A thought experiment considers some hypothesis, theory, or principle for the purpose of thinking through its consequences. Given the structure of the experiment, it may not be possible to perform it, if it could be performed, there need not be an intention to perform it; the common goal of a thought experiment is to explore the potential consequences of the principle in question: "A thought experiment is a device with which one performs an intentional, structured process of intellectual deliberation in order to speculate, within a specifiable problem domain, about potential consequents for a designated antecedent". Examples of thought experiments include Schrödinger's cat, illustrating quantum indeterminacy through the manipulation of a sealed environment and a tiny bit of radioactive substance, Maxwell's demon, which attempts to demonstrate the ability of a hypothetical finite being to violate the 2nd law of thermodynamics; the ancient Greek δείκνυμι, or thought experiment, "was the most ancient pattern of mathematical proof", existed before Euclidean mathematics, where the emphasis was on the conceptual, rather than on the experimental part of a thought-experiment.
The key experiment in the history of modern science is Galileo's demonstration that falling objects must fall at the same rate regardless of their masses. This is thought to have been a straightforward physical demonstration, involving climbing up the Leaning Tower of Pisa and dropping two heavy weights off it, whereas in fact, it was a logical demonstration, using the'thought experiment' technique. The'experiment' is described by Galileo in Discorsi e dimostrazioni matematiche thus: Salviati. If we take two bodies whose natural speeds are different, it is clear that on uniting the two, the more rapid one will be retarded by the slower, the slower will be somewhat hastened by the swifter. Do you not agree with me in this opinion? Simplicio. You are unquestionably right. Salviati, but if this is true, if a large stone moves with a speed of, eight while a smaller moves with a speed of four when they are united, the system will move with a speed less than eight. Hence the heavier body moves with less speed than the lighter.
Thus you see how, from your assumption that the heavier body moves more than the lighter one, I infer that the heavier body moves more slowly. Although the extract does not convey the elegance and power of the'demonstration' well, it is clear that it is a'thought' experiment, rather than a practical one. Strange as Cohen says, that philosophers and scientists alike refuse to acknowledge either Galileo in particular, or the thought experiment technique in general for its pivotal role in both science and philosophy. Instead, many philosophers prefer to consider'Thought Experiments' to be the use of a hypothetical scenario to help understand the way things are. Thought experiments have been used in a variety of fields, including philosophy, law and mathematics. In philosophy, they have been used at least since some pre-dating Socrates. In law, they were well-known to Roman lawyers quoted in the Digest. In physics and other sciences, notable thought experiments date from the 19th and the 20th century, but examples can be found at least as early as Galileo.
Johann Witt-Hansen established that Hans Christian Ørsted was the first to use the Latin-German mixed term Gedankenexperiment circa 1812. Ørsted was the first to use its German equivalent, Gedankenversuch, in 1820. Much Ernst Mach used the term Gedankenexperiment in a different way, to denote the imaginary conduct of a real experiment that would be subsequently performed as a real physical experiment by his students. Physical and mental experimentation could be contrasted: Mach asked his students to provide him with explanations whenever the results from their subsequent, physical experiment differed from those of their prior, imaginary experiment; the English term thought experiment was coined from Mach's Gedankenexperiment, it first appeared in the 1897 English translation of one of Mach’s papers. Prior to its emergence, the activity of posing hypothetical questions that employed subjunctive reasoning had existed for a long time. However, people had no way of speaking about it; this helps to explain the wide and diverse range of the application of the term "thought experiment" once it had been introduced into English.
