The somewhat fantastical EMDrive (short for Electromagnetic Drive) recently returned to the public eye after an academic claimed to have recorded the drive producing measurable thrust. The experiments from Professor Martin Tajmar's group at the Dresden University of Technology have spawned numerous overexcited headlines making claims that -- let's be very clear here -- are not supported by the science.
...Eagleworks, a NASA-based group, built a prototype and last year reported 30-50 micronewtons of thrust that could not be explained by any conventional theory. This work was not peer-reviewed. Now, Tajmar's group in Dresden say they have built a new version of the EMDrive and detected 20 micronewtons of thrust. This is a much smaller value, but still significant if it really is generated by some new principle.
Straightaway, there are problems with this experiment. The abstract states: "Our test campaign cannot confirm or refute the claims of the EMDrive." Then, a careful reading of the paper reveals this observation: "The control experiment actually gave the biggest thrust . We were really puzzled by this large thrust from our control experiment where we expected to measure zero."
Yes, the control experiment designed not to generate any thrust still measures a thrust. Then there's the peculiar gradual way the thrust seems to turn on and off that looks suspiciously like a thermal effect, and then there are acknowledged heating problems. All this leads to the conclusion stated in the paper that "such a set-up does not seem to be able to adequately measure precise thrusts." Similar problems were seen by the Eagleworks group, with thrust also mysteriously appearing in their control test.
Taken together, these results strongly suggest that the measured signatures of thrust are subtle experimental errors. Possible sources include thermal effects, problems with magnetic shielding or even a non-uniform gravitational field in the laboratory leading to erroneous force measurements.As a comparison, the force measured in this latest experiment is roughly comparable to the gravitational attraction between two average-sized people (100kg) standing about 15cm apart.
...The experimental scientists involved have done their jobs to the best of their ability, having tested a hypothesis - albeit a spectacularly unlikely one - and reported their results. These scientists aren't actually claiming to have invented a warp drive or to have broken the laws of physics. All they're saying at the moment is that they've found something odd and unexplained that might be something new but is likely an experimental artefact that needs further study. The panoply of clickbait headlines and poorly researched articles on the topic are doing something of a disservice to their scientific integrity by claiming otherwise.
