New Scientist.^[1] ran a cover story for their September 8, 2006 issue reporting that a person named Roger Shawyer had developed a spacecraft propulsion system he was calling an EmDrive or a Relativity Drive. The device is a Magnetron with a specially shaped fully enclosed tapering resonator cavity whose area is greater at one end. The inventor claims that the device generates thrust even though no detectable energy leaves the device. The inventor proposes to use it as a spacecraft propulsion system that uses no fuel. Image File history File links Unbalanced_scales. ... Image File history File links Unbalanced_scales. ... Shortcut: WP:NPOV Wikipedia policy is that all articles should be written from a neutral point of view. ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. ... A cavity magnetron is a high-powered vacuum tube that generates coherent microwaves. ... It has been suggested that this article or section be merged into resonator. ... A remote camera captures a close-up view of a Space Shuttle Main Engine during a test firing at the John C. Stennis Space Center in Hancock County, Mississippi Spacecraft propulsion is used to change the velocity of spacecraft and artificial satellites, or in short, to provide delta-v. ...

The device's operation as described seemingly violates several basic laws of physics, notably conservation of momentum, though the inventor insists to the contrary. On his homepage[1] the inventor claims that independent peer-review is underway, but so far no publication is availible. Physics (Greek: (phúsis), nature and (phusiké), knowledge of nature) is the science concerned with the fundamental laws of the universe. ... Peer review (known as refereeing in some academic fields) is a process of subjecting an authors scholarly work or ideas to the scrutiny of others who are experts in the field. ...

Principle of operation

The device exploits an idea first suggested by Allen Cullen in the 1950's, an electrical engineer then at University College London, that involves forces created by reflecting microwaves between opposite walls of a cavity. The "idea" is to try to design a cavity in such a manner that forces on one side are greater than the other. 1950 (MCML) was a common year starting on Sunday (link will take you to calendar). ... For the Technical Symposium of NITK Surathkal Engineer , see Engineer (Technical Fest). ... The term university college is used in a number of countries to denote institutions that provide tertiary education but do not have full or independent university status. ... This article is about the capital of England and the United Kingdom. ... In physics, force is an influence that may cause a body to accelerate. ...

The drive comprises a resonant cavity flooded with microwave radiation. The radiation exerts radiation pressure on the walls of the cavity, and normal Newtonian mechanics would indicate that, no matter what shape the cavity is, the forces exerted upon it from within must balance to zero. Shawyer claims that relativistic effects cause a cavity shaped like a truncated cone to experience a larger force against the large end than the small end, due to the group velocity of the wave changing as the local diameter of the cavity varies. A cavity resonator uses resonance to amplify a wave. ... Microwaves are electromagnetic waves with wavelengths longer than those of terahertz (THz) frequencies, but relatively short for radio waves. ... Radiation pressure is the pressure exerted upon any surface exposed to electromagnetic radiation. ... It has been suggested that this article or section be merged with Classical mechanics. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... The group velocity of a wave is the velocity with which the variations in the shape of the waves amplitude (known as the modulation or envelope of the wave) propagate through space. ...

The increased confinement of the tapered end of the cone leads to a higher effective propagation constant (phase velocity). It also leads to local reflections which account for the apparent force imbalance when considering only the end walls. However, since it is the phase of the light rather than the actual photons bouncing off the walls, each force acts quasi independently from another - much like in a ring laser gyroscope where the beams act as if having an external frame of reference (which they have, since the speed of light is constant). The same principle applies to the EmDrive. A ring laser gyroscope uses interference of laser light within a bulk optic ring to detect changes in orientation and spin. ... A line showing the speed of light on a scale model of Earth and the Moon The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness. It is the speed of all electromagnetic radiation...

No microwaves or anything else are allowed to leave the device. Since nothing leaves the drive for propulsive purposes an EmDrive can be classed as a reactionless drive. Thus the principle by which the EmDrive is supposed to operate seems to violate conservation of momentum. It is known that the physics equations describing microwaves, Maxwell's equations, conserve momentum, and this would seem to cast doubt on Shawyer's derivation of a thrust effect. In his paper (attached), Shawyer thus takes the following view: any thrust extracted from his device is directly withdrawn from the energy stored in his cavity (due to the Q reflections an average wave encounters when inserted into the cavity, the energy levels quickly build up). In other words: the apparent force on the wider diameter of the cone seems to wane. The extent to which that happens perfectly matches the amount predicted by the law of conservation of momentum. A reactionless drive or reactionless thruster (sometimes even reactionless engine) is a hypothetical form of thrust that does not require any outside force to move. ... In classical mechanics, momentum (pl. ... In electromagnetism, Maxwells equations are a set of equations developed in the latter half of the nineteenth century by James Clerk Maxwell. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ...

