Reactionless drive
Encyclopedia
A reactionless drive is a fictional or theorized method of propulsion where thrust
is generated without any need for any outside force or net momentum
exchange to produce linear motion. The name comes from Newton's Third Law of Motion, usually expressed as: "For every action, there is an equal and opposite reaction". Such a drive would necessarily violate the conservation of momentum, a fundamental principle of all current understandings of physics
. In addition it can be shown that conservation of energy
is violated.
In spite of their physical impossibility, such devices are a staple of science fiction
, particularly for space propulsion, and as with perpetual motion
machines have been proposed as working technologies.
drive, internal drive or slip-stick
drive) proposes to use the motion of internal masses to create a net thrust. These thrusters include either vibrational or rotating masses, in which one portion of the cyclical motion is high-speed, and the other low-speed, or alternately high and low impulse. The actual result is that for some of the motion a high force is generated, enough to overcome friction. However on the "return stroke" the force is not high enough, and any motion occurring in the first portion is not reset. In this way the devices "steal" working mass
from their supporting surface, a fact that may not be apparent to casual observation.
Basically, an oscillation thruster works just like walking does, one mass is "thrown" backward, "thrusting" the device forward according to conservation of momentum (like a person taking a step forward), then the mass is more slowly brought forward to its initial position (like the person using their step to pull the rest of their body forward). The thruster is allowed to move forward in the first step because the mass is "thrown" back with large enough force to overcome static friction. The "thruster" doesn't move backward in the second step because static friction provides an outside force that overcomes the step (like the ground does when you're walking).
Although there have been many versions proposed, all oscillation thrusters have the following common components:
A primary feature is that these internal masses go through some sort of cyclic motion where the motion in one direction is quicker than in the return direction.
Inventors of oscillation thrusters extrapolate its behavior to mean that it can work in a vacuum in zero gravity.
One of the most famous proposed reactionless drives was the Dean drive
. Although Dean himself gave few indications of how his "reactionless drive" was supposed to work, it appears to be an attempt at an oscillation thruster. Other examples of oscillation thrusters are the Thornson Inertial Engine and Henry Bull’s Impulse Engine of 1935.
Furthermore, the total energy of the universe becomes reference frame
dependent—energy can only be conserved in the presence of a reactionless drive in (at most) one reference frame, because in all other reference frames the change in kinetic energy of the ship differs from the power expended by the ship. Given that these two laws—the conservation of momentum and the principle of relativity
—are so well established (and thoroughly verified) in physics, any ordinary mechanical system purporting to violate the laws is generally dismissed outright.
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
is generated without any need for any outside force or net momentum
Momentum
In classical mechanics, linear momentum or translational momentum is the product of the mass and velocity of an object...
exchange to produce linear motion. The name comes from Newton's Third Law of Motion, usually expressed as: "For every action, there is an equal and opposite reaction". Such a drive would necessarily violate the conservation of momentum, a fundamental principle of all current understandings of physics
Physics
Physics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
. In addition it can be shown that conservation of energy
Conservation of energy
The nineteenth century law of conservation of energy is a law of physics. It states that the total amount of energy in an isolated system remains constant over time. The total energy is said to be conserved over time...
is violated.
In spite of their physical impossibility, such devices are a staple of science fiction
Science fiction
Science fiction is a genre of fiction dealing with imaginary but more or less plausible content such as future settings, futuristic science and technology, space travel, aliens, and paranormal abilities...
, particularly for space propulsion, and as with perpetual motion
Perpetual motion
Perpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....
machines have been proposed as working technologies.
Oscillation thruster
An oscillation thruster (also known as a stictionStiction
Stiction is the static friction that needs to be overcome to enable relative motion of stationary objects in contact. The term is a portmanteau of the term "static friction", perhaps also influenced by the verb "stick"....
drive, internal drive or slip-stick
Stick-slip phenomenon
The stick-slip phenomenon, also known as the slip-stick phenomenon or simply stick-slip, is the spontaneous jerking motion that can occur while two objects are sliding over each other.- Cause :...
drive) proposes to use the motion of internal masses to create a net thrust. These thrusters include either vibrational or rotating masses, in which one portion of the cyclical motion is high-speed, and the other low-speed, or alternately high and low impulse. The actual result is that for some of the motion a high force is generated, enough to overcome friction. However on the "return stroke" the force is not high enough, and any motion occurring in the first portion is not reset. In this way the devices "steal" working mass
Working mass
Working mass is a mass against which a system operates in order to produce acceleration.In the case of a rocket, for example, the reaction mass is the fuel shot backwards to provide propulsion. All acceleration requires an exchange of momentum, which can be thought of as the "unit of movement"...
from their supporting surface, a fact that may not be apparent to casual observation.
