interstellar propulsion community that focuses on ‘propellantless’ propulsion.
Some background: Heisenberg’s uncertainty principle implies that it is impossible to achieve an absolute zero electromagnetic energy state in the vacuum of space. The measurement of the Casimir effect in 1997 demonstrated that a force would be exerted between two narrowly separated conducting plates. Indeed, at the micron scale, such plates are squeezed together as longer wavelength waves are excluded. The possibility of creating net propulsive forces using this energy was studied by NASA’s Breakthrough Propulsion Physics program during its all too brief lifetime at the agency.
A vacuum, then, is not free of energy, but seethes with electromagnetic waves coming into existence and popping back out of it again. We know these are measurable forces but what interests Feigel is the momentum associated with these electromagnetic fields. Learning how to manipulate that momentum could allow us to create a reaction we can use for propulsion. From the paper:
In this article we demonstrate that aggregating or rotating magneto-electric particles change[s] the momentum of [the] quantum vacuum and, as a consequence they acquire the resulting difference. It follows from momentum conservation: any change in momentum of zero fluctuations is compensated by a corresponding change in the momentum of a material object or electromagnetic field. These new occurrences of the vacuum momentum transfer do not require external means, such as previously proposed modification of the magneto-electric constant by applying external electric and magnetic fields or suppressing the quantum vacuum modes by cavity-imposed boundary conditions.
I don’t have the background to know whether what Feigel goes on to discuss is workable or not, but I do want to point you to the paper and the recent spate of comments on it. What I can do is farm Feigel’s work out to several Tau Zero practitioners whose expertise in the area of the quantum vacuum will allow them to make an informed judgment. Until then, let’s look at what Feigel says about what some are calling a ‘quantum propulsion machine.’
Feigel’s ‘magneto-electric quantum wheel’ would tap the forces in the quantum vacuum by introducing magneto-electric nanoparticles that would interact with them. Technology Review‘s physics arXiv blog discusses what Feigel is proposing:
The first method is to rapidly aggregate a number of magnetoelectric nanoparticles, a process which influences the boundary conditions for higher frequency electromagnetic waves, generating a force.
The second is simply to rotate a group of magnetoelectric nanoparticles, which also generates a Lorentz force.
Either way, the result is a change in velocity…
The magneto-electric quantum wheel would be what Feigel calls “…an addressable array of small magneto-electric particles or wires” which, upon rotation, would generate a force. Let me quote more fully from the paper:
…mechanical action of [the] quantum vacuum on magneto-electric objects may be observable and have a significant value. Rotation or self-assembly of the nanoparticles is enough to generate a back-action from zero electro-magnetic fluctuations. The amount of momentum that can be extracted from quantum vacuum by this effect may have in the future practical implications, depending on advances in magneto-electric materials.
The applications the author is talking about involve correcting the attitude of satellites in space. These are tiny effects, but the concept, which would involve propulsion that would occur without any loss of mass, is intriguing for that reason alone. Carrying propellant is a huge constraint as we look toward missions into deep space. Most of the vehicle is devoted to fuel tanks — consider Daedalus, or the ongoing Icarus project. Heck, consider Apollo, with its 600 to 1 mass ratio. Leaving the propellant at home is why concepts like Robert Forward’s lightsails can get to a star using known physics.
In the far future, what if we could harness the quantum vacuum to achieve significant propulsion without the huge mass ratio problem? We’re a long way from that, but if Feigel’s ideas are testable, let’s see where they may lead. I’ll hope to be posting further thoughts on this from Tau Zero practitioners soon. The paper is Feigel, “A magneto-electric quantum wheel,” available online.