EmDrive
Controversial reactionless drive concept refuted by experiments.
The EmDrive, a device first described in 2001, is a controversial concept that its creators claim operates as a reactionless drive. Because no working mechanism has ever been proposed, the device’s alleged behavior would violate the conservation of momentum and other established physics. Physicists and engineers widely classify the EmDrive as pseudoscience.
The idea was introduced by Roger Shawyer in 2001, who called his conical design an EmDrive and said it produced thrust toward the cone’s base. Guido Fetta later built a similar device, the Cannae Drive, using a pillbox-shaped cavity. Neither inventor has provided detailed designs or mechanisms beyond showing prototypes.
Since 2008, several researchers have built and tested their own versions. Juan Yang’s team at Northwestern Polytechnical University in Xi’an could not reproducibly measure thrust over four years. In 2016, Harold White’s group at NASA reported a small apparent thrust in the Journal of Propulsion and Power, but later studies attributed this to thermal gradient errors. Martin Tajmar’s group at the Dresden University of Technology began testing in 2015 and, by 2021, concluded that all observed thrusts were false positives. Their 2021 papers showed that the apparent thrusts could be reproduced by outside forces—such as Earth’s magnetic field interacting with power cables—and that when measured using point suspension, the signals disappeared. They stated their measurements refute all EmDrive claims by at least three orders of magnitude.
Media coverage has been polarized. In 2006, New Scientist described the EmDrive as an “impossible” drive, drawing both credulous and dismissive attention. After White’s 2014 test reports, some outlets were criticized for claiming NASA had validated the device. Scientists have noted the lack of unbiased coverage. In 2006, mathematical physicist John C. Baez and science-fiction writer Greg Egan said Shawyer’s positive results likely stemmed from experimental errors. In 2014, White suggested the thrust could come from transferring momentum to a “quantum vacuum virtual plasma,” a term he coined. Baez and physicist Sean M. Carroll criticized this, noting that virtual particles do not behave as a plasma and that the quantum vacuum has no rest frame to push against. Physicists James F. Woodward and Heidi Fearn also published papers showing that electron-positron virt
- first_proposed
- 2001
- field
- Propulsion physics
- known_for
- Reactionless drive claims
- status
- Refuted by multiple experiments
- key_inventors
- Roger Shawyer, Guido Fetta
Lore & Background
The first design of a resonant cavity thruster claiming to be a reactionless drive was by Roger Shawyer in 2001. He called his conical design an 'EmDrive', and claimed that it produced thrust in the direction of the base of the cone. Guido Fetta later built a 'Cannae Drive', based in part on Shawyer's concept, using a pillbox-shaped cavity. Neither person who claims to have invented the EmDrive committed to details about the device beyond showing prototypes they have built.
Reader's Guide
The EmDrive drew attention, both credulous and dismissive, when New Scientist wrote about it as an 'impossible' drive in 2006. Media outlets were later criticized for misleading claims that a resonant cavity thruster had been 'validated by NASA' following Harold White's first tentative test reports in 2014. In 2016, White's group at NASA observed a small apparent thrust from one test, however subsequent studies suggested this thrust was a measurement error caused by thermal gradients. In 2018 and 2021, Martin Tajmar's group at the Dresden University of Technology replicated and refuted White's results, observing apparent thrusts similar to those measured by his team, and then made them disappear again when measured using point suspension. Tajmar's group published three papers in 2021 claiming that all published results showing thrust had been false positives, explaining each by outside forces. They concluded, 'Our measurements refute all EmDrive claims by at least 3 orders of magnitude.' No other published experiment resulted in apparent thrust greater than the experiment's margin of error.
Did You Know?
- The EmDrive was first proposed by Roger Shawyer in 2001.
- In 2016, Harold White's NASA group observed a small apparent thrust later attributed to thermal gradients.
- Martin Tajmar's group at Dresden University of Technology refuted all EmDrive claims by at least 3 orders of magnitude in 2021.
- Physicists John C. Baez and Sean M. Carroll criticized the quantum vacuum explanation for the EmDrive.
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