Basically, an oscillation thruster works just like walking does, one mass is "thrown" backward, "thrusting" the device forward according to conservation of momentum (like a person taking a step forward), then the mass is more slowly brought forward to its initial position (like the person using their step to pull the rest of their body forward). The thruster is allowed to move forward in the first step because the mass is "thrown" back with large enough force to overcome static friction. The "thruster" doesn't move backward in the second step because static friction provides an outside force that overcomes the step (like the ground does when you're walking).
Although there have been many versions proposed, all oscillation thrusters have the following common components:
- Chassis to support a system of masses,
- Conveyor that moves the masses through an asymmetric cycle,
- Power source for the conveyor.
A primary feature is that these internal masses go through some sort of cyclic motion where the motion in one direction is quicker than in the return direction.
Inventors of oscillation thrusters extrapolate its behavior to mean that it can work in a vacuum in zero gravity.
One of the most famous proposed reactionless drives was the Dean drive
Dean drive
The Dean drive is a device intended to be a reactionless thruster that was invented by Norman L. Dean. Dean claimed that it was able to generate a uni-directional force, in violation of Newton's Third Law of Motion. Such a violation is generally considered to be impossible in physics...
. Although Dean himself gave few indications of how his "reactionless drive" was supposed to work, it appears to be an attempt at an oscillation thruster. Other examples of oscillation thrusters are the Thornson Inertial Engine and Henry Bull’s Impulse Engine of 1935.
Quantum vacuum
Magnetoelectric materials can be electrically polarized by magnetic fields; the quantum vacuum contains randomly fluctuating magnetic fields. A sufficiently small piece of magnetoelectric material can be placed in the quantum vacuum and then rotated 180 degrees. The random magnetic fields can induce a change in electric polarization in the block of material. It has been proposed that this change causes the combined electric and magnetic fields to push the block in one direction while they (the fields themselves, or more technically, the bosons of which these fields are composed) get pushed in the other direction. The trick doesn't work if the magnetoelectric block is too large but curiously it should work if there's a grid of many tiny blocks working together. This mechanism was first suggested in December 2009 and has not been tested. The author of the original paper suggested that the mechanism could be used would be powerful enough to reorient satellites if a material with a magnetoelectric constant ten times higher than the strongest such materials known today could be found.Physical impossibility
Reactionless drives are impossible as "breaking the law of conservation of momentum shatters the entire mathematical framework" of physics. These devices by their very nature violate the law of conservation of momentum—if a ship with such a drive existed, then any motion of that ship, unaccompanied by the motion of any other material, would cause the center of gravity of the universe to move with it.Furthermore, the total energy of the universe becomes reference frame
Frame of reference
A frame of reference in physics, may refer to a coordinate system or set of axes within which to measure the position, orientation, and other properties of objects in it, or it may refer to an observational reference frame tied to the state of motion of an observer.It may also refer to both an...
dependent—energy can only be conserved in the presence of a reactionless drive in (at most) one reference frame, because in all other reference frames the change in kinetic energy of the ship differs from the power expended by the ship. Given that these two laws—the conservation of momentum and the principle of relativity
Principle of relativity
In physics, the principle of relativity is the requirement that the equations describing the laws of physics have the same form in all admissible frames of reference....
—are so well established (and thoroughly verified) in physics, any ordinary mechanical system purporting to violate the laws is generally dismissed outright.
Alternative approaches
Although the basic tenet of reactionless propulsion is physically impossible, hypothetical cases have been put forward which would create the same effect without evidently violating either Newton's Third Law or conservation of energy:- General relativity allows a hypothetical astronaut to "swim" in curved space without using reaction mass, cf. In other words, if spacetime is flat, then an astronaut can change his or her orientation in space through certain body movements (in the same manner as a falling cat can orient itself so that it hits the ground feet-first), but no amount of this sort of exertion will change the position of his center of mass. However, if local spacetime is curved, a similar trick can be used to take advantage of this curvature; mass held in the astronaut's outstretched hands moves in a slightly different path through curved spacetime than mass at the astronaut's feet, and the resulting "force" on the astronaut can change his position. While this concept is allowed by the currently accepted laws of physics, it is not clear how or even if this effect could provide a useful means of accelerating an actual space vehicle.
