Historical research guide · 0604 · 2010
Progress in revolutionary propulsion physics
Marc G. Millis
In one minute
Marc Millis ran NASA’s Breakthrough Propulsion Physics project, and here, writing from the Tau Zero Foundation, he condenses the 739-page volume he and Eric Davis edited for the American Institute of Aeronautics and Astronautics into a single conference paper. Its subject is what physics would have to yield for a craft to move without carrying propellant, for interstellar distances to become traversable, and for an onboard energy source to match both. Millis sorts more than three dozen approaches by which of those three goals they address and how far each has travelled through the scientific method, and he is exact about where the field stands: the questions are now sharp, the make-or-break issues connect to named unsolved problems in physics, and no device is confirmed. He also hands the field a working method — judge a proposal by its rigour rather than by guessing at its feasibility, count reliable knowledge as success, publish the null results — and then lists the next experiments to run.
Connection
This is the paper chapter 1 borrows its evidence ladder from: Millis states, for a whole field at once, how to tell a rigorous claim from a loose one and what counts as progress when the breakthrough has not yet arrived. For chapters 4 and 13 it is the map — space drives, warp drives, wormholes, vacuum energy and the unfinished physics behind each, laid out with the specific next measurement attached to every one.
From the source
The three goals that organise the whole field, taken from the NASA Breakthrough Propulsion Physics project, are propulsion that needs no propellant, faster-than-light travel, and energy breakthroughs to power the first two; Millis itemises more than three dozen approaches against them, notes that none is at the stage of a confirmed working device, and grades each by how far it has moved through the scientific method.Sect. IV, Notional Propulsion Approaches; Table 1
A space drive — a craft that moves by interacting with the space around it instead of ejecting propellant — changes the arithmetic of a mission, because the energy required drops from an exponential function of trip velocity to a squared one; its two make-or-break issues are conservation of momentum and net external thrust.Sect. I, Introduction; Sect. IV, Space Drive Physics
The quantum vacuum is the leading candidate for the reaction medium such a drive would push against, and the size of the prize is exactly what is unsettled: depending on the factors chosen for the calculation, the equivalent mass density of quantum vacuum energy is quoted anywhere from 10 to the minus 26 up to 10 to the 98 kilograms per cubic metre, while the origin of inertial frames themselves remains undetermined.Sect. IV, Conservation of momentum; Sect. V, Unfinished Foundations of Physics
Comparing the two space-warping routes on energy, Millis reports that a wormhole is the cheaper one: roughly 10 to the 46 joules held below the ambient vacuum level — the paper’s term is negative energy — would open a faster-than-light wormhole about 100 metres across, whereas the same energy spent on a warp bubble of equal diameter buys only about one per cent of light speed.Sect. IV, Faster-Than-Light Implications of General Relativity, citing Frontiers of Propulsion Science p. 491
On drawing energy from the vacuum, the paper reports two established results and one open question: a net thrust from a dynamical Casimir effect has been shown theoretically, though that first embodiment is feebler than a photon rocket; energy conversion is possible in principle without violating thermodynamics, as in Forward’s Casimir battery, but as a one-shot device that must then be recharged; and whether the vacuum can be tapped continuously turns on whether it can be treated as a plenum, and on whether quantum electrodynamics or stochastic electrodynamics is the right formalism.Sect. IV, Quantum Vacuum, citing Frontiers of Propulsion Science Ch. 12 and p. 571, 577-587
The next-step list is specific and still open: use ultrahigh-intensity tabletop lasers to test the space-warping assertions of general relativity, independently repeat Tajmar’s anomalous frame-dragging near rotating cryogenics and Woodward’s inertia experiments, use micro- and nano-structure engineering to probe the quantum vacuum across many geometries and materials, run vacuum-energy experiments with negative-index and ultra-high carrier-density materials and superconductors, and publish null results so the community stops re-investing in dead ends.Sect. III, Novice Orientation; Sect. VI, Next Step Research
The way in
https://arxiv.org/abs/1101.1063How to cite it
Marc G. Millis (2010) Progress in revolutionary propulsion physics arXiv:1101.1063