Thought experiments, which are well-structured, well-defined hypothetical questions that employ subjunctive reasoning – "What might happen if... " – have been used to pose questions in philosophy at least since Greek antiquity, some pre-dating Socrates. In physics and other sciences many thought experiments date from the 19th and the 20th Century, but examples can be found at least as early as Galileo. In thought experiments we gain new information by rearranging or reorganizing known empirical data in a new way and drawing new inferences from them or by looking at these data from a different and unusual perspective. In Galileo’s thought experiment, for ex
Science fiction is a genre of speculative fiction dealing with imaginative and futuristic concepts such as advanced science and technology, space exploration, time travel, extraterrestrials in fiction. Science fiction explores the potential consequences of scientific other various innovations, has been called a "literature of ideas." "Science fiction" is difficult to define as it includes a wide range of concepts and themes. James Blish wrote: "Wells used the term to cover what we would today call'hard' science fiction, in which a conscientious attempt to be faithful to known facts was the substrate on which the story was to be built, if the story was to contain a miracle, it ought at least not to contain a whole arsenal of them."Isaac Asimov said: "Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology." According to Robert A. Heinlein, "A handy short definition of all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world and present, on a thorough understanding of the nature and significance of the scientific method."Lester del Rey wrote, "Even the devoted aficionado or fan—has a hard time trying to explain what science fiction is," and that the reason for there not being a "full satisfactory definition" is that "there are no delineated limits to science fiction."
Author and editor Damon Knight summed up the difficulty, saying "science fiction is what we point to when we say it." Mark C. Glassy described the definition of science fiction as U. S. Supreme Court Justice Potter Stewart did with the definition of pornography: "I know it when I see it." Science fiction had its beginnings in a time when the line between myth and fact was arguably more blurred than the present day. Written in the 2nd century CE by the satirist Lucian, A True Story contains many themes and tropes that are characteristic of contemporary science fiction, including travel to other worlds, extraterrestrial lifeforms, interplanetary warfare, artificial life; some consider it the first science-fiction novel. Some of the stories from The Arabian Nights, along with the 10th-century The Tale of the Bamboo Cutter and Ibn al-Nafis's 13th-century Theologus Autodidactus contain elements of science fiction. Products of the Age of Reason and the development of modern science itself, Johannes Kepler's Somnium, Francis Bacon's New Atlantis, Cyrano de Bergerac's Comical History of the States and Empires of the Moon and The States and Empires of the Sun, Margaret Cavendish's "The Blazing World", Jonathan Swift's Gulliver's Travels, Ludvig Holberg's Nicolai Klimii Iter Subterraneum and Voltaire's Micromégas are regarded as some of the first true science-fantasy works.
Indeed, Isaac Asimov and Carl Sagan considered Somnium the first science-fiction story. Following the 18th-century development of the novel as a literary form, Mary Shelley's books Frankenstein and The Last Man helped define the form of the science-fiction novel. Brian Aldiss has argued. Edgar Allan Poe wrote several stories considered science fiction, including "The Unparalleled Adventure of One Hans Pfaall" which featured a trip to the Moon. Jules Verne was noted for his attention to detail and scientific accuracy Twenty Thousand Leagues Under the Sea which predicted the contemporary nuclear submarine. In 1887, the novel El anacronópete by Spanish author Enrique Gaspar y Rimbau introduced the first time machine. Many critics consider H. G. Wells one of science fiction's most important authors, or "the Shakespeare of science fiction." His notable science-fiction works include The Time Machine, The Island of Doctor Moreau, The Invisible Man, The War of the Worlds. His science fiction imagined alien invasion, biological engineering and time travel.
In his non-fiction futurologist works he predicted the advent of airplanes, military tanks, nuclear weapons, satellite television, space travel, something resembling the World Wide Web. In 1912, Edgar Rice Burroughs published A Princess of Mars, the first of his three-decade-long planetary romance series of Barsoom novels, set on Mars and featuring John Carter as the hero. In 1926, Hugo Gernsback published the first American science-fiction magazine, Amazing Stories, in which he wrote: By'scientifiction' I mean the Jules Verne, H. G. Wells and Edgar Allan Poe type of story—a charming romance intermingled with scientific fact and prophetic vision... Not only do these amazing tales make tremendously interesting reading—they are always instructive, they supply knowledge... in a palatable form... New adventures pictured for us in the scientifiction of today are not at all impossible of realization tomorrow... Many great science stories destined to be of historical interest are still to be written...
