An article has just appeared in WIRED about Woodward's theory. The author Daniel Oberhaus emailed me a couple of weeks ago asking my opinion of Woodward's work and he quotes me in the article as saying "In my opinion there is no merit to Woodward's theory". See this link for the article. This quote is a 'slight' truncation of what I said :) See his questions in bold, and my answers below:
Wired: How would you sum up your feelings about Jim's theory in a sentence or two? Is he crazy or is there merit to his ideas?
In my opinion there is no merit to Woodward's theory. It shares the problem of most of modern physics that it is constrained to work within the framework of general relativity so the derivation is complex and contrived and contains many unlikely assumptions and even some arbitrarily added factors, and yet it is still orders of magnitude away from predicting the Mach effect thrust it was intended to predict! The Mach Effect experiments are interesting but we have to consider the possibility that they are vibrational artefacts.
Wired: There's clearly a lot of skepticism around Jim's Mach effect theories. If you count yourself a skeptic, what don't you buy about this theory?
There are many theoretical problems with it, see eg Rodal 2019 and in going through the derivations you see that a lot of arbitrary factors are added in. However, my main reason for disregarding it is that it does not work. It fails to predict even the lab observations it was designed to explain - its predictions of observed thrust have been shown to be a factor of one thousand times out (eg: Mahood, 1999). I note that in the papers written about it the data is rarely compared with the observations directly.
Wired: What would it take to convince you that it was correct, if anything?
To convince me it would need a simply-derived non-arbitrary formula that predicts all the Mach Effect thrust experiments and a demonstration that the thrust varies as expected given the parameters in the theory, to rule out artefacts. So pretty much the opposite of what has happened so far.
Wired: Jim's been claiming to have produced propellantless propulsion for years. Do you think these results are real, or just noise / measurement error?
I think the experimental results are more interesting than the theory, but there is a significant possibility with vibrating solid objects that artefacts can occur (as seen with the Dean drive).
Wired: If not Mach effects, what do you think is a better explanation for what could be producing this apparent thrust? Why do you feel its a better explanation?
Vibrating objects have artefacts that can appear to be thrust. If the thrust is real then it does not seem to agree with the Woodward theory anyway. I have suggested the theory of quantised inertia (McCulloch, 2007) which predicts galaxy rotation without dark matter and predicts some, not all, of the Mach effect tests (McCulloch, 2018).
Rodal, J.A., 2019. A Machian wave effect in conformal, scalar–tensor gravitational theory. General Relativity and Gravitation, Volume 51, Article number: 64.
Mahood, T., 1999. Propellant-less propulsion: recent experimentla results exploiting transient mass modification. AIP Conf proc. STAIF-2000. AIP, 1014-20.
McCulloch, M.E., 2007. Modelling the Pioneer anomaly as modified inertia. MNRAS, 376(1), 338-342.
McCulloch, M.E., 2018. Propellant-less propulsion from quantised inertia. J Space Exploration, Volume: 7(3).