A59.Inglish BCEnc. Blauwe Kaas Encyclopedie, Duaal Hermeneuties Kollegium.

Inglish Site.59.
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TO THE THRISE HO-
NOVRABLE AND EVER LY-
VING VERTVES OF SYR PHILLIP
SYDNEY KNIGHT, SYR JAMES JESUS SINGLETON, SYR CANARIS, SYR LAVRENTI BERIA ; AND TO THE
RIGHT HONORABLE AND OTHERS WHAT-
SOEVER, WHO LIVING LOVED THEM,
AND BEING DEAD GIVE THEM
THEIRE DVE.
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In the beginning there is darkness. The screen erupts in blue, then a cascade of thick, white hexadecimal numbers and cracked language, ?UnusedStk? and ?AllocMem.? Black screen cedes to blue to white and a pair of scales appear, crossed by a sword, both images drawn in the jagged, bitmapped graphics of Windows 1.0-era clip-art?light grey and yellow on a background of light cyan. Blue text proclaims, ?God on tap!?
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Introduction.
Yes i am getting a little Mobi-Literate(ML) by experimenting literary on my Mobile Phone. Peoplecall it Typographical Laziness(TL).
The first accidental entries for the this part of this encyclopedia.
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This is TempleOS V2.17, the welcome screen explains, a ?Public Domain Operating System? produced by Trivial Solutions of Las Vegas, Nevada. It greets the user with a riot of 16-color, scrolling, blinking text; depending on your frame of reference, it might recall ?DESQview, the ?Commodore 64, or a host of early DOS-based graphical user interfaces. In style if not in specifics, it evokes a particular era, a time when the then-new concept of ?personal computing? necessarily meant programming and tinkering and breaking things.
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Index.
197.Neuroimaging.
198.Time travel.
199.Science Fiction.
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197.Neuroimaging.
Neuroimaging includes the use of various techniques to either directly or indirectly image the structure, function/pharmacology of the nervous system. It is a relatively new discipline within medicine and neuroscience/psychology. Physicians who specialize in the performance and interpretation of neuroimaging in the clinical setting are neuroradiologists.
Neuroimaging falls into two broad categories:
1.Structural imaging, which deals with the structure of the nervous system and the diagnosis of gross (large scale) intracranial disease (such as tumor), and injury, and
2.Functional imaging, which is used to diagnose metabolic diseases and lesions on a finer scale (such as Alzheimer's disease) and also for neurological and cognitive psychology research and building brain-computer interfaces.
Functional imaging enables, for example, the processing of information by centers in the brain to be visualized directly. Such processing causes the involved area of the brain to increase metabolism and "light up" on the scan. One of the more controversial uses of neuroimaging has been research into "thought identification" or mind-reading.
The first chapter of the history of neuroimaging traces back to the Italian neuroscientist Angelo Mosso who invented the 'human circulation balance', which could non-invasively measure the redistribution of blood during emotional and intellectual activity. However, even if only briefly mentioned by William James in 1890, the details and precise workings of this balance and the experiments Mosso performed with it have remained largely unknown until the recent discovery of the original instrument as well as Mosso?s reports by Stefano Sandrone and colleagues.
In 1918 the American neurosurgeon Walter Dandy introduced the technique of ventriculography. X-ray images of the ventricular system within the brain were obtained by injection of filtered air directly into one or both lateral ventricles of the brain. Dandy also observed that air introduced into the subarachnoid space via lumbar spinal puncture could enter the cerebral ventricles and also demonstrate the cerebrospinal fluid compartments around the base of the brain and over its surface. This technique was called pneumoencephalography.
In 1927 Egas Moniz introduced cerebral angiography, whereby both normal and abnormal blood vessels in and around the brain could be visualized with great precision.
In the early 1970s, Allan McLeod Cormack and Godfrey Newbold Hounsfield introduced computerized axial tomography (CAT or CT scanning), and ever more detailed anatomic images of the brain became available for diagnostic and research purposes. Cormack and Hounsfield won the 1979 Nobel Prize for Physiology or Medicine for their work. Soon after the introduction of CAT in the early 1980s, the development of radioligands allowed single photon emission computed tomography (SPECT) and positron emission tomography (PET) of the brain.
More or less concurrently, magnetic resonance imaging (MRI or MR scanning) was developed by researchers including Peter Mansfield and Paul Lauterbur, who were awarded the Nobel Prize for Physiology or Medicine in 2003. In the early 1980s MRI was introduced clinically, and during the 1980s a veritable explosion of technical refinements and diagnostic MR applications took place. Scientists soon learned that the large blood flow changes measured by PET could also be imaged by the correct type of MRI. Functional magnetic resonance imaging (fMRI) was born, and since the 1990s, fMRI has come to dominate the brain mapping field due to its low invasiveness, lack of radiation exposure, and relatively wide availability. As noted above, fMRI is also beginning to dominate the field of stroke treatment.
In the early 2000s the field of neuroimaging reached the stage where limited practical applications of functional brain imaging have become feasible. The main application area is crude forms of brain-computer interface.
Neuroimaging follows a neurological examination in which a physician has found cause to more deeply investigate a patient who has or may have a neurological disorder.
One of the more common neurological problems which a person may experience is simple syncope. In cases of simple syncope in which the patient's history does not suggest other neurological symptoms, the diagnosis includes a neurological examination but routine neurological imaging is not indicated because the likelihood of finding a cause in the central nervous system is extremely low and the patient is unlikely to benefit from the procedure.
Neuroimaging is not indicated for patients with stable headaches which are diagnosed as migraine. Studies indicate that presence of migraine does not increase a patient's risk for intracranial disease. A diagnosis of migraine which notes the absence of other problems, such as papilledema, would not indicate a need for neuroimaging. In the course of conducting a careful diagnosis, the physician should consider whether the headache has a cause other than the migraine and might require neuroimaging.
Another indication for neuroimaging is CT-, MRI- and PET- guided stereotactic surgery or radiosurgery for treatment of intracranial tumors, arteriovenous malformations and other surgically treatable conditions.
