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Reactionless Drive
A reactionless drive is a hypothetical device producing motion without the exhaust of a propellant. A propellantless drive is not necessarily reactionless when it constitutes an open system interacting with external fields; but a reactionless drive is a particular case of a propellantless drive that is a closed system, presumably in contradiction with the law of conservation of momentum. Reactionless drives are often considered similar to a perpetual motion machine. The name comes from Newton's third law, often expressed as: "For every action, there is an equal and opposite reaction." Many infeasible reactionless drives are a staple of science fiction for space propulsion. Closed systems Through the years there have been numerous claims for functional reactionless drive designs using ordinary mechanics (i.e., devices not said to be based on quantum mechanics, relativity or atomic forces or effects). Two of these represent their general classes: the Dean drive is perhaps the b ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Motion (physics)
In physics, motion is the phenomenon in which an object changes its position with respect to time. Motion is mathematically described in terms of displacement, distance, velocity, acceleration, speed and frame of reference to an observer and measuring the change in position of the body relative to that frame with change in time. The branch of physics describing the motion of objects without reference to its cause is called kinematics, while the branch studying forces and their effect on motion is called dynamics. If an object is not changing relative to a given frame of reference, the object is said to be ''at rest'', ''motionless'', ''immobile'', '' stationary'', or to have a constant or time-invariant position with reference to its surroundings. Modern physics holds that, as there is no absolute frame of reference, Newton's concept of '' absolute motion'' cannot be determined. As such, everything in the universe can be considered to be in motion. Motion applies to various p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gravity Assist
In orbital mechanics and aerospace engineering, a gravitational slingshot, gravity assist maneuver, or swing-by is the use of the relative movement (e.g. orbit around the Sun) and gravity of a planet or other astronomical object to alter the path and speed of a spacecraft, typically to save propellant and reduce expense. Gravity assistance can be used to accelerate a spacecraft, that is, to increase or decrease its speed or redirect its path. The "assist" is provided by the motion of the gravitating body as it pulls on the spacecraft. Any gain or loss of kinetic energy and velocity by a passing spacecraft is correspondingly lost or gained by the gravitational body, in accordance with Newton's Third Law. The gravity assist maneuver was first used in 1959 when the Soviet probe Luna 3 photographed the far side of Earth's Moon and it was used by interplanetary probes from Mariner 10 onward, including the two Voyager probes' notable flybys of Jupiter and Saturn. Explanation A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Negative Energy
Negative energy is a concept used in physics to explain the nature of certain fields, including the gravitational field and various quantum field effects. Gravitational potential energy Gravitational potential energy can be defined as being negative, but it has no physical meaning since a potential energy is always defined up to a constant. Gravity is a force deriving from a potential, hence, for an object of mass m at P in the field created by a point like object of mass M at O, \vec F_=\frac= -\vec\nabla \Phi(P) Solving this differential equation leads to \Phi(P)= \frac+ K K is often taken equal to 0 so that the potential energy at infinity is 0, then the potential energy is always negative for any distance. There is no physical need for K to be 0, it could be arbitrarily positive. Potential energy should not be confused with the field energy density or its integral, even if related. As two massive objects move towards each other, the motion accelerates under gravity ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Interstellar Travel
Interstellar travel is the hypothetical travel of spacecraft from one star system, solitary star, or planetary system to another. Interstellar travel is expected to prove much more difficult than interplanetary spaceflight due to the vast difference in the scale of the involved distances. Whereas the distance between any two planets in the Solar System is less than 30 astronomical units (AU), stars are typically separated by hundreds of thousands of AU, causing these distances to typically be expressed instead in light-years. Because of the vastness of these distances, non-generational interstellar travel based on known physics would need to occur at a high percentage of the speed of light; even so, travel times would be long, at least decades and perhaps millennia or longer. As of 2022, five uncrewed spacecraft, all launched and operated by the United States, have achieved the escape velocity required to leave the Solar System as part of missions to explore parts of the out ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Faster-than-light
Faster-than-light (also FTL, superluminal or supercausal) travel and communication are the conjectural propagation of matter or information faster than the speed of light (). The special theory of relativity implies that only particles with zero rest mass (i.e., photons) may travel ''at'' the speed of light, and that nothing may travel faster. Particles whose speed exceeds that of light (tachyons) have been hypothesized, but their existence would violate causality and would imply time travel. The scientific consensus is that they do not exist. "Apparent" or "effective" FTL, on the other hand, depends on the hypothesis that unusually distorted regions of spacetime might permit matter to reach distant locations in less time than light could in normal ("undistorted") spacetime. As of the 21st century, according to current scientific theories, matter is required to travel at slower-than-light (also STL or subluminal) speed with respect to the locally distorted spacetime region. Appar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alcubierre Drive
