Science isn’t easy. It isn’t supposed to be. The process of open publication, peer review and clear data are a part of science because they help us understand how the Universe works. It can be inconvenient and contentious, but it works. Through this process, new ideas are faced with an uphill battle. This is particularly true of ideas that would contradict the foundational theories of physics. So it’s tempting to react to such opposition by playing a different game. Rather than addressing criticism, you start building a story where your idea is obviously right, and others are simply too closed-minded to see it. Down that path lies pseudoscience, and sometimes you can watch it happening. Take for example, Mike McCulloch‘s theory of Modified inertia by a Hubble-scale Casimir effect (MiHsC), also known as quantized inertia.

McCulloch’s model has been in the works since 2008, but it has become popular in recent years due to its connection to the EMDrive. You might recall this as the device that (according to its proponents) can create a thrust without any traditional propellant which could revolutionize space travel and take us to the stars. The EMDrive has created quite a stir among the general public because of the tremendous possibilities if it succeeds. Meanwhile, scientists have noted that even the best experimental results can’t be distinguished from background noise, and that such a device would violate basic physics. McCulloch argued that the effect was not only real, but that it could be explained in the context of his model.

The basic idea of MiHsC is that inertia is caused by Unruh radiation. Inertia is a basic property of matter, and means that the velocity of an object will remain constant unless a force acts on it. It is the basis of Newton’s first law of motion. Unruh radiation has never been observed, but it appears in quantum physics. In quantum theory, empty space can be described as being filled with a quantum field. A vacuum, in this view, is simply the lowest possible energy state for these fields. In most cases empty space looks like a vacuum as we’d expect, but for an accelerating observer the field has an observed energy. As a result, an accelerating observer would be heated by quantum particles known as Unruh radiation. McCulloch argues that when an object accelerates it interacts with Unruh radiation, which causes the object to resist a change of motion. Thus inertia is an effect of acceleration rather than an inherent property of matter.

There are problems with this idea from the get-go. For one thing, the Unruh effect in standard quantum theory is extraordinarily small. If you accelerated a trillion times greater than Earth gravity, you’d only see a thermal temperature of 40 billionths of a degree above absolute zero. Furthermore, since Unruh radiation comes from all directions, it couldn’t create the effects of inertia on its own. But rather than be deterred by this, McCulloch adds other effects into the mix. Since the observable universe is finite, the wavelengths of Unruh radiation is limited, and combined with a cosmic Casimir effect and a bit of information theory, can somehow produce the effect of inertia. The Unruh effect, Casimir effect and information theory are all well established in modern physics, but their hodge-podge combination in MiHsC is misapplied.

Credit: EM Drive prototype by NASA/Eagleworks, via NASA Spaceflight Forum.

However even this isn’t enough to explain the EMDrive. In his paper on the EMDrive, McCulloch argued that photons have mass, and that photon mass varies with time. The time-varying inertia allows the EMDrive accelerate. The idea not only violates Newton’s third law of motion, it violates special relativity, general relativity and Noether’s theorem. Since these are each well tested theories that form the basis of countless other theories, their violation would completely overturn all of modern physics. It’s no wonder most scientists have been aggressively skeptical of the idea. This criticism could be overcome by working out the specific details of  MiHsC, clearly addressing these kinds of problems. But that would be extremely difficult given just how strongly verified these theories are. The alternative is to double down, count the EMDrive as a win, and start looking at other strange effects to explain. Because once you allow yourself to ignore basic physics in your theory, all sorts of phenomena can be explained.

McCulloch’s model vs MoND and Newton for some dwarf galaxies. Credit: M.E. McCulloch.