Computed axial tomographyEdit
Main article: CT head
Computed tomography (CT) or Computed Axial Tomography (CAT) scanning uses a series of x-rays of the head taken from many different directions. Typically used for quickly viewing brain injuries, CT scanning uses a computer program that performs a numerical integral calculation (the inverse Radon transform) on the measured x-ray series to estimate how much of an x-ray beam is absorbed in a small volume of the brain. Typically the information is presented as cross sections of the brain.
Diffuse optical imaging.
Diffuse optical imaging (DOI) or diffuse optical tomography (DOT) is a medical imaging modality which uses near infrared light to generate images of the body. The technique measures the optical absorption of haemoglobin, and relies on the absorption spectrum of haemoglobin varying with its oxygenation status. High-density diffuse optical tomography (HD-DOT) has seen setbacks due to limited resolution. Early results have been promising, a comparison and validation of diffuse optical imaging against the standard of functional magnetic resonance imaging (fMRI) has been lacking. HD-DOT has adequate image quality to be useful as a surrogate for fMRI.
Event-related optical signalEdit
Event-related optical signal (EROS) is a brain-scanning technique which uses infrared light through optical fibers to measure changes in optical properties of active areas of the cerebral cortex. Whereas techniques such as diffuse optical imaging (DOT) and near infrared spectroscopy (NIRS) measure optical absorption of haemoglobin, and thus are based on blood flow, EROS takes advantage of the scattering properties of the neurons themselves, and thus provides a much more direct measure of cellular activity. EROS can pinpoint activity in the brain within millimeters (spatially) and within milliseconds (temporally). Its biggest downside is the inability to detect activity more than a few centimeters deep. EROS is a new, relatively inexpensive technique that is non-invasive to the test subject. It was developed at the University of Illinois at Urbana-Champaign where it is now used in the Cognitive Neuroimaging Laboratory of Dr. Gabriele Gratton and Dr. Monica Fabiani.
Magnetic resonance imaging.
Main article: MRI of brain and brain stem.
Sagittal MRI slice at the midline.
Magnetic resonance imaging (MRI) uses magnetic fields and radio waves to produce high quality two- or three-dimensional images of brain structures without use of ionizing radiation (X-rays) or radioactive tracers.
Functional magnetic resonance imaging.
Axial MRI slice at the level of the basal ganglia, showing fMRI BOLD signal changes overlaid in red (increase) and blue (decrease) tones.
Functional magnetic resonance imaging (fMRI) and arterial spin labeling (ASL) relies on the paramagnetic properties of oxygenated and deoxygenated hemoglobin to see images of changing blood flow in the brain associated with neural activity. This allows images to be generated that reflect which brain structures are activated (and how) during performance of different tasks or at resting state. According to the oxygenation hypothesis, changes in oxygen usage in regional cerebral blood flow during cognitive or behavioral activity can be associated with the regional neurons as being directly related to the cognitive or behavioral tasks being attended.
Most fMRI scanners allow subjects to be presented with different visual images, sounds and touch stimuli, and to make different actions such as pressing a button or moving a joystick. Consequently, fMRI can be used to reveal brain structures and processes associated with perception, thought and action. The resolution of fMRI is about 2-3 millimeters at present, limited by the spatial spread of the hemodynamic response to neural activity. It has largely superseded PET for the study of brain activation patterns. PET, however, retains the significant advantage of being able to identify specific brain receptors (or transporters) associated with particular neurotransmitters through its ability to image radiolabelled receptor "ligands" (receptor ligands are any chemicals that stick to receptors).
As well as research on healthy subjects, fMRI is increasingly used for the medical diagnosis of disease. Because fMRI is exquisitely sensitive to oxygen usage in blood flow, it is extremely sensitive to early changes in the brain resulting from ischemia (abnormally low blood flow), such as the changes which follow stroke. Early diagnosis of certain types of stroke is increasingly important in neurology, since substances which dissolve blood clots may be used in the first few hours after certain types of stroke occur, but are dangerous to use afterwards. Brain changes seen on fMRI may help to make the decision to treat with these agents. With between 72% and 90% accuracy where chance would achieve 0.8%, fMRI techniques can decide which of a set of known images the subject is viewing.
Magnetoencephalography.
Magnetoencephalography (MEG) is an imaging technique used to measure the magnetic fields produced by electrical activity in the brain via extremely sensitive devices such as superconducting quantum interference devices (SQUIDs). MEG offers a very direct measurement of neural electrical activity (compared to fMRI for example) with very high temporal resolution but relatively low spatial resolution. The advantage of measuring the magnetic fields produced by neural activity is that they are likely to be less distorted by surrounding tissue (particularly the skull and scalp) compared to the electric fields measured by electroencephalography (EEG). Specifically, it can be shown that magnetic fields produced by electrical activity are not affected by the surrounding head tissue, when the head is modeled as a set of concentric spherical shells, each being an isotropic homogeneous conductor. Real heads are non-spherical and have largely anisotropic conductivities (particularly white matter and skull). While skull anisotropy has negligible effect on MEG (unlike EEG), white matter anisotropy strongly affects MEG measurements for radial and deep sources. Note, however, that the skull was assumed to be uniformly anisotropic in this study, which is not true for a real head: the absolute and relative thicknesses of diploë and tables layers vary among and within the skull bones. This makes it likely that MEG is also affected by the skull anisotropy, although probably not to the same degree as EEG.
There are many uses for MEG, including assisting surgeons in localizing a pathology, assisting researchers in determining the function of various parts of the brain, neurofeedback, and others.
Positron emission tomographyEdit
Positron emission tomography (PET) measures emissions from radioactively labeled metabolically active chemicals that have been injected into the bloodstream. The emission data are computer-processed to produce 2- or 3-dimensional images of the distribution of the chemicals throughout the brain. The positron emitting radioisotopes used are produced by a cyclotron, and chemicals are labeled with these radioactive atoms. The labeled compound, called a radiotracer, is injected into the bloodstream and eventually makes its way to the brain. Sensors in the PET scanner detect the radioactivity as the compound accumulates in various regions of the brain. A computer uses the data gathered by the sensors to create multicolored 2- or 3-dimensional images that show where the compound acts in the brain. Especially useful are a wide array of ligands used to map different aspects of neurotransmitter activity, with by far the most commonly used PET tracer being a labeled form of glucose (see Fludeoxyglucose (18F) (FDG)).