The Alcubierre drive () is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable energy-density field lower than that of vacuum (that is, negative mass) could be created. Proposed by theoretical physicist Miguel Alcubierre in 1994, the Alcubierre drive is based on a solution of Einstein's field equations. Since those solutions are metric tensors, the Alcubierre drive is also referred to as Alcubierre metric. Objects cannot accelerate to the speed of light within normal spacetime; instead, the Alcubierre drive shifts space around an object so that the object would arrive at its destination more quickly than light would in normal space without breaking any physical laws. Although the metric proposed by Alcubierre is consistent with the Einstein field equations, construction of such a drive is not necessarily possible. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
General Relativity
General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. General relativity generalizes special relativity and refines Newton's law of universal gravitation, providing a unified description of gravity as a geometric property of space and time or four-dimensional spacetime. In particular, the ' is directly related to the energy and momentum of whatever matter and radiation are present. The relation is specified by the Einstein field equations, a system of second order partial differential equations. Newton's law of universal gravitation, which describes classical gravity, can be seen as a prediction of general relativity for the almost flat spacetime geometry around stationary mass distributions. Some predictions of general relativity, however, are beyond Newton's law of universal gravitat ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spacetime
In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Spacetime diagrams can be used to visualize relativistic effects, such as why different observers perceive differently where and when events occur. Until the 20th century, it was assumed that the three-dimensional geometry of the universe (its spatial expression in terms of coordinates, distances, and directions) was independent of one-dimensional time. The physicist Albert Einstein helped develop the idea of spacetime as part of his theory of relativity. Prior to his pioneering work, scientists had two separate theories to explain physical phenomena: Isaac Newton's laws of physics described the motion of massive objects, while James Clerk Maxwell's electromagnetic models explained the properties of light. However, in 1905, Einstein based a work on special relativity on two postulates: * The laws of physics are invariant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Alcubierre
Alcubierre is a municipality located in the province of Huesca, Aragon, Spain. According to the 2004 census (INE), the municipality has a population of 439 inhabitants. This town gives its name to the Sierra de Alcubierre Sierra de Alcubierre is a long mountain range in the Monegros comarca, Aragon, Spain. It is located between the provinces of Zaragoza and Huesca. Geography This mountain chain crosses the arid eastern end of the Monegros comarca from northwest t ... (highest point 822 m) that rises in the west, about 3 km away. References External links and further readingChapter 2 Homage to Catalonia by George Orwell (archived link) Municipalities in the Province of Huesca {{huesca-geo-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
RF Resonant Cavity Thruster
The EmDrive is a concept for a thruster for spacecraft, first written about in 2001. It is purported to generate thrust by reflecting microwaves inside the device, in a way that would violate the law of conservation of momentum and other laws of physics. The concept has been referred to at times as a resonant cavity thruster or as the latest Impossible Drive. There is no official design for this device. Neither person who claims to have invented it has committed to an explanation for how it could operate as a thruster or what elements define it, making it hard to say definitively whether a given object is an example of an EmDrive. However, 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, however subsequent studies suggested this was a measurement error caused by thermal gradients. In 2021, Martin Tajmar's group at the Dresden University of ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Woodward Effect
James F. Woodward (born 1941) is a professor emeritus of history and an adjunct professor of physics at California State University, Fullerton. He is best known for a physics hypothesis that he proposed in 1990, later expanded, that predicts several physical effects that he refers to as ' Mach effects'. Woodward claims the effect could be used as a reactionless drive for space travel. Education and professorships * A.B., Middlebury College, 1964, Physics * M.S., New York University, 1969, Physics * Ph.D., University of Denver, 1972, History of science Woodward is a professor emeritus of history and an adjunct professor of physics at California State University, Fullerton. Mach effects Woodward claims that his hypothesis predicts physical forces that he calls ''Mach effects'' but are also referred to as the ''Woodward effect''. He says that his hypothesis is based on Mach's principle that posits inertia, the resistance of mass to acceleration, is a result of the mutual gravit ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The first laser was built in 1960 by Theodore H. Maiman at Hughes Research Laboratories, based on theoretical work by Charles Hard Townes and Arthur Leonard Schawlow. A laser differs from other sources of light in that it emits light which is ''coherent''. Spatial coherence allows a laser to be focused to a tight spot, enabling applications such as laser cutting and lithography. Spatial coherence also allows a laser beam to stay narrow over great distances (collimation), enabling applications such as laser pointers and lidar (light detection and ranging). Lasers can also have high temporal coherence, which allows them to emit light with a very narrow spectrum. Alternatively, temporal coherence can be used to produce ultrashort pulses of ligh ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