- Electrodynamic tetherElectrodynamic tetherElectrodynamic tethers are long conducting wires, such as one deployed from a tether satellite, which can operate on electromagnetic principles as generators, by converting their kinetic energy to electrical energy, or as motors, converting electrical energy to kinetic energy...
s do not expel reaction mass like a rocket; however, as electromagnetic fieldElectromagnetic fieldAn electromagnetic field is a physical field produced by moving electrically charged objects. It affects the behavior of charged objects in the vicinity of the field. The electromagnetic field extends indefinitely throughout space and describes the electromagnetic interaction...
s can carry energy and momentum, tethers do have a mechanism for momentum transfer and hence are not reactionless.
Dean drive
The Dean drive, invented by Norman L. Dean, is a device intended to be a reactionless thruster. According to Dean his models were able to demonstrate this effect. He received two patents for related devices that are known to be unable to generate a uni-directional force, but he occasionally demonstrated devices that were different. Dean's claims of reactionless thrust generation have subsequently been shown to be in error; the thrust generated is understood to be reliant on friction with the surface on which the device is resting.Gyroscopic Inertial Thruster (GIT)
The Gyroscopic Inertial Thruster is a proposed reactionless engine which uses entirely mechanical principles. The concept involves various methods of leverage against the supports of a large gyroscope. Scottish inventor Sandy Kidd, a former RAF radar technician, investigated the possibility without success in the 1980s. He posited that a gyroscope set at various angles could provide a lifting force, defying gravity. In the 1990s, several people sent suggestions to NASA's Space Exploration Outreach Program (SEOP) recommending that NASA study gyroscopic inertial drive, especially the developments of American inventor Robert Cook, and Canadian inventor Roy Thornson. In the '90s and 2000s, enthusiasts attempted building and testing GIT machines.See also
- Abraham-Minkowski controversyAbraham-Minkowski controversyThe Abraham–Minkowski controversy is a physics debate concerning electromagnetic momentum within dielectric media. The preponderance of evidence in the debate suggests that the Abraham equation is correct, but some investigators disagree....
- Beam-powered propulsionBeam-powered propulsionBeam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
- Bernard HaischBernard HaischBernard Haisch is a German-born American astrophysicist who has done research in solar-stellar astrophysics and stochastic electrodynamics. He has developed with Alfonso Rueda a speculative theory that the non-zero lowest energy state of the vacuum, as predicted by quantum mechanics, might provide...
- EmDriveEmDriveEmDrive is the name of a spacecraft propulsion system proposed, and reportedly developed, by Roger Shawyer. New Scientist ran a cover story on EmDrive in its 8 September 2006 issue. The device is a magnetron with a specially shaped, fully enclosed tapering resonator cavity whose area is greater...
- Harold Puthoff
- Inertialess driveInertialess driveThe inertialess drive is a fictional means of accelerating to close to the speed of light or faster-than-light travel, originally used in Triplanetary and the Lensman series by E.E. "Doc" Smith, and later by Robert A...
- Perpetual motionPerpetual motionPerpetual motion describes hypothetical machines that operate or produce useful work indefinitely and, more generally, hypothetical machines that produce more work or energy than they consume, whether they might operate indefinitely or not....
- SpindizzySpindizzyThe Dillon-Wagoner Graviton Polarity Generator, known colloquially as the spindizzy is a fictitious anti-gravity device imagined by James Blish for his series Cities in Flight...
- Stochastic electrodynamicsStochastic electrodynamicsIn theoretical physics, Stochastic Electrodynamics is a variant of Classical Electrodynamics which posits the existence of a classical Lorentz Invariant radiation field having statistical properties similar to that of the electromagnetic zero-point field of Quantum Electrodynamics...
- Woodward effectWoodward effectThe Woodward effect is a hypothesis proposed by James F. Woodward, a physicist at California State University, Fullerton, that energy-storing ions experience transient mass fluctuations when accelerated. While some have expressed doubt about this hypothesis, no respected theoreticians have yet...