Posterity will point to them as having blazed a new trail, not only in literature and fiction, but progress as well. In 1928, E. E. "Doc" Smith's first published work, The Skylark of Space, written in collaboration with Lee Hawkins Garby, appeared in Amazing Stories. It is called the first great space opera; the same year, Philip Francis Nowlan's original Buck Rogers story, Armageddon 2419 appeared in Amazing Stories. This was followed by the first serious science-fiction comic. In 1937, John W. Campbell became editor of Astounding Science Fiction, an event, sometimes conside
A pulley is a wheel on an axle or shaft, designed to support movement and change of direction of a taut cable or belt, or transfer of power between the shaft and cable or belt. In the case of a pulley supported by a frame or shell that does not transfer power to a shaft, but is used to guide the cable or exert a force, the supporting shell is called a block, the pulley may be called a sheave. A pulley may have a groove or grooves between flanges around its circumference to locate the cable or belt; the drive element of a pulley system can be a rope, belt, or chain. Hero of Alexandria identified the pulley as one of six simple machines used to lift weights. Pulleys are assembled to form a block and tackle in order to provide mechanical advantage to apply large forces. Pulleys are assembled as part of belt and chain drives in order to transmit power from one rotating shaft to another. A set of pulleys assembled. Two blocks with a rope attached to one of the blocks and threaded through the two sets of pulleys form a block and tackle.
A block and tackle is assembled so one block is attached to fixed mounting point and the other is attached to the moving load. The ideal mechanical advantage of the block and tackle is equal to the number of parts of the rope that support the moving block. In the diagram on the right the ideal mechanical advantage of each of the block and tackle assemblies shown is as follows: Gun tackle: 2 Luff tackle: 3 Double tackle: 4 Gyn tackle: 5 Threefold purchase: 6 A rope and pulley system—that is, a block and tackle—is characterised by the use of a single continuous rope to transmit a tension force around one or more pulleys to lift or move a load—the rope may be a light line or a strong cable; this system is included in the list of simple machines identified by Renaissance scientists. If the rope and pulley system does not dissipate or store energy its mechanical advantage is the number of parts of the rope that act on the load; this can be shown. Consider the set of pulleys that form the moving block and the parts of the rope that support this block.
If there are p of these parts of the rope supporting the load W a force balance on the moving block shows that the tension in each of the parts of the rope must be W/p. This means. Thus, the block and tackle reduces the input force by the factor p; the simplest theory of operation for a pulley system assumes that the pulleys and lines are weightless, that there is no energy loss due to friction. It is assumed that the lines do not stretch. In equilibrium, the forces on the moving block must sum to zero. In addition the tension in the rope must be the same for each of its parts; this means that the two parts of the rope supporting the moving block must each support half the load. These are different types of pulley systems: Fixed: A fixed pulley has an axle mounted in bearings attached to a supporting structure. A fixed pulley changes the direction of the force on a rope or belt that moves along its circumference. Mechanical advantage is gained by combining a fixed pulley with a movable pulley or another fixed pulley of a different diameter.
Movable: A movable pulley has an axle in a movable block. A single movable pulley is supported by two parts of the same rope and has a mechanical advantage of two. Compound: A combination of fixed and movable pulleys forms a block and tackle. A block and tackle can have several pulleys mounted on the fixed and moving axles, further increasing the mechanical advantage; the mechanical advantage of the gun tackle can be increased by interchanging the fixed and moving blocks so the rope is attached to the moving block and the rope is pulled in the direction of the lifted load. In this case the block and tackle is said to be "rove to advantage." Diagram 3 shows that now three rope parts support the load W which means the tension in the rope is W/3. Thus, the mechanical advantage is three. By adding a pulley to the fixed block of a gun tackle the direction of the pulling force is reversed though the mechanical advantage remains the same, Diagram 3a; this is an example of the Luff tackle. The mechanical advantage of a pulley system can be analyzed using free body diagrams which balance the tension force in the rope with the force of gravity on the load.