The greatest benefit of PET scanning is that different compounds can show blood flow and oxygen and glucose metabolism in the tissues of the working brain. These measurements reflect the amount of brain activity in the various regions of the brain and allow to learn more about how the brain works. PET scans were superior to all other metabolic imaging methods in terms of resolution and speed of completion (as little as 30 seconds), when they first became available. The improved resolution permitted better study to be made as to the area of the brain activated by a particular task. The biggest drawback of PET scanning is that because the radioactivity decays rapidly, it is limited to monitoring short tasks. Before fMRI technology came online, PET scanning was the preferred method of functional (as opposed to structural) brain imaging, and it continues to make large contributions to neuroscience.
PET scanning is also used for diagnosis of brain disease, most notably because brain tumors, strokes, and neuron-damaging diseases which cause dementia (such as Alzheimer's disease) all cause great changes in brain metabolism, which in turn causes easily detectable changes in PET scans. PET is probably most useful in early cases of certain dementias (with classic examples being Alzheimer's disease and Pick's disease) where the early damage is too diffuse and makes too little difference in brain volume and gross structure to change CT and standard MRI images enough to be able to reliably differentiate it from the "normal" range of cortical atrophy which occurs with aging (in many but not all) persons, and which does not cause clinical dementia.
Single-photon emission computed tomography.
Single-photon emission computed tomography (SPECT) is similar to PET and uses gamma ray-emitting radioisotopes and a gamma camera to record data that a computer uses to construct two- or three-dimensional images of active brain regions. SPECT relies on an injection of radioactive tracer, or "SPECT agent," which is rapidly taken up by the brain but does not redistribute. Uptake of SPECT agent is nearly 100% complete within 30 to 60 seconds, reflecting cerebral blood flow (CBF) at the time of injection. These properties of SPECT make it particularly well-suited for epilepsy imaging, which is usually made difficult by problems with patient movement and variable seizure types. SPECT provides a "snapshot" of cerebral blood flow since scans can be acquired after seizure termination (so long as the radioactive tracer was injected at the time of the seizure). A significant limitation of SPECT is its poor resolution (about 1 cm) compared to that of MRI. Today, SPECT machines with Dual Detector Heads are commonly used, although Triple Detector Head machines are available in the marketplace. Tomographic reconstruction, (mainly used for functional "snapshots" of the brain) requires multiple projections from Detector Heads which rotate around the human skull, so some researchers have developed 6 and 11 Detector Head SPECT machines to cut imaging time and give higher resolution.
Like PET, SPECT also can be used to differentiate different kinds of disease processes which produce dementia, and it is increasingly used for this purpose. Neuro-PET has a disadvantage of requiring use of tracers with half-lives of at most 110 minutes, such as FDG. These must be made in a cyclotron, and are expensive or even unavailable if necessary transport times are prolonged more than a few half-lives. SPECT, however, is able to make use of tracers with much longer half-lives, such as technetium-99m, and as a result, is far more widely available.
Relative Advantages/Disadvantages of Imaging Types.
Magnetic Resonance Imaging (MRI) depends on magnetic activity in the brain and does not use X-rays, so it is considered more safe than imaging techniques that do use X-rays. SPECT uses gamma rays, which are characteristically more safe than other imaging systems using alpha or beta rays. Both PET and SPECT scans require the injection of radioactive materials, but the half-lives of isotopes used in SPECT can be more easily managed.
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198.Time travel.
Time travel is the concept of moving between different points in time in a manner analogous to moving between different points in space, generally using a theoretical invention known as a time machine. Time travel is a recognized concept in philosophy and fiction, but has a very limited support in theoretical physics, usually only in conjunction with quantum mechanics or Einstein?Rosen bridges.
A science fiction novel written in 1895 called The Time Machine, by H. G. Wells, was instrumental in moving the concept of time travel to the forefront of the public imagination, but the earlier short story "The Clock That Went Backward", by Edward Page Mitchell, involves a clock that, by means unspecified, allows three men to travel backward in time. Non-technological forms of time travel had appeared in a number of earlier stories such as Charles Dickens' A Christmas Carol. Historically, the concept dates back to the early mythologies of Hinduism (such as the Mahabharata). More recently, with advancing technology and a greater scientific understanding of the universe, the plausibility of time travel has been explored in greater detail by science fiction writers, philosophers, and physicists.
Forward time travel.
There is no widespread agreement as to which written work should be recognized as the earliest example of a time travel story, since a number of early works feature elements ambiguously suggestive of time travel. Ancient folk tales and myths sometimes involved something akin to traveling forward in time; for example, in Hindu mythology, the Mahabharata mentions the story of the King Raivata Kakudmi, who travels to heaven to meet the creator Brahma and is shocked to learn that many ages have passed when he returns to Earth.
The Buddhist P?li Canon also mentions time moving at different paces, and in the Payasi Sutta, one of Buddha's chief disciples Kumara Kassapa explains to the skeptic Payasi that "In the Heaven of the Thirty Three Devas, time passes at a different pace, and people live much longer. "In the period of our century; one hundred years, only a single day; twenty four hours would have passed for them."
Another of the earliest known stories to involve traveling forward in time to a distant future was the Japanese tale of "Urashima Tar?", first described in the Nihongi (720). It was about a young fisherman named Urashima Taro who visits an undersea palace and stays there for three days. After returning home to his village, he finds himself 300 years in the future, when he is long forgotten, his house in ruins, and his family long dead. Another very old example of this type of story can be found in the Talmud with the story of Honi HaM'agel who went to sleep for 70 years and woke up to a world where his grandchildren were grandparents and where all his friends and family were dead.
A more recent story involving travel to the future is Louis-Sébastien Mercier's L'An 2440, rêve s'il en fût jamais ("The Year 2440: A Dream If Ever There Were One"), a utopian novel in which the main character is transported to the year 2440. An extremely popular work (it went through 25 editions after its first appearance in 1771), it describes the adventures of an unnamed man who, after engaging in a heated discussion with a philosopher friend about the injustices of Paris, falls asleep and finds himself in a Paris of the future. Robert Darnton writes that "despite its self-proclaimed character of fantasy...L'An 2440 demanded to be read as a serious guidebook to the future."
