The EmDrive: Fact or Fiction?

The EmDrive is a concept for a thruster for spacecraft, first written about in 2001.

The EmDrive is purported to generate thrust by reflecting microwaves inside the device, in a way that would violate the law of conservation of momentum.

There is no official design for this device, and neither person who claims to have invented it has committed to an explanation for how it could operate as a thruster or what elements define it.

Since 2008, a few physicists have tested their own models, trying to reproduce the results claimed by Shawyer and Fetta.

In 2016, Harold White's group at NASA's Advanced Propulsion Physics Laboratory reported in the Journal of Propulsion and Power that a test of their own model had observed a small thrust.

In 2021, Martin Tajmar's group at the Dresden University of Technology replicated White's test, observing apparent thrusts similar to those measured by the NASA team, and then made them disappear again when measured using point suspension.

No other published experiment has measured apparent thrust greater than the experiment's margin of error.

Tajmar's group published three papers in 2021 claiming that all published results showing thrust had been false positives, explaining each by outside forces.

Media coverage of experiments using these designs has been polarized.

In 2006, the New Scientist magazine published an article about the EmDrive, which portrayed it as plausible.

Mathematical physicist John C. Baez and Australian science-fiction writer Greg Egan criticized the article, saying that the positive results reported by Shawyer were likely misinterpretations of experimental errors.

In 2014, White's first conference paper suggested that resonant cavity thrusters could work by transferring momentum to the "quantum vacuum virtual plasma", a new term he coined.

Baez and Carroll criticized this explanation, because in the standard description of vacuum fluctuations, virtual particles do not behave as a plasma; Carroll also noted that the quantum vacuum has no "rest frame", providing nothing to push against, so it can't be used for propulsion.

In 2015, physicists Eric W. Davis at the Institute for Advanced Studies in Austin and Sean M. Carroll at the California Institute of Technology concluded that the thrust measurements reported in papers by both Tajmar and White were indicative of thermal effect errors.

In May 2018, researchers from the Institute of Aerospace Engineering at Technische Universität Dresden, Germany, concluded that the dominant effect underlying the apparent thrust could be clearly identified as an artifact caused by Earth's magnetic field interacting with power cables in the chamber, a result that other experts agree with.

In March 2021, Tajmar's group published a definitive analysis of their own past experiments and those of others, showing that all could be explained by and reproduced via outside forces, refuting all EmDrive claims.

The EmDrive has never been successfully demonstrated or replicated.

In 2003, an EmDrive inventor, Roger Shawyer, announced that he had developed a propulsion system that used microwaves to generate thrust.

The thrust produced is said to be small, but some proponents of the technology believe that it could be used to propel spacecraft.

In 2014, Shawyer presented ideas for 'second-generation' EmDrive designs and applications at the annual International Astronautical Congress.

In 2016, Shawyer filed further patents and launched a new company, Universal Propulsion Ltd., as a joint venture with Gilo Industries Group, a small UK aerospace company.

In 2017, a Chinese researcher working under Yang at NWPU built a resonant cavity thruster.

In 2016, Yue Chen filed several patent applications in China describing various RF resonant cavity thruster designs.

In September 2017, CAST announced plans to conduct tests on a resonant cavity thruster in orbit.

The conservation of momentum is a symmetry of nature and all proposed theories for how the EmDrive works violate it.

Harold White's theory of the EmDrive relies on asymmetric or dynamical Casimir effects.

Tests by inventors have failed to produce any measurable thrust.

Juan Yang's theory of the EmDrive was based on a valid electro-magnetic theory.

The team at NASA Eagleworks investigated ideas for a wide range of untested and fringe proposals, including Alcubierre drive.

Yang's results were not reproducible, and suggest that external power sources were responsible for the observed thrust in their 2010 experiment.

White's team has since been focused on studying exotic propulsion concepts, and has not published any further results on the EmDrive.