Criticism

The EmDrive was the cover story for the September 8, 2006 issue of New Scientist.^[1] After receiving criticism that no peer-reviewed publications on the subject had been made, Mr. Shawyer submitted a theory paper to New Scientist (which is not a peer reviewed scientific journal) ^[2] Shawyer's paper was almost immediately challenged^[3] by Dr. John Costella, a theoretical physicist and electrical engineer who works for the Australian Department of Defence, whose Ph.D. is in relativistic electrodynamics, the field of physics that Mr. Shawyer relies on to support his theory. New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... Peer review (known as refereeing in some academic fields) is a scholarly process used in the publication of manuscripts and in the awarding of funding for research. ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... This article or section does not cite its references or sources. ...

Prototype tests

Shawyer claims^[1] to have constructed a prototype weighing 9 kilogrammes that consumes 700 watts of power and produces 88 millinewtons of force.

The limiting factor for performance is claimed to be the Q factor of the cavity, as microwave energy lost to heating the cavity reduces the field strength within, so Shawyer is experimenting with a cavity lined in a superconducting material that may produce Q factors sufficient to build a device capable of generating 30 newtons per watt. The Q factor or quality factor is a measure of the rate at which a vibrating system dissipates its energy into heat. ...

These results have neither been reproduced by other scientists or engineers, nor have they been published in a peer-reviewed scientific journal. Peer review (known as refereeing in some academic fields) is a scholarly process used in the publication of manuscripts and in the awarding of funding for research. ... This article or section does not cite its references or sources. ...

New Scientist article

EmDrive was featured on the cover of issue 2568 of New Scientist, a weekly science magazine. The article portrayed the device as plausible, and emphasized the arguments of those who held that point of view, although it did quote one engineer as saying "it's a load of bloody rubbish." The article included the following arguments from proponents of the theory: New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ...

• With a grant from the UK government's Department of Trade and Industry of £250,000, (actually two grants; one a feasibility study of £45,000 and a second of £81,000 to build a demonstration engine - source SPR Ltd.) a commercial regulatory and support agency,^[4] Shawyer has built two prototypes that reportedly produce 16mN and 300mN of thrust respectively; each using 1kW of electrical power. A condition of the funding was independent analysis, which was recently completed by John Spiller who says "The thruster's design is practical and could be adapted fairly easily to work in outer space". Shawyer claims that he has been visited by representatives from China and the US Air Force, but ESA has not yet shown much interest. He estimates that his design could save the aerospace community $15 billion over the next ten years.

• Engineers in Germany have created superconducting resonators (for use in particle accelerators) with Q values of several billion, which Shawyer claims would equate to a thrust of 30kN per kilowatt, "enough to lift a large car". Shawyer states that the thruster works best while stationary relative to their thrust.

New Scientist has drawn great criticism from the scientific community due to the uncritical treatment of EmDrive in its article. Science fiction writer Greg Egan distributed a public letter stating that "a sensationalist bent and a lack of basic knowledge by its writers" was making the magazine's coverage sufficiently unreliable "to constitute a real threat to the public understanding of science". In particular, Egan found himself "gobsmacked by the level of scientific illiteracy" in the magazine's coverage of the EmDrive, where New Scientist allowed the publication of "meaningless double-talk" designed to bypass a fatal objection to Sawyer's proposed space drive, namely that it violates the conservation of momentum. Egan urged those reading his letter to write to New Scientist and pressure the magazine to raise its standards, instead of "squandering the opportunity that the magazine's circulation and prestige provides" for genuine science education. The letter was endorsed by mathematical physicist John C. Baez and posted on his blog.^[5] Egan has also recommended^[5] that New Scientist publish Costella's refutation^[3] of Shawyer's theory paper^[2]. A particle accelerator uses electric fields to propel charged particles to great energies. ... Science fiction is a form of speculative fiction principally dealing with the impact of imagined science and technology, or both, upon society and persons as individuals. ... The term writer can apply to anyone who creates a written work, but the word more usually designates those who write creatively or professionally, or those who have written in many different forms. ... Greg Egan (August 20, 1961, Perth, Western Australia) is an Australian computer programmer and science fiction author. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... Mathematical physics is the scientific field in between mathematics and physics; it studies the problems inspired by physics within a mathematically rigorous framework. ... John Carlos Baez (b. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ...

Analysis

Any claim of a reactionless drive is treated with skepticism by the physics community, since it violates well-established principles such as the conservation of momentum and conservation of energy, both of which have enormous experimental support. A reactionless drive or reactionless thruster (sometimes even reactionless engine) is a hypothetical form of thrust that does not require any outside force to move. ... In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... Conservation of energy states that the total amount of energy in an isolated system remains constant, although it may change forms (for instance, friction turns kinetic energy into thermal energy). ...

