Centauri Dreams has a review of the EMDrive by Marc Millis, former head of NASA’s Breakthrough Propulsion Physics project and founding architect of the Tau Zero Foundation and other experts. They have spent the last two months reviewing the relevant papers.
Millis enlisted the help of scientists with expertise in experimental issues, all of whom also contributed to BPP, and all of whom remain active in experimental work. The revisions and insertions of George Hathaway (Hathaway Consulting), Martin Tajmar (Dresden University), Eric Davis (EarthTech) and Jordan Maclay (Quantum Fields, LLC) have been discussed through frequent email exchanges as the final text began to emerge.
A peer-reviewed article about experimental tests of an EmDrive was just published in the AIAA Journal of Propulsion and Power by Harold (Sonny) White and colleagues: White, H., March, P., Lawrence, J., Vera, J., Sylvester, A., Brady, D., & Bailey, P. (2016), “Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum,” Journal of Propulsion and Power, (print version pending, online version here.
That new article, plus related peer-reviewed articles, were reviewed by colleagues in the Tau Zero network, including two who operate similar low-thrust propulsion tests stands. From our reviews and discussions, they have reached the following professional opinions – summarized in the list below and then detailed in the body of this article. They regret that they can only offer opinions instead of definitive conclusions. That ambiguity is a significant part of this story that also merits discussion.
The overview material are shown here but the original overview and the details are at the Centauri Dreams article.
This article will also reproduce the details looking at Space drive theories.
(1) The experimental methods and resulting data indicate a possible new force-producing effect, but not yet satisfying the threshold of “extraordinary evidence for extraordinary claims” – especially since this is a measurement of small effects.
(2) The propulsion physics explanations offered, which already assume that the measured force is real, are not sound.
(3) Experiments have been conducted on other anomalous forces, whose fidelity and implications merit comparable scrutiny, specifically Jim Woodward’s “Mach Effect Thruster.”
(1) If either the EmDrive or Mach Effect Thrusters are indeed genuine, then new physics is being discovered – the ramifications of which cannot be assessed until after those effects are sufficiently modeled. Even if it turns out that the effects are of minor utility, having new experimental approaches to explore unfinished physics would be valuable.
(2) Even if genuine, it is premature to assess the potential utility of these devices. Existing data only addresses some of the characteristics necessary to compare with other technologies. At this point, it is best to withhold judgment, either pro or con.
Pitfalls to Avoid
(1) The earlier repeated tactic, to attempt fast and cheap experimental tests, has turned out to be neither fast nor cheap. It’s been at least 14 years since the EmDrive first emerged (2002) and despite numerous tests, we still lack a definitive conclusion.
(2) In much the same way that thermal and chamber effects are obscuring the force measurements, our ability to reach accurate conclusions is impeded by our natural human behavior of jumping to conclusions, confirmation biases, sensationalism, and pedantic reflexes. This is part of the reality that also needs understanding so that we can separate those influences from the underlying physics.
(1) Continue scrutinizing the existing experimental investigations on both the EmDrive and Mach Effect Thrusters.
(2) To break the cycle of endlessly not doing the right things to get a definitive answer, begin a more in-depth experimental program using qualified and impartial labs, plus qualified and impartial analysts. The Tau Zero Foundation stands ready to make arrangements with suitable labs and analysts to produce reliable findings, pro or con.
(3) If it turns out that the effects are genuine, then continue with separate (a) engineering and (b) physics research, where the engineers focus on creating viable devices and the physicists focus on deciphering nature. In both cases:
Characterize the parameters that affect the effects.
Deduce mathematical models.
Apply those models to (a) assess scalability to practical levels, and (b) understand the new phenomena and its relation to other fundamental physics.
On all of the above, conduct and publish the research with a focus on the reliability of the findings rather than on their implications.
EmDrive and Other Space Drive Theories
First, I cannot stress enough that there is no new EmDrive “effect” yet about which to theorize. The physical evidence on the EmDrive is neither defensible nor does it include enough operating parameters to characterize a new effect. The data is not even reliable enough to deduce the force-per-power relationship, let alone any other important correlations. What about the effects of changing the dimensions or geometry, changing the materials, or changing the microwave frequencies or modulation? And then there is the unanswered question, what are the propulsion forces pushing on?
