The Current Status of the “Anomalous Thrust” Results

There is a recent paper from the NASA / JSC “Eagle Works” that discusses “anomalous thrust” from various sorts of drives that (to be blunt) violate at least the conservation of linear momentum. These have gotten some breathless reports in the press (Nasa validates ‘impossible’ space drive
) and also the inevitable push back (How to fool the world with bad science)

I thought that the “bad science” take was pretty appropriate when all we had to go on was the conference abstract. Now, however, the full paper, Anomalous Thrust Production… (still not peer reviewed), is out, and it is much better. I still think it is wrong, but I do not think it is bad science, and it will, in my opinion, have to be refuted experimentally.


The “null thruster” in the abstract (which showed about the same effect as the test thruster) is something of a red herring. Reading the paper, they have a true “null load,” which shows no thrust, while the “null thruster” was a modification of a Cannae drive that was not supposed to produce thrust in the Cannae drive theory, and so this was more of a test of drive theory than the experimental setup. In any event, they tested several types of drives, and so weren’t dependent on the Cannae theory overall.

They did pretty much all of the things you would like to see as experimental checks, at least on a first read (such as reversing the direction and making sure the thrust reverses).

They seem to have done a thoughtful and careful job, including testing in vacuum and documenting what they were doing.

So, I still think they are likely wrong, but this ups the ante. In my opinion, you can’t just say “this is obviously wrong.” I bet there will be a bunch of attempts to replicate it in labs all over the place.

I find the theories here (and I have now read several in some depth) to be bad, either wrong, or handwavy, or both*. I would discount them entirely. In the unlikely event that this effect is real (and I mean, some non-standard physics effect), then the theory is likely to be something different than any of the proposals, The experiment’s the thing, and the game now has to be disproving the Eagleworks results. Only once a bunch of people have failed to do that (or one person has done it) is there much else to say.

* On pushing on virtual particles or quantum spacetime or whatever. These are 1 GHz photons, more or less. Such pushing would cause a _vacuum_ dispersion. Vacuum dispersion limits are set by timing of high energy photons from Gamma Ray Bursts across cosmic distances. These tests use ~ 100 MeV photons over ~10^10 light years, and so are many orders of magnitude tighter than the NASA Eagle Works results. This in my opinion rules out any photon – vacuum interaction as the cause of these anomalous thrusts.


Franson’s speed of light correction disagrees with solar system tests

The Physics arXiv blog has an article entitled “Evidence of a Correction To the Speed of Light” which has gotten some attention (incuding mine). This article is based on a paper “Apparent correction to the speed of light in a gravitational potential”, by J.D. Franson, so I thought I would look at the original paper. Having done so, I just wanted to note here that I think this theory is not valid as it seems to be in disagreement with Solar System tests of General Relativity.

For a reference for such tests, I will use Clifford Will’s paper “The Confrontation between General Relativity and Experiment” in the Living Reviews of Relativity (specifically, the 11 June 2014 version, which I will refer to as Will, 2014).

Franson’s paper can be boiled down to his Equation 18, which predicts a change in the gravitational red shift by a factor of \frac{9 \alpha}{64} for photons, where \alpha is the fine structure constant (\sim 1/137), so the total correction is \sim 1.08 \times 10^{-2}. He claims this correction does not apply to neutrinos, thus providing an observable effect with Supernova 1987A. (I am not sure I agree with that conclusion but that point doesn’t matter for this note.) In his theory Equation 18 does apply to (low energy) photons, and so actually represents a change of the “the speed of light c as measured in a global reference frame,” which is his way of describing the gravitational red shift (see Equation 1). In other words, he predicts a 1% change in the gravitational red shift for low energy photons (where low energy is << 511 KeV, i.e., visible light, radio waves, etc.); this effect can be directly tested without depending on neutrino generating Supernova. In the low energy limit, the correction does not depend on the photon wavelength, and so radio observations should exhibit it too.

The gravitational red shift has indeed been tested, by a NASA experiment called Gravity Probe A, with an accuracy of a few parts in 10^-4 (see Figure 3 in WIll, 2014). This excludes the Franson correction, but it does not measure directly the apparent speed of photons. Since the Shapiro delay (the time delay of photons passing through a gravitational potential) also depends on the gravitational redshift, Franson's theory thus predicts a 1% change in that too, and that does depend on the motion of photons. Solar system measurements of the Shapiro delay provide estimates of the so called PPN \gamma parameter, which is the ratio of the observed effect with that predicted by General Relativity (so that Franson is effectively predicting a \gamma of ~ 0.989). This effect is much too large to be consistent with experiment (see Figure 5 in Will, 2014). Even the Viking relativity test I worked on with Irwin Shapiro in the 1970’s and 80’s (which had a relative error on PPN \gamma of ~ 0.001) was good enough to rule out the Franson hypothesis.

So my conclusion is that the theory is simply wrong, and I don’t see any easy out for it. The Shapiro delay tests in the Solar System are particularly compelling, as they are based on photons moving in a gravitational potential, specifically the condition Franson’s Equation 18 is intended to address.