More recently, Washington Irving's 1819 story "Rip Van Winkle" tells of a man named Rip Van Winkle who takes a nap on a mountain and wakes up 20 years in the future, when he has been forgotten, his wife dead, and his daughter grown up. Sleep was also used for time travel in Faddey Bulgarin's story "Pravdopodobnie Nebylitsi" in which the protagonist wakes up in the 29th century, and H.G. Wells' The Sleeper Awakes, about a man who wakes 200 years in the future after falling into a state of sleep resembling hibernation or suspended animation.
Backward time travel.
Backward time travel seems to be a more modern idea, but its origin is also somewhat ambiguous. One early story with hints of backward time travel is Memoirs of the Twentieth Century (1733) by Samuel Madden, which is mainly a series of letters from British ambassadors in various countries to the British Lord High Treasurer, along with a few replies from the British Foreign Office, all purportedly written in 1997 and 1998 and describing the conditions of that era. However, the framing story is that these letters were actual documents given to the narrator by his guardian angel one night in 1728; for this reason, Paul Alkon suggests in his book Origins of Futuristic Fiction that "the first time-traveler in English literature is a guardian angel who returns with state documents from 1998 to the year 1728", although the book does not explicitly show how the angel obtained these documents. Alkon later qualifies this by writing, "It would be stretching our generosity to praise Madden for being the first to show a traveler arriving from the future", but also says that Madden "deserves recognition as the first to toy with the rich idea of time-travel in the form of an artifact sent backward from the future to be discovered in the present."
Mr. and Mrs. Fezziwig dance in a vision the Ghost of Christmas Past shows Scrooge.
In 1836 Alexander Veltman published Predki Kalimerosa: Aleksandr Filippovich Makedonskii (The Forebears of Kalimeros: Alexander, son of Philip of Macedon), which has been called the first original Russian science fiction novel and the first novel to use time travel. In it, the narrator rides to ancient Greece on a hippogriff, meets Aristotle, and goes on a voyage with Alexander the Great before returning to the 19th century.
In the science fiction anthology Far Boundaries (1951), the editor August Derleth identifies the short story "Missing One's Coach: An Anachronism", written for the Dublin Literary Magazine by an anonymous author in 1838, as a very early time travel story. In this story, the narrator is waiting under a tree to be picked up by a coach which will take him out of Newcastle, when he suddenly finds himself transported back over a thousand years. He encounters the Venerable Bede in a monastery, and gives him somewhat ironic explanations of the developments of the coming centuries. However, the story never makes it clear whether these events actually occurred or were merely a dream: the narrator says that when he initially found a comfortable-looking spot in the roots of the tree, he sat down, "and as my sceptical reader will tell me, nodded and slept", but then says that he is "resolved not to admit" this explanation. A number of dreamlike elements of the story may suggest otherwise to the reader, such as the fact that none of the members of the monastery seem to be able to see him at first, and the abrupt ending in which Bede has been delayed talking to the narrator and so the other monks burst in thinking that some harm has come to him and suddenly the narrator finds himself back under the tree in the present (August 1837), with his coach having just passed his spot on the road leaving him stranded in Newcastle for another night.
Charles Dickens' 1843 book A Christmas Carol is considered by some to be one of the first depictions of time travel in both directions, as the main character, Ebenezer Scrooge, is transported to Christmases past, present and yet to come. However, these might be considered mere visions rather than actual time travel, since Scrooge only viewed each time-period passively, unable to interact with them.
A clearer example of backward time travel is found in the popular 1861 book Paris avant les hommes (Paris before Men) by the French botanist and geologist Pierre Boitard, published posthumously. In this story, the main character is transported into the prehistoric past by the magic of a "lame demon" (a French pun on Boitard's name), where he encounters such extinct animals as a Plesiosaur, as well as Boitard's imagined version of an apelike human ancestor, and is able to actively interact with some of them.
In 1881, Edward Everett Hale published "Hands Off", about an unnamed being (possibly the soul of a person who had recently died) free to travel through time and space, who interferes with Earth history in Ancient Egypt, preventing Joseph (son of Jacob) from being sold into slavery. This was the first known story to feature an alternate history being created as a result of time travel.
The first time travel story to feature time travel by means of a machine of some kind was the short story "The Clock that Went Backward" by Edward Page Mitchell, which appeared in the New York Sun in 1881. However, the mechanism is borderline fantasy in this case?a clock that, when wound, begins to run backward and transports people in the vicinity backward in time, with no explanation as to where the clock came from or how it gained this ability.
Mark Twain's A Connecticut Yankee in King Arthur's Court (1889), in which the protagonist finds himself in the time of King Arthur after a fight in which he is hit with a sledgehammer, was another early time travel story which helped bring the concept to a wide audience, and was also one of the first stories to show history being changed by a time traveler's actions.
Enrique Gaspar y Rimbau's 1887 book El Anacronópete was the first story to feature a vessel that had been engineered by an inventor to transport its riders through time. Andrew Sawyer has commented that the story "does seem to be the first literary description of a time machine noted so far", adding that "Edward Page Mitchell's story The Clock That Went Backward (1881) is usually described as the first time-machine story, but I'm not sure that a clock quite counts." This notion of a vehicle designed for time travel gained popularity with the H. G. Wells story The Time Machine, published in 1895 (preceded by a less influential story of time travel which Wells wrote in 1888, titled "The Chronic Argonauts"). The term "time machine", coined by Wells, is now universally used to refer to such a vehicle.
Since that time, both science and fiction (see Time travel in fiction) have expanded on the concept of time travel.