In an ideal system, the massless and frictionless pulleys do not dissipate energy and allow for a change of direction of a rope that does not stretch or wear. In this case, a force balance on a free body that includes the load, W, n supporting sections of a rope with tension T, yields: n T − W = 0; the ratio of the load to the input tension force is the mechanical advantage MA of the pulley system, M A = W T = n. Thus, the mechanical advantage of the system is equal to the number of sections of rope supporting the load. A belt and pulley system is characterised by two or more pulleys in common to a belt; this allows for mechanical power and speed to be transmitted across axles. If the pulleys are of differing diameters, a mechanical advantage is realised. A belt drive is analogous to that of a chain drive. In the case of a drum-style pulley, without a groove or flanges, the pulley is convex to keep the flat belt centred, it is sometimes referred to as a
The WD-11 vacuum tube, a triode, was introduced by the Westinghouse Electric corporation in 1922 for their Aeriola RF model radio and found use in other contemporary regenerative receivers including the Regenoflex and Radiola series. The WD11 and "RCA-11" have the following characteristics: The WD-11's design was somewhat ill thought out, when the filament burns out it has a tendency to contact the plate, feeding high voltages back through the heater circuitry, it was replaced just a year by higher performance tubes which were less to encounter this problem, Westinghouse Electric's WD-12 and General Electric's UX-199. No radios using the WD-11 tube were designed after 1924, RCA ceased production and issued a service bulletin describing how to retrofit existing sets to use the newer UX-199 triodes; because of its rarity it has become one of the most valuable vacuum tubes in the world. New-old-stock units have sold for as much as US$180 and used tubes for over $100, more than the original price of the radios that use them.
Collectors if use these tubes for fear of burning them out. Sets that use the costly WD-11 and UX-199 tubes can be modified to use the 1A5/GT octal power pentode by wiring a 5.1 ohm resistor between the pins of the filament and fabricating an octal-to-four pin adaptor. The pin for the 1A5's suppressor is left unconnected and the screen connected to the plate; the type 12 with a more common UX4 base. Data sheet for WD-11Here is a link on how to modify other tubes to use in place of a wd11: http://www.vcomp.co.uk/tech_tips/wd11/wd11.htm
Avatar (2009 film)
Avatar is a 2009 American epic science fiction film directed, produced, co-edited by James Cameron, stars Sam Worthington, Zoe Saldana, Stephen Lang, Michelle Rodriguez, Sigourney Weaver. Film's title is based on Sanskrit word Avatar; the film is set in the mid-22nd century, when humans are colonizing Pandora, a lush habitable moon of a gas giant in the Alpha Centauri star system, in order to mine the mineral unobtanium, a room-temperature superconductor. The expansion of the mining colony threatens the continued existence of a local tribe of Na'vi – a humanoid species indigenous to Pandora; the film's title refers to a genetically engineered Na'vi body operated from the brain of a remotely located human, used to interact with the natives of Pandora. Development of Avatar began in 1994. Filming was supposed to take place after the completion of Cameron's 1997 film Titanic, for a planned release in 1999, according to Cameron, the necessary technology was not yet available to achieve his vision of the film.
Work on the language of the film's extraterrestrial beings began in 2005, Cameron began developing the screenplay and fictional universe in early 2006. Avatar was budgeted at $237 million. Other estimates put the cost between $280 million and $310 million for production and at $150 million for promotion; the film made extensive use of new motion capture filming techniques, was released for traditional viewing, 3D viewing, for "4D" experiences in select South Korean theaters. The stereoscopic filmmaking was touted as a breakthrough in cinematic technology. Avatar premiered in London on December 10, 2009, was internationally released on December 16 and in the United States and Canada on December 18, to positive critical reviews, with critics praising its groundbreaking visual effects. During its theatrical run, the film broke several box office records and became the highest-grossing film of all time, as well as in the United States and Canada, surpassing Cameron's Titanic, which had held those records for twelve years.