In his most recent work, McCullogh claims MiHsC can explain the odd behavior of rotating galaxies. It’s long been known that galaxies rotate faster than expected. Given the amount of mass we can directly see in a galaxy, most of them should simply fly apart. The most popular solution to this conundrum is that galaxies contain dark matter, but other ideas such as Modified Newtonian Dynamics (MoND) have been proposed. Like MoND, MiHsC proposes that the inertia of an object is less at small accelerations, so the weak gravity of a galaxy can keep stars from flying away. Starting with an equation for modified inertial mass, the paper derives the predicted rotation speeds for several dwarf galaxies. It then compares observed rotation speeds with the predictions of Newtonian gravity (without dark matter), MoND, and MiHsC. Newtonian gravity fails (as has long been known), and the other two models agree with the data equally well, though with uncertainties on the order of 30% calling the data a good fit is a bit generous. McCullogh then argues that MiHsC is inherently better than MoND, since MoND relies upon an adjustable parameter. Nevermind the fact that MiHsC violates established physics, while MoND is simply descriptive.

By itself this is pretty standard for a speculative paper: here’s a wild idea, it can kinda explain a strange physical effect, maybe it’s worth exploring further. It’s a kind of “what if” paper that could lead to interesting models, but doesn’t really prove anything. Sure, MiHsC roughly agrees with the galaxy rotation curves, but so do a dozen other speculative models.  But McCullogh claims on his blog that the model not only predicts galactic rotation curves without dark matter, it predicts cosmic expansion without dark energy, solves the Pioneer anomaly and the flyby anomaly, could be used to create free energy through sonoluminescence, etc. It’s everything we could ever wish for. These claims reiterated in the popular press without any critical analysis. As a result, the model has built up a fan following who think that skeptical scientists are just haters trying to bury the next Einstein.

But that’s not how science is done. To be a viable model MiHsC will have to address its contradictions with established theories, and that will prove extremely difficult. Claiming victory is easier, but it’s an approach that will only get you lost in the woods.

Paper: M.E. McCulloch. Low-acceleration dwarf galaxies as tests of quantised inertia. Astrophysics and Space Science (2017)

Paper: M.E. McCulloch. Testing quantised inertia on the emdrive. arXiv:1604.03449 [physics.gen-ph] (2016)

Paper: M. E. McCulloch. Modelling the Pioneer anomaly as modified inertia. MNRAS,376,338-342 (2007)

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There has been a lot of digital ink spilled over the recent paper on the reactionless thrust device known as the EMDrive. While it’s clear that a working EM Drive would violate well established scientific theories, what isn’t clear is how such a violation might be resolved. Some have argued that the thrust could be an effect of Unruh radiation, but the authors of the new paper argue instead for a variation on quantum theory known as the pilot wave model. 

One of the central features of quantum theory is its counter-intuitive behavior often called particle-wave duality. Depending on the situation, quantum objects can have characteristics of a wave or characteristics of a particle. This is due to the inherent limitations on what we can know about quanta. In the usual Copenhagen interpretation of quantum theory, an object is defined by its wavefunction. The wavefunction describes the probability of finding a particle in a particular location. The object is in an indefinite, probabilistic state described by the wavefunction until it is observed. When it is observed, the wavefunction collapses, and the object becomes a definite particle with a definite location.

While the Copenhagen interpretation is not the best way to visualize quantum objects it captures the basic idea that quanta are local, but can be in an indefinite state. This differs from the classical objects (such as Newtonian theory) where things are both local and definite. We can know, for example, where a baseball is and what it is doing at any given time.

The pilot wave model handles quantum indeterminacy a different way. Rather than a single wavefunction, quanta consist of a particle that is guided by a corresponding wave (the pilot wave). Since the position of the particle is determined by the pilot wave, it can exhibit the wavelike behavior we see experimentally. In pilot wave theory, objects are definite, but nonlocal. Since the pilot wave model gives the same predictions as the Copenhagen approach, you might think it’s just a matter of personal preference. Either maintain locality at the cost of definiteness, or keep things definite by allowing nonlocality. But there’s a catch.

Although the two approaches seem the same, they have very different assumptions about the nature of reality. Traditional quantum mechanics argues that the limits of quantum theory are physical limits. That is, quantum theory tells us everything that can be known about a quantum system. Pilot wave theory argues that quantum theory doesn’t tell us everything. Thus, there are “hidden variables” within the system that quantum experiments can’t reveal. In the early days of quantum theory this was a matter of some debate, however both theoretical arguments and experiments such as the EPR experiment seemed to show that hidden variables couldn’t exist. So, except for a few proponents like David Bohm, the pilot wave model faded from popularity. But in recent years it’s been demonstrated that the arguments against hidden variables aren’t as strong as we once thought. This, combined with research showing that small droplets of silicone oil can exhibit pilot wave behavior, has brought pilot waves back into play.