Some theories, most notably special and general relativity, suggest that suitable geometries of spacetime or specific types of motion in space might allow time travel into the past and future if these geometries or motions were possible. In technical papers, physicists generally avoid the commonplace language of "moving" or "traveling" through time ("movement" normally refers only to a change in spatial position as the time coordinate is varied), and instead discuss the possibility of closed timelike curves, which are worldlines that form closed loops in spacetime, allowing objects to return to their own past. There are known to be solutions to the equations of general relativity that describe spacetimes which contain closed timelike curves (such as Gödel spacetime), but the physical plausibility of these solutions is uncertain.
Relativity predicts that if one were to move away from the Earth at relativistic velocities and return, more time would have passed on Earth than for the traveler, so in this sense it is accepted that relativity allows "travel into the future" (according to relativity there is no single objective answer to how much time has really passed between the departure and the return, but there is an objective answer to how much proper time has been experienced by both the Earth and the traveler, i.e., how much each has aged; see twin paradox). On the other hand, many in the scientific community believe that backward time travel is highly unlikely. Any theory that would allow time travel would introduce potential problems of causality. The classic example of a problem involving causality is the "grandfather paradox": what if one were to go back in time and kill one's own grandfather before one's father was conceived? But some scientists believe that paradoxes can be avoided, by appealing either to the Novikov self-consistency principle or to the notion of branching parallel universes (see the 'Paradoxes' section below).
Tourism in time.
Stephen Hawking has suggested that the absence of tourists from the future is an argument against the existence of time travel: this is a variant of the Fermi paradox. Of course, this would not prove that time travel is physically impossible, since it might be that time travel is physically possible but that it is never developed (or is cautiously never used); and even if it were developed, Hawking notes elsewhere that time travel might only be possible in a region of spacetime that is warped in the correct way, and that if we cannot create such a region until the future, then time travelers would not be able to travel back before that date, so "[t]his picture would explain why" the world hasn't already been overrun by "tourists from the future." This simply means that, until a time machine were actually to be invented, we would not be able to see time travelers. Carl Sagan also once suggested the possibility that time travelers could be here, but are disguising their existence or are not recognized as time travelers, because bringing unintentional changes to the time-space continuum might bring about undesired outcomes to those travelers. It might also alter established past events. There is also the possibility that if events were changed, we would never notice it because all events following and our memories would have been instantly altered to remain congruent with the newly established timeline.
General relativity.
However, the theory of general relativity does suggest a scientific basis for the possibility of backward time travel in certain unusual scenarios, although arguments from semiclassical gravity suggest that when quantum effects are incorporated into general relativity, these loopholes may be closed. These semiclassical arguments led Hawking to formulate the chronology protection conjecture, suggesting that the fundamental laws of nature prevent time travel, but physicists cannot come to a definite judgment on the issue without a theory of quantum gravity to join quantum mechanics and general relativity into a completely unified theory.
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199.Science Fiction.
Science fiction is a genre of fiction dealing with imaginative content such as futuristic settings, futuristic science and technology, space travel, time travel, faster than light travel, parallel universes and extraterrestrial life. It often explores the potential consequences of scientific and other innovations, and has been called a "literature of ideas."
Definition.
For more details on this topic, see Definitions of science fiction.
A futuristic setting is a common but not a necessary hallmark of science fiction. A common thread in science fiction is exploring the potential consequences of scientific and other innovations on people's lives.
Science fiction is difficult to define, as it includes a wide range of subgenres and themes. Author and editor Damon Knight summed up the difficulty, saying "science fiction is what we point to when we say it", a definition echoed by author Mark C. Glassy, who argues that the definition of science fiction is like the definition of pornography: you do not know what it is, but you know it when you see it. Vladimir Nabokov argued that if we were rigorous with our definitions, Shakespeare's play The Tempest would have to be termed science fiction.
According to science fiction writer Robert A. Heinlein, "a handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the nature and significance of the scientific method." Rod Serling's definition is "fantasy is the impossible made probable. Science fiction is the improbable made possible." 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 easily delineated limits to science fiction."
Science fiction is largely based on writing rationally about alternative possible worlds or futures. It is similar to, but differs from fantasy in that, within the context of the story, its imaginary elements are largely possible within scientifically established or scientifically postulated physical laws (though some elements in a story might still be pure imaginative speculation).
The settings for science fiction are often contrary to those of consensus reality, but most science fiction relies on a considerable degree of suspension of disbelief, which is facilitated in the reader's mind by potential scientific explanations or solutions to various fictional elements. Science fiction elements include:
A time setting in the future, in alternative timelines, or in a historical past that contradicts known facts of history or the archaeological record.
A spatial setting or scenes in outer space (e.g. spaceflight), on other worlds, or on subterranean earth.
Characters that include aliens, mutants, androids, or humanoid robots and other types of characters arising from a future human evolution.
Futuristic or plausible technology such as ray guns, teleportation machines, and humanoid computers.
Scientific principles that are new or that contradict accepted physical laws, for example time travel, wormholes, or faster-than-light travel or communication.
New and different political or social systems, e.g. dystopian, post-scarcity, or post-apocalyptic.
Paranormal abilities such as mind control, telepathy, telekinesis, and teleportation.
Other universes or dimensions and travel between them.
History.
For more details on this topic, see History of science fiction.
As a means of understanding the world through speculation and storytelling, science fiction has antecedents which go back to an era when the dividing line separating the mythological from the historical tends to become somewhat blurred, though precursors to science fiction as literature can be seen in Lucian's True History in the 2nd century, some of the Arabian Nights tales, The Tale of the Bamboo Cutter in the 10th century and Ibn al-Nafis' Theologus Autodidactus in the 13th century.
A product of the budding Age of Reason and the development of modern science itself, Jonathan Swift's Gulliver's Travels (1726) was one of the first true science fantasy works, together with Voltaire's Microm?égas (1752) and Johannes Kepler's Somnium (1620?1630). Isaac Asimov and Carl Sagan considered the latter work the first science fiction story. It depicts a journey to the Moon and how the Earth's motion is seen from there. The Blazing World (1666), by English noblewoman Margaret Cavendish, has also been described as an early forerunner of science fiction. Another example is Ludvig Holberg's novel Nicolai Klimii Iter Subterraneum (1741).