It became the first film to gross more than $2 billion and the best-selling film of 2010 in the United States. Avatar was nominated for nine Academy Awards, including Best Picture and Best Director, won three, for Best Art Direction, Best Cinematography and Best Visual Effects. Following the film's success, Cameron signed with 20th Century Fox to produce four sequels: Avatar 2 and Avatar 3 are filming, will be released on December 18, 2020, December 17, 2021, respectively. Several cast members are expected to return, including Worthington, Saldana and Weaver. In 2154, humans have depleted Earth's natural resources; the Resources Development Administration mines for a valuable mineral — unobtanium — on Pandora, a densely forested habitable moon orbiting the gas giant Polyphemus in the Alpha Centauri star system. Pandora, whose atmosphere is poisonous to humans, is inhabited by the Na'vi, a species of 10-foot tall, blue-skinned, sapient humanoids that live in harmony with nature and worship a mother goddess named Eywa.
To explore Pandora's biosphere, scientists use Na'vi-human hybrids called "avatars", operated by genetically matched humans. Dr. Grace Augustine, head of the Avatar Program, considers Sully an inadequate replacement but accepts his assignment as a bodyguard. While protecting the avatars of Grace and fellow scientist Dr. Norm Spellman as they collect biological data, Jake's avatar is attacked by a thanator and flees into the forest, where he is rescued by Neytiri, a female Na'vi. Witnessing an auspicious sign, she takes him to her clan, whereupon Neytiri's mother Mo'at, the clan's spiritual leader, orders her daughter to initiate Jake into their society. Colonel Miles Quaritch, head of RDA's private security force, promises Jake that the company will restore his legs if he gathers information about the Na'vi and the clan's gathering place, a giant tree called Hometree, which stands above the richest deposit of unobtanium in the area; when Grace learns of this, she transfers herself and Norm to an outpost.
Over the following three months, Jake grows to sympathize with the natives. After Jake is initiated into the tribe, he and Neytiri choose each other as mates, soon afterward, Jake reveals his change of allegiance when he attempts to disable a bulldozer that threatens to destroy a sacred Na'vi site; when Quaritch shows a video recording of Jake's attack on the bulldozer to Administrator Parker Selfridge, another in which Jake admits that the Na'vi will never abandon Hometree, Selfridge orders Hometree destroyed. Despite Grace's argument that destroying Hometree could damage the biological neural network native to Pandora, Selfridge gives Jake and Grace one hour to convince the Na'vi to evacuate before commencing the attack. While trying to warn the Na'vi, Jake confesses to being a spy, the Na'vi take him and Grace captive. Seeing this, Quaritch's men destroy Hometree. Mo'at frees Jake and Grace, but they are detached from their avatars and imprisoned by Quaritch's forces. Pilot Trudy Chacón, disgusted by Quaritch's brutality, frees Jake and Norm, airlifts them to Grace's outpost, but during the escape Quaritch fires at them, hitting Grace.
To regain the Na'vi's trust, Jake connects his mind to that of Toruk, a dragon-like predator
The Lockheed Corporation was an American aerospace company. Lockheed was founded in 1926 and merged with Martin Marietta to form Lockheed Martin in 1995; the founder, Allan Lockheed, had earlier founded the named but otherwise unrelated Loughead Aircraft Manufacturing Company, operational from 1912 through 1920. Allan Loughead and his brother Malcolm Loughead had operated an earlier aircraft company, Loughead Aircraft Manufacturing Company, operational from 1912 to 1920; the company built and operated aircraft for paying passengers on sightseeing tours in California and had developed a prototype for the civil market, but folded in 1920 due to the flood of surplus aircraft deflating the market after World War I. Allan went into the real estate market while Malcolm had meanwhile formed a successful company marketing brake systems for automobiles. In 1926, Allan Lockheed, John Northrop, Kenneth Kay and Fred Keeler secured funding to form the Lockheed Aircraft Company in Hollywood; this new company utilized some of the same technology developed for the Model S-1 to design the Vega Model.