How does this connect to the latest EM Drive research? In a desperate attempt to demonstrate that the EM Drive doesn’t violate physics after all, the authors spend a considerable amount of time arguing that the effect could be explained by pilot waves. Basically they argue that not only is pilot wave theory valid for quantum theory, but that pilot waves are the result of background quantum fluctuations known as zero point energy. Through pilot waves the drive can tap into the vacuum energy of the Universe, thus saving physics! To my mind it’s a rather convoluted at weak argument. The pilot wave model of quantum theory is interesting and worth exploring, but using it as a way to get around basic physics is weak tea. Trying to cobble a theoretical way in which it could work has no value without the experimental data to back it up.

At the very core of the EM Drive debate is whether it works or not, so the researchers would be best served by demonstrating clearly that the effect is real. While they have made some interesting first steps, they still have a long way to go.

Paper: Harris, D.M., et al. Visualization of hydrodynamic pilot-wave phenomena, J. Vis. (2016) DOI 10.1007/s12650-016-0383-5

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The reactionless thruster known as the EM Drive has stirred heated debate over the past few years. If successful it could provide a new and powerful method to take our spacecraft to the stars, but it has faced harsh criticism because the drive seems to violate the most fundamental laws of physics. One of the biggest criticisms has been that the work wasn’t submitted for peer review, and until that happens it shouldn’t be taken seriously. Well, this week that milestone was reached with a peer-reviewed paper. The EM Drive has officially passed peer review. 

It’s important to note that passing peer review means that experts have found the methodology of the experiments reasonable. It doesn’t guarantee that the results are valid, as we’ve seen with other peer-reviewed research such as BICEP2. But this milestone shouldn’t be downplayed either. With this new paper we now have a clear overview of the experimental setup and its results. This is a big step toward determining whether the effect is real or an odd set of secondary effects. That said, what does the research actually say?

The basic idea of the EMDrive is an asymmetrical cavity where microwaves are bounced around inside. Since the microwaves are trapped inside the cavity, there is no propellent or emitted electromagnetic radiation to push the device in a particular direction, standard physics says there should be no thrust on the device. And yet, for reasons even the researchers can’t explain, the EM Drive does appear to experience thrust when activated. The main criticism has focused on the fact that this device heats up when operated, and this could warm the surrounding air, producing a small thrust. In this new work the device was tested in a near vacuum, eliminating a major criticism.

The relation of thrust to power for the EM Drive. Credit: Smith, et al.

What the researchers found was that the device appears to produce a thrust of 1.2 ± 0.1 millinewtons per kilowatt of power in a vacuum, which is similar to the thrust seen in air. By comparison, ion drives can provide a much larger 60 millinewtons per kilowatt. But ion drives require fuel, which adds mass and limits range. A functioning EM drive would only require electric power, which could be generated by solar panels. An optimized engine would also likely be even more efficient, which could bring it into the thrust range of an ion drive.

While all of this is interesting and exciting, there are still reasons to be skeptical. As the authors point out, even this latest vacuum test doesn’t eliminate all the sources of error. Things such as thermal expansion of the device could account for the results, for example. Now that the paper is officially out, other possible error sources are likely to be raised. There’s also the fact that there’s no clear indication of how such a drive can work. While the lack of theoretical explanation isn’t a deal breaker (if it works, it works), it remains a big puzzle to be solved.  The fact remains that experiments that seem to violate fundamental physics are almost always wrong in the end.

I’ve been pretty critical of this experiment from the get go, and I remain highly skeptical. However, even as a skeptic I have to admit the work is valid research. This is how science is done if you want to get it right. Do experiments, submit them to peer review, get feedback, and reevaluate. For their next trick the researchers would like to try the experiment in space. I admit that’s an experiment I’d like to see.

Paper: Harold White, et al. Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum. Journal of Propulsion and Power. DOI: 10.2514/1.B36120 (2016)

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