EmDrive

EmDrive

EmDrive experiment, Eagleworks laboratory, 2013
Country of origin	United States
Date	2001
Status	Device concept
Performance
Thrust, sea-level	0 N (0 ozf)[1]

The EmDrive is a controversial device first proposed in 2001,^[2][3][4][5] purported by its inventors to be a reactionless drive. While no mechanism for operation was proposed, this would violate the law of conservation of momentum and other laws of physics.^{[6][7][8][9][10]} The concept has at times been referred to as a resonant cavity thruster.^[11][12] The idea is generally considered by physicists to be pseudoscience.

Neither person who claims to have invented it committed to details about it beyond showing prototypes they have built.^[13] While the lack of a published design or mechanism makes it hard to say whether a given object is an example of an EmDrive, over the years prototypes based on its public descriptions have been constructed and tested.

In 2016, Harold White's group at NASA observed a small apparent thrust from one such test,^[14] however subsequent studies suggested this was a measurement error caused by thermal gradients.^[15][16] 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.^[1]

No other published experiment measured apparent thrust greater than the experiment's margin of error.^[17] 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."^[1]