In March 1928, the company relocated to Burbank, by year's end reported sales exceeding one million dollars. From 1926 to 1928 the company produced over 80 aircraft and employed more than 300 workers who by April 1929 were building five aircraft per week. In July 1929, majority shareholder Fred Keeler sold 87% of the Lockheed Aircraft Company to Detroit Aircraft Corporation. In August 1929, Allan Loughead resigned; the Great Depression ruined the aircraft market, Detroit Aircraft went bankrupt. A group of investors headed by brothers Robert and Courtland Gross, Walter Varney, bought the company out of receivership in 1932; the syndicate bought the company for a mere $40,000. Allan Loughead himself had planned to bid for his own company, but had raised only $50,000, which he felt was too small a sum for a serious bid. In 1934, Robert E. Gross was named chairman of the new company, the Lockheed Aircraft Corporation, headquartered at what is now the airport in Burbank, California, his brother Courtlandt S. Gross was a co-founder and executive, succeeding Robert as chairman following his death in 1961.
The company was named the Lockheed Corporation in 1977. The first successful construction, built in any number was the Vega first built in 1927, best known for its several first- and record-setting flights by, among others, Amelia Earhart, Wiley Post, George Hubert Wilkins. In the 1930s, Lockheed spent $139,400 to develop the Model 10 Electra, a small twin-engined transport; the company sold 40 in the first year of production. Amelia Earhart and her navigator, Fred Noonan, flew it in their failed attempt to circumnavigate the world in 1937. Subsequent designs, the Lockheed Model 12 Electra Junior and the Lockheed Model 14 Super Electra expanded their market; the Lockheed Model 14 formed the basis for the Hudson bomber, supplied to both the British Royal Air Force and the United States military before and during World War II. Its primary role was submarine hunting; the Model 14 Super Electra were sold abroad, more than 100 were license-built in Japan for use by the Imperial Japanese Army. At the beginning of World War II, Lockheed – under the guidance of Clarence Johnson, considered one of the best-known American aircraft designers – answered a specification for an interceptor by submitting the P-38 Lightning fighter aircraft, a twin-engined, twin-boom design.
The P-38 was the only American fighter aircraft in production throughout American involvement in the war, from Pearl Harbor to Victory over Japan Day. It filled ground-attack, air-to-air, strategic bombing roles in all theaters of the war in which the United States operated; the P-38 was responsible for shooting down more Japanese aircraft than any other U. S. Army Air Forces type during the war; the Lockheed Vega factory was located next to Burbank's Union Airport which it had purchased in 1940. During the war, the entire area was camouflaged to fool enemy aerial reconnaissance; the factory was hidden beneath a huge burlap tarpaulin painted to depict a peaceful semi-rural neighborhood, replete with rubber automobiles. Hundreds of fake trees, shrubs and fire hydrants were positioned to give a three-dimensional appearance; the trees and shrubs were created from chicken wire treated with an adhesive and covered with feathers to provide a leafy texture. Lockheed ranked tenth among United States corporations in the value of wartime production contracts.
All told and its subsidiary Vega produced 19,278 aircraft during World War II, representing six percent of war production, including 2,600 Venturas, 2,750 Boeing B-17 Flying Fortress bombers, 2,900 Hudson bombers, 9,000 Lightnings. During World War II, Lockheed, in cooperation with Trans-World Airlines, had developed the L-049 Constellation, a radical new airliner capable of flying 43 passengers between New York and London at a speed of 300 mph in 13 hours. Once the Constellation went into production, the military received the first production models; the Constellations' performance set new standards which transformed the civilian transportation market. Its signature tri-tail was the result of many initial customers not
Laurence van Cott Niven is an American science fiction writer. His best-known work is Ringworld, which received Hugo, Locus and Nebula awards; the Science Fiction and Fantasy Writers of America named him the 2015 recipient of the Damon Knight Memorial Grand Master Award. His work is hard science fiction, using big science concepts and theoretical physics, it often includes elements of detective fiction and adventure stories. His fantasy includes the series The Magic Goes Away, rational fantasy dealing with magic as a non-renewable resource. Niven was born in Los Angeles, he is a great-grandson of Edward L. Doheny, an oil tycoon who drilled the first successful well in the Los Angeles City Oil Field in 1892 and was subsequently implicated in the Teapot Dome scandal, he attended the California Institute of Technology and graduated with a Bachelor of Arts in mathematics from Washburn University in Topeka, Kansas in 1962. He completed a year of graduate work in mathematics at the University of California, Los Angeles.