Assuming for the moment that the EmDrive is a new force-producing effect, we know at least two things (1) it is not a photon rocket, because the claimed forces are 360 times greater than the photon rocket effect, and (2) a force, without an “equal and opposite force,” goes beyond Newton’s laws. Note that I did not evoke the more familiar “violating conservation of momentum” point. That is because these experiments are still trying to figure out if there is a force. We won’t get to conservation of momentum until after those forces are applied to accelerate an object. If that happens, then we must ask what reaction mass is being accelerated in the opposite direction. If the effects are indeed genuine, then new physics is being discovered or old physics is being applied in a new, unfamiliar context.
For those claiming to have a theory to predict a new propulsion effect, it is necessary that those theories make testable numeric predictions. The predictions in Juan’s 2013 paper did not match its results. The analytical discussions in White’s 2016 experimental paper do not make theoretical predictions. The same is true with his 2015 theoretical paper: White (2015), “A discussion on characteristics of the quantum vacuum,” Physics Essays, vol. 28, no. 4, 496-502.
Short of having a self-consistent theory, any speculations should at least accurately echo the physics they cite. The explanations in the White’s 2016 experimental paper, White’s 2015 theory paper, and even White’s 2013 report on the self-named “White-Juday Warp Field Interferometer” (White (2013), “Warp Field Mechanics 101,” Journal of the British Interplanetary Society, vol. 66, pp. 242-247), did not pass this threshold. I’ll leave to other authors to elaborate on the 2015 and 2016 papers, while a review of the 2013 warp drive claims is available here. It is Lee & Cleaver (2014), “The Inability of the White-Juday Warp Field Interferometer to Spectrally Resolve Spacetime Distortions,” [physics.gen-ph].
In contrast, it is also important to avoid pedantic reflexes – summarily dismissing anything that does not fit what we already know, or assuming all of our existing theories are completely correct. For example, the observations that lead to the Dark Matter and Dark Energy hypotheses do not match existing theories, but that evidence has been reliably documented. Using that data, many different theories are being hypothesized and tested. The distinction here is that both the proponents and challengers make sure they are accurately representing what is, and is not yet, known.
If a propulsion physics breakthrough is to be found, it will likely be discovered by examining relevant open questions in physics. A relevant theoretical question to non-rocket propulsion concepts (including the EmDrive) is ensuring conservation of momentum. One way to approach this is to look for phenomena is space that might serve as a reaction mass in lieu of propellant, perhaps like the quantum vacuum. Another approach is to dig deeper into the nature of inertial frames. Inertial frames are the reference frames upon which the laws of motion and the conservation laws are defined, yet it is still unknown what causes inertial frames to exist or if they have any deeper properties that might prove useful.
Woodward Tests and Theory
In addition to the overtly touted EmDrive, there are about two-dozen other space drive concepts of varying degree of substance. One of them started out as a theoretical investigation into the physics of inertial frames which then advanced to make testable numeric predictions. Specifically I’m referring to what is now called the “Mach Effect Thruster” concept of James F. Woodward, which dates back at least to this article:
Woodward, James F. (1990), “A new experimental approach to Mach’s principle and relativistic gravitation,” Foundations of Physics Letters, vol. 3, no. 5, pp. 497-506.
A more in-depth and recent publication on these concepts is available as:
Woodward, James F. (2013) Making Starships and Stargates: The Science of Interstellar Transport and Absurdly Benign Wormholes. Springer Praxis Books.
Experiments have been modestly underway for years, including three recent independent replication attempts by George Hathaway in Toronto Canada, Martin Tajmar in Dresden Germany, and Nembo Buldrini in Wiener Neustadt, Austria. Those two first labs are also testing the EmDrive, but no journal publications of those results are out yet. A workshop was held to review these findings in September 20-23, 2016, in Estes Park, Colorado. I understand from an email conversation with Jim Woodward that these reports and workshop proceedings are now undergoing peer review for likely publication early in 2017.
The main point here, by citing just this one other example, is that there are other approaches beyond the highly publicized EmDrive claims. It would be a disservice to our readers to let a media fixation with one theme blind us to alternatives.
If either the EmDrive or Mach Effect Thruster is indeed genuine, then new physics is being discovered or old physics is being applied in a new, unfamiliar context. Either would be profound. Today it is premature to assert than any of these effects are genuine, or conversely, to flatly rule out that such propulsion ambitions are impossible.