Following the 18th-century development of the novel as a literary form, in the early 19th century, Mary Shelley's books Frankenstein (1818) and The Last Man helped define the form of the science fiction novel, and Brian Aldiss has argued that Frankenstein was the first work of science fiction. Later, Edgar Allan Poe wrote a story about a flight to the moon. More examples appeared throughout the 19th century.
H. G. Wells.
Then with the dawn of new technologies such as electricity, the telegraph, and new forms of powered transportation, writers including H. G. Wells and Jules Verne created a body of work that became popular across broad cross-sections of society. Wells' The War of the Worlds (1898) describes an invasion of late Victorian England by Martians using tripod fighting machines equipped with advanced weaponry. It is a seminal depiction of an alien invasion of Earth.
In the late 19th century, the term "scientific romance" was used in Britain to describe much of this fiction. This produced additional offshoots, such as the 1884 novella Flatland: A Romance of Many Dimensions by Edwin Abbott Abbott. The term would continue to be used into the early 20th century for writers such as Olaf Stapledon.
Jules Verne.
In the early 20th century, pulp magazines helped develop a new generation of mainly American SF writers, influenced by Hugo Gernsback, the founder of Amazing Stories magazine. In 1912 Edgar Rice Burroughs published A Princess of Mars, the first of his three-decade-long series of Barsoom novels, situated on Mars and featuring John Carter as the hero. The 1928 publication of Philip Nolan's original Buck Rogers story, Armageddon 2419, in Amazing Stories was a landmark event. This story led to comic strips featuring Buck Rogers (1929), Brick Bradford (1933), and Flash Gordon (1934). The comic strips and derivative movie serials greatly popularized science fiction.
In the late 1930s, John W. Campbell became editor of Astounding Science Fiction, and a critical mass of new writers emerged in New York City in a group called the Futurians, including Isaac Asimov, Damon Knight, Donald A. Wollheim, Frederik Pohl, James Blish, Judith Merril, and others. Other important writers during this period include E.E. (Doc) Smith, Robert A. Heinlein, Arthur C. Clarke, Olaf Stapledon, and A. E. van Vogt. Working outside the Campbell influence were Ray Bradbury and Stanis?aw Lem. Campbell's tenure at Astounding is considered to be the beginning of the Golden Age of science fiction, characterized by hard SF stories celebrating scientific achievement and progress. This lasted until post-war technological advances, new magazines such as Galaxy, edited by H. L. Gold, and a new generation of writers began writing stories with less emphasis on the hard sciences and more on the social sciences.
In the 1950s, the Beat generation included speculative writers such as William S. Burroughs. In the 1960s and early 1970s, writers like Frank Herbert, Samuel R. Delany, Roger Zelazny, and Harlan Ellison explored new trends, ideas, and writing styles, while a group of writers, mainly in Britain, became known as the New Wave for their embrace of a high degree of experimentation, both in form and in content, and a highbrow and self-consciously "literary" or artistic sensibility. In the 1970s, writers like Larry Niven brought new life to hard science fiction. Ursula K. Le Guin and others pioneered soft science fiction.
In the 1980s, cyberpunk authors like William Gibson turned away from the optimism and support for progress of traditional science fiction. This dystopian vision of the near future is described in the work of Philip K. Dick, such as Do Androids Dream of Electric Sheep? and We Can Remember It for You Wholesale, which resulted in the films Blade Runner and Total Recall. The Star Wars franchise helped spark a new interest in space opera, focusing more on story and character than on scientific accuracy. C. J. Cherryh's detailed explorations of alien life and complex scientific challenges influenced a generation of writers.
Emerging themes in the 1990s included environmental issues, the implications of the global Internet and the expanding information universe, questions about biotechnology and nanotechnology, as well as a post-Cold War interest in post-scarcity societies; Neal Stephenson's The Diamond Age comprehensively explores these themes. Lois McMaster Bujold's Vorkosigan novels brought the character-driven story back into prominence. The television series Star Trek: The Next Generation (1987) began a torrent of new SF shows, including three further Star Trek spin-off shows (Deep Space 9, Voyager, and Enterprise) and Babylon 5. Stargate, a movie about an ancient portal to other gates across the galaxy, was released in 1994. Stargate SG-1, a TV series, premiered on July 27, 1997 and lasted 10 seasons with 214 episodes. Spin-offs include the animated television series Stargate Infinity, the TV series Stargate Atlantis and Stargate Universe, and the direct-to-DVD films Stargate: The Ark of Truth and Stargate: Continuum. Stargate SG-1 surpassed The X-Files as the longest-running North American science fiction television series, a record later broken by Smallville.
Concern about the rapid pace of technological change crystallized around the concept of the technological singularity, popularized by Vernor Vinge's novel Marooned in Realtime and then taken up by other authors.
The term "sci-fi".
Forrest J Ackerman used the term sci-fi (analogous to the then-trendy "hi-fi") at UCLA in 1954. As science fiction entered popular culture, writers and fans active in the field came to associate the term with low-budget, low-tech "B-movies" and with low-quality pulp science fiction. By the 1970s, critics within the field such as Terry Carr and Damon Knight were using sci-fi to distinguish hack-work from serious science fiction, and around 1978, Susan Wood and others introduced the pronunciation "skiffy." Peter Nicholls writes that "SF" (or "sf") is "the preferred abbreviation within the community of sf writers and readers." David Langford's monthly fanzine Ansible includes a regular section "As Others See Us" which offers numerous examples of "sci-fi" being used in a pejorative sense by people outside the genre.
Innovation.
Science fiction has criticized developing and future technologies, but also initiates innovation and new technology. This topic has been more often discussed in literary and sociological than in scientific forums. Cinema and media theorist Vivian Sobchack examines the dialogue between science fiction films and the technological imagination. Technology impacts artists and how they portray their fictionalized subjects, but the fictional world gives back to science by broadening imagination. How William Shatner Changed the World is a documentary that gave a number of real-world examples of actualized technological imaginations. While more prevalent in the early years of science fiction with writers like Arthur C. Clarke, new authors still find ways to make currently impossible technologies seem closer to being realized.
Doctor Who is currently the longest running science fiction television series, running from 1963 to now.
Categories.
Hard SF.
Main article: Hard science fiction.