Since all phenomena described by standard physical theory necessarily conserve energy, any calculation based on standard physical theory that predicts a violation of energy conservation must be in error. This is a non-controversial and fundamental fact regarding the mathematical structure of the theories, regardless of whether the theories themselves are or are not correct descriptions of the physical world. Accordingly, the results reported regarding the EmDrive, if true, would demonstrate that existing physical theory (or its application in engineering) is incorrect or incomplete.

The EmDrive has been compared to the previous Dean Drive, in that an oscillatory motion is set up so that it has a different effect in each direction of the stroke, in the hope that momentum transfer will differ in each direction, except in this case the oscillations are said to be electromagnetic. The Dean drive or Dean device was invented by Norman L. Dean, who called it a reactionless drive — a mechanical device that could use energy to produce linear acceleration without the use of any reaction mass. ...

Conservation of momentum is also required and maintained in Maxwell's equations, Newtonian mechanics, Special relativity and quantum mechanics (and their combination, quantum electrodynamics), so this claim cannot be valid unless these well-established physical theories are false or can be otherwise explained in terms within these existing theories. In physics, a conservation law states that a particular measurable property of an isolated physical system does not change as the system evolves. ... In electromagnetism, Maxwells equations are a set of equations developed in the latter half of the nineteenth century by James Clerk Maxwell. ... It has been suggested that this article or section be merged with Classical mechanics. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... Fig. ... Quantum electrodynamics (QED) is a relativistic quantum field theory of electromagnetism. ...

Shawyer's calculations^[2] may be in error.^[3] He may have incorrectly identified the forces on the sides of the waveguide. If an error is present, it is most likely that the 'thrust' is eliminated and the drive then cannot accelerate. Despite some criticism Shawyer still claims his machines work.

Any dispute will be settled when independent observations are able to conclude whether or not the machine works in the way it is claimed.

References

Notes

1. ^ ^{a b c} Justin Mullins. "Relativity drive: The end of wings and wheels?", New Scientist, 2006-09-08, pp. 30–34. 
2. ^ ^{a b c} Roger Shawyer (2006). A Theory of Microwave Propulsion for Spacecraft, v.9.3.
3. ^ ^{a b c} John P. Costella (2006). Why Shawyer's 'electromagnetic relativity drive' is a fraud.
4. ^ Tom Shelley. "A force for space with no reaction", Eureka, 2002-12-12. 
5. ^ ^{a b} Greg Egan, A Plea to Save "New Scientist", the n-Category Cafe (a group blog on math, physics and philosophy ), September 19, 2006.

New Scientist is a weekly international science magazine covering recent developments in science and technology for a general English-speaking audience. ... For the Manfred Mann album, see 2006 (album). ... September 8 is the 251st day of the year (252nd in leap years). ... For album titles with the same name, see 2002 (album). ... December 12 is the 346th day (347th in leap years) of the year in the Gregorian calendar, with 19 days remaining. ... September 19 is the 262nd day of the year (263rd in leap years). ... For the Manfred Mann album, see 2006 (album). ...

Other sources

• Roger Shawyer (2006-04-07). "Progress in the Development of a Microwave Engine for Spacecraft Propulsion". British Rocketry Oral History Programme. 
• Roger Shawyer (2005). "The Development of a Microwave Engine for Spacecraft Propulsion". Spaceflight (1). 
• Richard Fisher (2004-11-05). "Defying gravity: UK team claims engine based on microwaves could revolutionise spacecraft propulsion". Engineer 293 (7663): 8. 

For the Manfred Mann album, see 2006 (album). ... April 7 is the 97th day of the year in the Gregorian calendar (98th in leap years). ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... November 5 is the 309th day of the year (310th in leap years) in the Gregorian calendar, with 56 days remaining. ...

See also

• Dean drive
• Momentum
• Perpetual motion
• Reactionless drive

The Dean drive or Dean device was invented by Norman L. Dean, who called it a reactionless drive — a mechanical device that could use energy to produce linear acceleration without the use of any reaction mass. ... In classical mechanics, momentum (pl. ... This article or section should include material from Parallel Path See also Perpetuum mobile as a musical term Perpetual motion machines (the Latin term perpetuum mobile is not uncommon) are a class of hypothetical machines which would produce useful energy in a way science cannot explain (yet). ... A reactionless drive or reactionless thruster (sometimes even reactionless engine) is a hypothetical form of thrust that does not require any outside force to move. ...

External links

• Satellite Propulsion Research, Ltd. (SPR), the website of Roger Shawyer
• "Microwave engine gets a boost", The Engineer Online, 2006-09-01. 
• "EmDrive on trial", New Scientist, 2006-10-03.