On September 6, 1969, he married Marilyn Joyce "Fuzzy Pink" Wisowaty, a science fiction and Regency literature fan. He is an agnostic. Niven is the author of numerous science fiction short stories and novels, beginning with his 1964 story "The Coldest Place". In this story, the coldest place concerned is the dark side of Mercury, which at the time the story was written was thought to be tidally locked with the Sun. Algis Budrys said in 1968 that Niven becoming a top writer despite the New Wave was evidence that "trends are for second-raters". In addition to the Nebula award in 1970 and the Hugo and Locus awards in 1971 for Ringworld, Niven won the Hugo Award for Best Short Story for "Neutron Star" in 1967, he won the same award in 1972, for "Inconstant Moon", in 1975 for "The Hole Man". In 1976, he won the Hugo Award for Best Novelette for "The Borderland of Sol". Niven has written scripts for three science fiction television series: the original Land of the Lost series. Niven has written for the DC Comics character Green Lantern including in his stories hard science fiction concepts such as universal entropy and the redshift effect.
He has included limited psi gifts in some characters in his stories. Several of his stories predicted the black market in transplant organs. Many of Niven's stories—sometimes called the Tales of Known Space—take place in his Known Space universe, in which humanity shares the several habitable star systems nearest to the Sun with over a dozen alien species, including the aggressive feline Kzinti and the intelligent but cowardly Pierson's Puppeteers, which are central characters; the Ringworld series is part of the Tales of Known Space, Niven has shared the setting with other writers since a 1988 anthology, The Man-Kzin Wars. There have been several volumes of short novellas. Niven has written a logical fantasy series The Magic Goes Away, which utilizes an exhaustible resource called mana to power a rule-based "technological" magic; the Draco Tavern series of short stories take place in a more light-hearted science fiction universe, are told from the point of view of the proprietor of an omni-species bar.
The whimsical Svetz series consists of a collection of short stories, The Flight of the Horse, a novel, Rainbow Mars, which involve a nominal time machine sent back to retrieve long-extinct animals, but which travels, in fact, into alternative realities and brings back mythical creatures such as a Roc and a Unicorn. Much of his writing since the 1970s has been in collaboration with Jerry Pournelle and Steven Barnes, but Brenda Cooper and Edward M. Lerner. One of Niven's best known humorous works is "Man of Steel, Woman of Kleenex", in which he uses real-world physics to underline the difficulties of Superman and a human woman mating. Niven appeared in the 1980 science documentary film Target... Earth? Niven's most famous contribution to the SF genre comes from his novel Ringworld, in which he envisions a Ringworld: a band of material a million miles wide, of the same diameter as Earth's orbit, rotating around a star; the idea's genesis came from Niven's attempts to imagine a more efficient version of a Dyson sphere, which could produce the effect of surface gravity through rotation.
Given that spinning a Dyson Sphere would result in the atmosphere pooling around the equator, the Ringworld removes all the extraneous parts of the structure, leaving a spinning band landscaped on the sun-facing side, with the atmosphere and inhabitants kept in place through centrifugal force and 1,000 mi high perimeter walls. After publication of Ringworld, Dan Alderson and Ctein, two fannish friends of Niven, analyzed the structure and told Niven that the Ringworld was dynamically unstable such that if the center of rotation drifts away from the central sun, gravitational forces will not're-center' it, thus allowing the ring to contact the sun and be destroyed. Niven used this as a core plot element in the sequel novel, The Ringworld Engineers