For those of you who don’t see Spaceflight, a magazine published by the British Interplanetary Society, it may be useful to know that an article by Richard Obousy and Gerald Cleaver (Baylor University) on warp drive theory from the April issue is now available on the arXiv server. This material was presented at the November, 2007 symposium held by the BIS in London. Kelvin Long, who organized the session, had earlier passed along several documents from the proceedings that we looked at here, and also wrote up the duo’s ideas in the same issue of Spaceflight.
But let’s backtrack a minute to Miguel Alcubierre’s 1994 paper, which demonstrated that it would be possible — within the context of General Relativity — to envision a space drive that could get you to your destination in a time shorter than it would take light itself to get there. Contracting space in front of the craft while inflating it behind, the drive is permissible because the starship itself would not be going faster than light. Rather, the space around it would be moving in such a way as to make the trip possible.
And that’s the key — the speed of light stricture does not apply to spacetime itself. Can we learn how to generate a region of expanding spacetime and one of contracting spacetime? Obousy and Cleaver argue that nature can offer insights, for spacetime itself is already expanding, a fact we realized with the work of Edwin Hubble in 1929 and have been wrestling with in various ways ever since. A warp drive would demand that the slow expansion of space that we observe be made to function extremely quickly, which makes understanding the cosmological constant the key demand of any attempt to build a true warp drive.
Now we’re truly in deep water, for attempts to explain the cosmological constant using quantum field theory have been shown to be off by a factor of 10120, an obvious marker of how far from descriptive current explanations are. The authors then turn to supersymmetry — the theory that all particles have an associated superparticle with a differing spin — to explore the question. And in rapid order they consider the cosmological constant in terms of higher dimensions, relating these first to the work of Theodore Kaluza, who suggested a fifth dimension in 1919, and then in ongoing efforts to explore extra dimensions using string theory.
Thus a potential scenario for an Alcubierre-style warp drive emerges:
In a recent paper, we addressed the plausibility of locally inﬂuencing the size of the extra dimension to locally (by local, we mean in the vicinity of a spacecraft) adjust the cosmological constant. This could theoretically create a modiﬁcation of spacetime around a craft that could be tuned to acquire the characteristics of the Alcubierre bubble… The basic idea is that by altering the radius of an extra dimension, it would be possible, in principle, to adjust the energy density of spacetime (which relates directly to the cosmological constant which ultimately controls the inﬂation/contraction of space itself). We have taken two approaches to this concept: one from the viewpoint of QFT another from GR. The equations of both theories indicated that the physics of the extra
dimensional space eﬀects the expansion rate of ‘normal’ space by a ‘dimensional shearing’ eﬀect. The equations of GR demonstrated that shrinking the extra dimension would inﬂate our space, and that expanding the extra dimension would contract our space. In this way, a bubble of expanding/contracting spacetime could be created at the rear/front of a spacecraft.
How fast might a warp-driven spacecraft go? Obousy and Cleaver work out an upper limit on such a velocity (based upon quantum field theory) of 1032 c, c being the speed of light. Mind boggling to be sure, but tempered by the fact that the energy required for such a velocity is significantly greater than that available in the observable universe. Another of those ‘small problems of engineering,’ as Robert Forward used to call them…
Clearly, we’re up against huge hurdles, many of them suggested by this paper. Will we validate the idea of supersymmetry in the near future? Will some variant of string theory be subjected to experimental analysis, and if so, how? What sort of engineering would actually contribute to manipulating an extra dimension even if we were able to find one? No, I wouldn’t expect a warp drive breakthrough any time soon, but laying a theoretical basis for a technology has to be step one. That means parsing the issues and identifying potential solutions, some of which may be investigated and perhaps demonstrated in subsequent experiments.
The paper is Obousy and Cleaver, “Putting the ‘Warp’ into Warp Drive,” Spaceflight, Vol 50, No.4, April 2008, pp. 149-151 (available online).