I have to be honest, I don’t believe it. Whenever research seems to show a phenomenon that defies the known laws of physics, that is my initial reaction. It’s a good default approach, and so far it has proven correct. I didn’t believe it when researchers claimed they found neutrinos traveling faster than light. It turns out, it was a flaw in the equipment. In fact, I have not believed the many claims over the years of faster than light phenomena, all of which have fallen away. I did not believe the countless claims of free energy or perpetual motion, all of which have failed. I did not believe claims of cold fusion, and still don’t. I did not believe it when engineers claimed to have produced propellantless acceleration (the EM drive). That one crashed and burned as well.

These claims typically have two features in common. They are based on an observed anomaly, and that anomaly is very tiny. It’s just more likely that a tiny anomaly that appears to break the laws of physics is the result of a tiny error, not that the laws of physics as we currently know them are wrong. This is especially true when talking about conservation laws, which are so well established that we can treat them as – laws.

I always acknowledge that our understanding of the laws of physics is incomplete, and there could be some phenomenon hiding in the parts we have not figured out yet (quantum gravity is a good example) that could allow for these apparent anomalies. I’m just not holding my breath. Also, the bar we set for the threshold of evidence before accepting the anomaly as real should be incredibly high. Again, history has proven countless times that this is a good approach.

Therefore my reaction to the study, by mainstream scientists, that they have figured out a way to produce locomotion by shape change alone, without interaction with the environment. This would indeed be huge, even if the effect is super tiny. Conservation of momentum means that you cannot simply produce net momentum out of nothing. You have to “steal” it from your environment. In practical terms this means that you push on something or you use propellant. When you walk friction allows you to push against the surface of the Earth, taking an infinitessimal amount of its momentum. When a rocket accelerates through space it has to throw stuff out its back end, so the net momentum of the system is unchanged.

But I have to admit, the paper is technically dense and a little difficult to understand. Also, the researchers are not being crystal clear exactly what they have accomplished. This is what they say in their abstract:

It produces shape changes comparable to the environment’s inverse curvatures and generates movement of 10^−1 cm per gait. While this simple geometric effect predominates over short time, eventually the dissipative (frictional) and conservative forces, ubiquitous in real systems, couple to it to generate an emergent dynamics in which the swimming motion produces a force that is counter-balanced against residual gravitational forces. In this way, the robot both swims forward without momentum and becomes fixed in place with a finite momentum that can be released by ceasing the swimming motion.

Trying to parse this, it seems like the robot was able to move, but without momentum. Also, while they minimized the effects of friction and gravity in the system, they are still there, and eventually neutralize any movement. It seems like what they are saying is that you can get part of the apparatus to “move” but without actual acceleration, and then when it stops it is in a new fixed position, so it has slightly changed its position without ever acquiring any momentum, and that this phenomenon can only happen along a curved surface. If this worked, you can then just repeat the process over and over, inching along the curved surface without violating the conservation of momentum.

What makes the claim somewhat plausible is that the system never acquires any net momentum.  But then, how does it move? Internal movement (like a cat flipping around when dropped upside down) is possible, but not moving with respect to the environment unless you are interacting with that environment in some way. Here is what I suspect – the anomaly here is that gravity or the small amount of residual friction is somehow at work. Small hidden phenomena always seem to be the answer to similar apparent anomalies.

For example, more than once physicists thought they observed something moving faster than light, but it turns out that this was an illusion. Part of the phenomenon appeared to move faster than light because it moved from the back to the front of the movement, but the entire phenomenon was not moving faster than light. Free energy devices often are harvesting energy from some subtle and missed phenomena.

In any case, I wish the researchers here were explicit as to what was NOT happening in their experiment. Instead, one of the authors gave this quote:

“This research also relates to the ‘Impossible Engine’ study,” said Rocklin. “Its creator claimed that it could move forward without any propellant. That engine was indeed impossible, but because spacetime is very slightly curved, a device could actually move forward without any external forces or emitting a propellant – a novel discovery.”

This is inviting misinterpretation, and is frankly irresponsible – unless they are actually claiming propellantless drive, which is much worse. Notice how he says “move forward” and not “accelerate”. I think that’s the key. Somehow this is like the flipping cat, and they are just misinterpreting the overall motion as moving forward (or perhaps they are not, and are just not communicating well).

For me the ultimate test of any such claims is to build a workable device based on the alleged principles discovered. If you think you have discovered a source of free energy, then build a device that can power something substantial without external inputs. It’s never been done. If you think you have a propellantless drive, then build a ship that can accelerate through space using those principles.  If the phenomenon does not scale up to something useful at the macro scale, then it is very likely the anomaly is just a tiny error in your setup. A real phenomenon should scale up. Tiny errors probably don’t, they remain tiny.

In this case the authors are not explicitly claiming a propellantless drive, but they should have made it crystal clear that they weren’t.

As an aside, it would be fantastic if some quirk of physics does allow for propellantless acceleration. If there were some way to convert energy into momentum, without interaction with the environment, that would profoundly change space travel.  This is one case where I really wish I were wrong. But those pesky laws of physics will not be denied.