Dr. Christopher Bird

Once more the internet is buzzing with reports over the past few weeks and months that NASA has successfully tested a 'warp drive' prototype, leading to many fanciful speculations about travelling to distant stars in the near future. I have said from the start that I do not believe these reports - for several reasons based in accepted science - and indeed today NASA has officially denied it.

First, what NASA actually tested is a device called an EMDrive, in which microwave radiation is contained in a specially designed chamber. The claim is that this device exhibits thrust without using any fuel. If that were true, it would be a great leap forward for space exploration, since fuel transportation is one of the greatest limitations at present. That is why there is so much serious research into solar sails or similar devices, in which the fuel is stored either on Earth or the Sun itself is used as an energy source.

However there are a number of problems with the current claims regarding the EMDrive.

The first is simply that it is not a warp drive. To be a warp drive it would have to warp spacetime, and this does not seem to. (Of interest is that the original experiments on the EMDrive were done by the same team that previously claimed q-drives were warping space). Maybe that will be proven to be untrue later, through some strange modification of general relativity or a new solution of Einstein's equations. But for now, it is not a warp drive.

There are also claims that the device was tested in a vacuum and shown to produce thrust. Except the actual test results show that most of the trials it did not develop any thrust, and the few times it did the amount of thrust was on the order of thirty to fifty micronewtons. The gravitational force on a rain drop is approximately a thousand times greater. And the uncertainty in the measurements is approximately thirty micronewtons or more. 

So what is actually being seen in these few positive tests? It is too early to know for sure. Some speculations though include experimental error and the force does not exist at all, or that the device is interaction with Earth's magnetic field, or that some minor event nearby (ie a person walks past the lab) generated enough gravity to affect the measurement. But whatever is causing this apparent thrust, it is not consistent in the tests and therefore is hard to attribute to the EMDrive itself.

Which makes sense, because the most basic laws of physics do not allow the EMDrive to work. First, it would appear to gain energy - although this could be converting electrical energy into kinetic energy, but that still means it is using fuel in the form of a battery. Second, it definitely violates conservation of momentum, which according to Noether's law can only happen if the laws of physics themselves are not constant through space. The violate momentum conservation in a NASA lab would mean that the laws of physics are different at each point in the lab, and I don't think anyone is willing to make that claim. 

And so while there is a very tiny chance that the EMDrive is a signal of some new physics that has never been observed or theorized before, it is far more likely that just like faster-than-light neutrinos, it is an experimental error that has found a life on the internet far greater than it really deserves.