Arthur C. Clarke.
Hard science fiction, or "hard SF", is characterized by rigorous attention to accurate detail in the natural sciences, especially physics, astrophysics, and chemistry, or on accurately depicting worlds that more advanced technology may make possible. Some accurate predictions of the future come from the hard science fiction subgenre, but numerous inaccurate predictions have emerged as well. Some hard SF authors have distinguished themselves as working scientists, including Gregory Benford, Geoffrey A. Landis, David Brin, and Robert L. Forward, while mathematician authors include Rudy Rucker and Vernor Vinge. Other noteworthy hard SF authors include Isaac Asimov, Arthur C. Clarke, Hal Clement, Greg Bear, Larry Niven, Robert J. Sawyer, Stephen Baxter, Alastair Reynolds, Charles Sheffield, Ben Bova, Kim Stanley Robinson, Anne McCaffery and Greg Egan.
Soft SF.
Main article: Soft science fiction.
The description "soft" science fiction may describe works based on social sciences such as psychology, economics, political science, sociology, and anthropology. Noteworthy writers in this category include Ursula K. Le Guin and Philip K. Dick. The term can describe stories focused primarily on character and emotion; SFWA Grand Master Ray Bradbury was an acknowledged master of this art. The Eastern Bloc produced a large quantity of social science fiction, including works by Polish authors Stanislaw Lem and Janusz Zajdel, as well as Soviet authors such as the Strugatsky brothers, Kir Bulychov, Yevgeny Zamyatin and Ivan Yefremov. Some writers blur the boundary between hard and soft science fiction.
Related to social SF and soft SF are utopian and dystopian stories; George Orwell's Nineteen Eighty-Four, Aldous Huxley's Brave New World, and Margaret Atwood's The Handmaid's Tale are examples. Satirical novels with fantastic settings such as Gulliver's Travels by Jonathan Swift may also be considered science fiction or speculative fiction.
Subgenres.
Cyberpunk.
Main article: Cyberpunk.
The cyberpunk genre emerged in the early 1980s; combining cybernetics and punk, the term was coined by author Bruce Bethke for his 1980 short story Cyberpunk. The time frame is usually near-future and the settings are often dystopian in nature and characterized by misery. Common themes in cyberpunk include advances in information technology and especially the Internet, visually abstracted as cyberspace, artificial intelligence, and prosthetics and post-democratic societal control where corporations have more influence than governments. Nihilism, post-modernism, and film noir techniques are common elements, and the protagonists may be disaffected or reluctant anti-heroes. Noteworthy authors in this genre are William Gibson, Bruce Sterling, Neal Stephenson, and Pat Cadigan. James O'Ehley has called the 1982 film Blade Runner a definitive example of the cyberpunk visual style.
Time travel.
Main article: Time travel in fiction.
Time travel stories have antecedents in the 18th and 19th centuries. The first major time travel novel was Mark Twain's A Connecticut Yankee in King Arthur's Court. The most famous is H. G. Wells' 1895 novel The Time Machine, which uses a vehicle that allows an operator to travel purposefully and selectively, while Twain's time traveler is struck in the head. The term "time machine", coined by Wells, is now universally used to refer to such a vehicle. Back to the Future is one of the most popular franchises of this category. Stories of this type are complicated by logical problems such as the grandfather paradox. Time travel continues to be a popular subject in modern science fiction, in print, movies, and television episodes of Stargate SG1 and the BBC television series Doctor Who.
Alternate history.
Main article: Alternate history.
Alternative history stories are based on the premise that historical events might have turned out differently. These stories may use time travel to change the past, or may simply set a story in a universe with a different history from our own. Classics in the genre include Bring the Jubilee by Ward Moore, in which the South wins the American Civil War, and The Man in the High Castle by Philip K. Dick, in which Germany and Japan win World War II. The Sidewise Award acknowledges the best works in this subgenre; the name is taken from Murray Leinster's 1934 story Sidewise in Time. Harry Turtledove is one of the most prominent authors in the subgenre and is sometimes called the "master of alternate history."
Military SF.
Main article: Military science fiction
Military science fiction is set in the context of conflict between national, interplanetary, or interstellar armed forces; the primary viewpoint characters are usually soldiers. Stories include detail about military technology, procedure, ritual, and history; military stories may use parallels with historical conflicts. Heinlein's Starship Troopers is an early example, along with the Dorsai novels of Gordon Dickson. Joe Haldeman's The Forever War is a critique of the genre, a Vietnam-era response to the World War II?style stories of earlier authors. Prominent military SF authors include John Ringo, David Drake, David Weber, Tom Kratman, Michael Z. Williamson, S. M. Stirling, John Carr, and Don Hawthorne. The publishing company Baen Books is known for cultivating several of these military science fiction authors.
Superhuman.
Superhuman stories deal with the emergence of humans who have abilities beyond the norm. This can stem either from natural causes such as in Olaf Stapledon's novel Odd John, Theodore Sturgeon's More Than Human, and Philip Wylie's Gladiator, or be the result of scientific advances, such as the intentional augmentation in A. E. van Vogt's novel Slan. These stories usually focus on the alienation that these beings feel as well as society's reaction to them. These stories have played a role in the real life discussion of human enhancement. Frederik Pohl's Man Plus also belongs to this category.
Apocalyptic and post-apocalyptic.
Main article: Apocalyptic fiction.
Apocalyptic fiction is concerned with the end of civilization through war (On the Beach), pandemic (The Last Man), astronomic impact (When Worlds Collide), ecological disaster (The Wind from Nowhere), or some other general disaster or with a world or civilization after such a disaster. Typical of the genre are George R. Stewart's novel Earth Abides and Pat Frank's novel Alas, Babylon. Apocalyptic fiction generally concerns the disaster itself and the direct aftermath, while post-apocalyptic fiction can deal with anything from the near aftermath (as in Cormac McCarthy's The Road) to 375 years in the future (as in By The Waters of Babylon) to hundreds or thousands of years in the future, as in Russell Hoban's novel Riddley Walker and Walter M. Miller, Jr.'s A Canticle for Leibowitz. Apocalyptic science-fiction is a popular genre in video games. The critically acclaimed role-playing action adventure video game series, Fallout, is set on a post-apocalyptic Earth, where civilization is recovering from a nuclear war as survivors struggle to survive and seek to rebuild society.
