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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| EmDrive | 3/5 | https://en.wikipedia.org/wiki/EmDrive | reference | science, encyclopedia | 2026-05-05T09:19:20.530876+00:00 | kb-cron |
== Theoretical inconsistencies == All proposed theories for how the EmDrive works violate the conservation of momentum, which states any interaction cannot have a net force (i.e., the net sum of all forces is zero); a consequence of the conservation of momentum is Newton's third law, where for every action there is an equal and opposite reaction. Also, because force × velocity = power, any such device would violate conservation of energy when moving at a high enough velocity. The conservation of momentum is a symmetry of nature. An often-cited example of apparent nonconservation of momentum is the Casimir effect, in the standard case where two parallel plates are attracted to each other. However the plates move in opposite directions, so no net momentum is extracted from the vacuum and, moreover, energy must be put into the system to take the plates apart again. Assuming homogeneous electric and magnetic fields, it is impossible for the EmDrive, or any other device, to extract a net momentum transfer from either a classical or quantum vacuum. Extraction of a net momentum "from nothing" has been postulated in an inhomogeneous vacuum, but this remains highly controversial as it will violate Lorentz invariance. Both Harold White's and Mike McCulloch's theories of how the EmDrive could work rely on these asymmetric or dynamical Casimir effects. However, if these vacuum forces are present, they are expected to be exceptionally tiny based on our current understanding, too small to explain the level of observed thrust. In the event that observed thrust is not due to experimental error, a positive result could indicate new physics.
== Tests and experiments ==
=== Tests by inventors === In 2004, Shawyer claimed to have received seven independent positive reviews from experts at BAE Systems, EADS Astrium, Siemens and the IEE. The technical director of EADS Astrium (Shawyer's former employer) denied this in the strongest terms, stating:
I reviewed Roger's work and concluded that both theory and experiment were fatally flawed. Roger was advised that the company had no interest in the device, did not wish to seek patent coverage and in fact did not wish to be associated with it in any way. In 2011, Fetta claimed to have tested a superconducting version of the Cannae drive, suspended inside a liquid-helium-filled dewar, with inconclusive results. None of these results were published in the scientific literature, replicated by independent researchers, or replicated consistently by the inventors. In a few cases details were posted for a time on the inventors' websites, but no such documents remained online as of 2019. In 2015, Shawyer published an article in Acta Astronautica, summarising seven existing tests on the EmDrive. Of these, four produced a measured force in the intended direction, three produced thrust in the opposite direction, and in one test thrust could be produced in either direction by varying the spring constants in the measuring apparatus.
=== Northwestern Polytechnical University === In 2008, a team of Chinese researchers led by Juan Yang (杨涓), professor of propulsion theory and engineering of aeronautics and astronautics at Northwestern Polytechnical University (NWPU) in Xi'an, China, said that they had developed a valid electro-magnetic theory behind a microwave resonant cavity thruster. A demonstration version of the drive was built and tested with different cavity shapes and at higher power levels in 2010. Using an aerospace engine test stand usually used to precisely test spacecraft engines like ion drives, they reported a maximum thrust of 720 mN at 2,500 W of input power. Yang noted that her results were tentative, and said she "[was] not able to discuss her work until more results are published". In a 2014 follow-up experiment (published in 2016), Yang could not reproduce the 2010 observation and suggested it was due to experimental error. They had refined their experimental setup, using a three-wire torsion pendulum to measure thrust, and tested two different power setups. They concluded that they were unable to measure significant thrust; that "thrust" measured when using external power sources (as in their 2010 experiment) could be noise; and that it was important to use self-contained power systems for these experiments, and more sensitive pendulums with lower torsional stiffness.
=== NASA Eagleworks === Since 2011, White had a team at NASA known as the Advanced Propulsion Physics Laboratory, or Eagleworks Laboratories, devoted to studying exotic propulsion concepts. The group investigated ideas for a wide range of untested and fringe proposals, including Alcubierre drives, drives that interact with the quantum vacuum, and RF resonant cavity thrusters. In 2014, the group began testing resonant cavity thrusters and in July, White reported tentative positive results for evaluating a tapered RF resonant cavity. Their first tests of this tapered cavity were conducted at very low power (2% of Shawyer's 2002 experiment). A net mean thrust over five runs was measured at 91.2 μN at 17 W of input power. The experiment was criticized for its low power, small data set, and for not having been conducted in vacuum, to eliminate thermal air currents. The group announced a plan to upgrade their equipment to higher power levels, and to use a test framework subject to independent verification and validation at one or more major research centers. This did not happen. They later conducted experiments in vacuum at 40-80W of input power, publishing the results in November 2016 in the Journal of Propulsion and Power, under the title "Measurement of Impulsive Thrust from a Closed Radio-Frequency Cavity in Vacuum". The study said their system was "consistently performing with a thrust-to-power ratio of 1.2±0.1mN/kW", but also enumerated many potential sources of error. This was the first such paper published in a peer-reviewed journal, however the experiment was again criticized for its small dataset and missing details about the experimental setup, which was again not independently validated.