Space opera.
Main article: Space opera.
Space opera is adventure science fiction set mainly or entirely in outer space or on multiple (sometimes distant) planets. The conflict is heroic, and typically on a large scale.
The term "space opera" is sometimes used pejoratively, to describe improbable plots, absurd science, and cardboard characters. But it is also used nostalgically, and modern space opera may be an attempt to recapture the sense of wonder of the golden age of science fiction. The pioneer of this subgenre is generally recognized to be Edward E. (Doc) Smith, with his Skylark and Lensman series. Gene Roddenberry's Star Trek and George Lucas's Star Wars series are among the most popular and famous franchises in cinematic space opera. It covers epic battles between good and evil throughout an entire galaxy. Alastair Reynolds's Revelation Space series, Peter F. Hamilton's Void, Night's Dawn, Pandora's Star series, Vernor Vinge's A Fire Upon the Deep, A Deepness in the Sky are newer examples of this genre. A prime example of the space opera genre seen in video games is the Mass Effect series.
Space Western.
Main article: Space Western.
Space Western transposes themes of the American Western books and film to a backdrop of futuristic space frontiers. These stories typically involve colony worlds that have only recently been terraformed and/or settled serving as stand-ins for the backdrop of lawlessness and economic expansion that were predominant in the American west. Examples include the Sean Connery film Outland, Heinlein's Farmer in the Sky, the Firefly television series, and the film sequel Serenity by Joss Whedon, as well as the manga and anime series Trigun, Outlaw Star, and Cowboy Bebop.
Social science fiction.
Main article: Social science fiction.
Social science fiction is a science fiction subgenre that focuses on themes of human society and human nature in a science fiction setting. Since it usually focuses more on the speculation of humanity and less on scientific accuracy, it's usually placed within soft science fiction.
Other subgenres.
Climate fiction or cli-fi features themes of fictional climatic settings and outcomes.
Anthropological science fiction is a subgenre that absorbs and discusses anthropology and the study of human kind. Examples include Hominids by Robert J. Sawyer, and Neanderthal by John Darnton.
Kaiju is a Japanese word that literally translates to "strange beast." The word has been translated and defined in English as "monster" and is used to refer to a genre of tokusatsu entertainment. Kaiju films feature large creatures of any form, usually attacking a major city or engaging another (or multiple) monster(s) in battle. The subgenre began in 1954 with Godzilla.
Biopunk focuses on biotechnology and subversives. The main underlying theme within these stories is the attempt to change the human body and engineer humans for specific purposes through enhancements in genetic and molecular makeups. Many examples of this subgenre include subjects such as human experimentation, the misuse of biotechnology and synthetic biotechnology. This subgenre also includes works involving human cloning and how clones might exists within human society in the future. Some consider the first biopunk novel to be Mary Shelley's Frankenstein due to the way in which Dr. Frankenstein makes his monster.
Libertarian science fiction is a subgenre focuses on the politics and social order implied by libertarian philosophies with an emphasis on individualism.
Comic science fiction is a subgenre that exploits the genre's conventions for comic effect.
Feminist science fiction poses questions about social issues such as how society constructs gender roles, the role reproduction plays in defining gender and the unequal political and personal power of men over women. Some of the most notable feminist science fiction works have illustrated these themes using utopias to explore a society in which gender differences or gender power imbalances do not exist, or dystopias to explore worlds in which gender inequalities are intensified, thus asserting a need for feminist work to continue. Joanna Russ's work, and some of Ursula K. Le Guin's work can be thus categorized. Magical feminism is a subgenre of feminist science fiction.
Steampunk is based on the idea of futuristic technology existing in the past, usually the 19th century, and often set in Victorian era England?but with prominent elements of either science fiction or fantasy, such as fictional technological inventions like those found in the works of H. G. Wells and Jules Verne, or real technological developments like the computer occurring at an earlier date. Popular examples include The Difference Engine by William Gibson and Bruce Sterling, Leviathan series by Scott Westerfeld, Bas-Lag series by China Miéville, as well as Girl Genius web comic by Phil and Kaja Foglio, although seeds of the subgenre may be seen in certain works of Michael Moorcock, Philip José Farmer and Steve Stiles, and in such games as Space: 1889 and Marcus Rowland's Forgotten Futures. Machines are most often powered by steam in this genre (hence the name). Terry Gilliam's 1985 film Brazil is seen as inspiration for writers and artists of the steampunk sub-culture.
Science fiction opera is an opera in a science fiction setting without an outer space of multi-planetary setting; therefor distinguishing it from Space opera.
Dieselpunk takes over where Steampunk leaves off. These are stories that take over as we usher in the machine-heavy eras of WWI and WWII. The use of diesel-powered machines plays heavily. In this (like its steam counterpart), the focus is on the technology.
Science-fiction poetry is poetry that has the characteristics or subject matter of science fiction. Science fiction poetry's main sources are the sciences and the literary movement of science fiction prose. An extended discussion of the field is given in Suzette Haden Elgin's The Science Fiction Poetry Handbook, where she compares and contrasts it to both mainstream poetry and to prose science fiction. The former, she maintains, uses figures of speech unencumbered by noncompliant details, whereas these details can be key elements in science-fiction poetry. Prose in science fiction has the time to develop a setting and a story, whereas a poem in the field is normally constrained by its short length to rely on some device to get a point across quickly. Elgin says that the effectiveness of this kind of poetry pivots around the correct use of presupposition. The Science Fiction Association is an international organization of speculative poets, which gives the annual Rhysling Awards for speculative poetry. An early example of science fiction in poetry is in Alfred, Lord Tennyson's Locksley Hall, where he introduces a picture of the future with "When I dipt into the future far as human eye could see...." This poem was written in 1835, near the end of the first Industrial Revolution. Poetry was only sparingly published in traditional science-fiction outlets such as pulp magazines until the New Wave. By the 1980s there were magazines specifically devoted to science-fiction poetry.
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