Worm hole

In physics, a wormhole is a hypothetical topologicalfeature of spacetime that is, fundamentally, a 'shortcut' through space and time. Simply,spacetime is a two-dimensional (2-D) surface that, when 'folded' over, allows the formation of a wormhole bridge. A wormhole has at least two mouths that are connected via a throat or tube. If the wormhole is traversable, then matter can 'travel' from one mouth to the other via the throat. There is no observational evidence for wormholes, and, although wormholes are valid solutions in general relativity, this is only true if exotic matter can be used to stabilize them. Even if the wormhole is stabilized, even a slight fluctuation in space would collapse it. If such exotic matter — that is, matter with negative mass — does not exist, all wormhole-containing solutions to Einstein’s field equations are vacuum solutions, which require an impossible vacuum, free of all matter and energy.

The American theoretical physicist John Archibald Wheeler coined the term wormhole in 1957; however, in 1921, the German mathematicianHermann Weyl already had proposed the wormhole theory, in connection with mass analysis ofelectromagnetic field energy.^[1]

This analysis forces one to consider situations . . . where there is a net flux of lines of force, through what topologists would call ‘a handle’ of the multiply-connected space, and what physicists might perhaps be excused for more vividly terming a ‘wormhole’.

—John Wheeler in Annals of Physics

Contents [hide] 1 Definition 2 Schwarzschild wormholes 3 Traversability 3.1 Faster-than-light travel 3.2 Time travel 4 Metrics 5 In fiction 6 See also 7 Notes 8 References 9 External links

[edit]Definition

The basic notion of an intra-universe wormhole is that it is a compact region of spacetime whose boundary is topologically trivial but whose interior is not simply connected. Formalizing this idea leads to definitions such as the following, taken from Matt Visser's Lorentzian Wormholes.

If a Minkowski spacetime contains a compact region Ω, and if the topology of Ω is of the form Ω ~ R x Σ, where Σ is a three-manifold of the nontrivial topology, whose boundary has topology of the form dΣ ~ S², and if, furthermore, the hypersurfaces Σ are all spacelike, then the region Ω contains a quasipermanent intra-universe wormhole.

Characterizing inter-universe wormholes is more difficult. For example, one can imagine a 'baby' universe connected to its 'parent' by a narrow 'umbilicus'. One might like to regard the umbilicus as the throat of a wormhole, but the spacetime is simply connected.

[edit]Schwarzschild wormholes

Embedded diagram of a Schwarzschild wormhole.

Lorentzian wormholes known as Schwarzschild wormholes or Einstein-Rosen bridges are bridges between areas of space that can be modeled asvacuum solutions to the Einstein field equations by combining models of a black hole and a white hole. This solution was discovered by Albert Einstein and his colleague Nathan Rosen, who first published the result in 1935. However, in 1962 John A. Wheeler and Robert W. Fuller published a paper showing that this type of wormhole is unstable, and that it will pinch off instantly as soon as it forms, preventing even light from making it through.

Before the stability problems of Schwarzschild wormholes were apparent, it was proposed that quasars were white holes forming the ends of wormholes of this type.

While Schwarzschild wormholes are not traversable, their existence inspired Kip Thorne to imagine traversable wormholes created by holding the 'throat' of a Schwarzschild wormhole open with exotic matter (material that has negative mass/energy).

[edit]Traversability

Lorentzian traversable wormholes would allow travel from one part of the universe to another part of that same universe very quickly or would allow travel from one universe to another. The possibility of traversable wormholes in general relativity was first demonstrated by Kip Thorne and his graduate student Mike Morris in a 1988 paper; for this reason, the type of traversable wormhole they proposed, held open by a spherical shell of exotic matter, is referred to as a Morris-Thorne wormhole. Later, other types of traversable wormholes were discovered as allowable solutions to the equations of general relativity, including a variety analyzed in a 1989 paper by Matt Visser, in which a path through the wormhole can be made in which the traversing path does not pass through a region of exotic matter. However in the pure Gauss-Bonnet theory exotic matter is not needed in order for wormholes to exist- they can exist even with no matter.^[2] A type held open by negative mass cosmic strings was put forth by Visser in collaboration with Cramer et al.,^[3] in which it was proposed that such wormholes could have been naturally created in the early universe.

Wormholes connect two points in spacetime, which means that they would in principle allow travel in time, as well as in space. In 1988, Morris, Thorne and Yurtsever worked out explicitly how to convert a wormhole traversing space into one traversing time.^[4] However, it has been said a time traversing wormhole cannot take a person back to before it was made^{[citation needed]} but this is disputed^{[by whom?]}.

[edit]Faster-than-light travel

Special relativity only applies locally. Wormholes allow superluminal (faster-than-light) travel by ensuring that the speed of light is not exceeded locally at any time. While traveling through a wormhole, subluminal (slower-than-light) speeds are used. If two points are connected by a wormhole, the time taken to traverse it would be less than the time it would take a light beam to make the journey if it took a path through the space outside the wormhole. However, a light beam traveling through the wormhole would always beat the traveler. As an analogy, running around to the opposite side of a mountain at maximum speed may take longer than walking through a tunnel crossing it. A person can walk slowly while reaching his or her destination more quickly because the distance is smaller.

[edit]Time travel

A wormhole could allow time travel.^[4] This could be accomplished by accelerating one end of the wormhole to a high velocity relative to the other, and then sometime later bringing it back; relativistic time dilation would result in the accelerated wormhole mouth aging less than the stationary one as seen by an external observer, similar to what is seen in the twin paradox. However, time connects differently through the wormhole than outside it, so that synchronized clocks at each mouth will remain synchronized to someone traveling through the wormhole itself, no matter how the mouths move around. This means that anything which entered the accelerated wormhole mouth would exit the stationary one at a point in time prior to its entry.

For example, consider two clocks at both mouths both showing the date as 2000. After being taken on a trip at relativistic velocities, the accelerated mouth is brought back to the same region as the stationary mouth with the accelerated mouth's clock reading 2005 while the stationary mouth's clock read 2010. A traveller who entered the accelerated mouth at this moment would exit the stationary mouth when its clock also read 2005, in the same region but now five years in the past. Such a configuration of wormholes would allow for a particle's world line to form a closed loop in spacetime, known as aclosed timelike curve.

It is thought that it may not be possible to convert a wormhole into a time machine in this manner; some analyses using the semiclassical approach to incorporating quantum effects into general relativity indicate that a feedback loop of virtual particles would circulate through the wormhole with ever-increasing intensity, destroying it before any information could be passed through it, in keeping with the chronology protection conjecture. This has been called into question by the suggestion that radiation would disperse after traveling through the wormhole, therefore preventing infinite accumulation. The debate on this matter is described by Kip S. Thorne in the book Black Holes and Time Warps. There is also theRoman ring, which is a configuration of more than one wormhole. This ring seems to allow a closed time loop with stable wormholes when analyzed using semiclassical gravity, although without a full theory of quantum gravity it is uncertain whether the semiclassical approach is reliable in this case.

[edit]Metrics

Unidentified flying objec

commonly abbreviated as UFO or U.F.O.) is the popular term for any aerial phenomenon whose cause cannot be easily or immediately identified by the observer. The United States Air Force, which coined the term in 1952, initially defined UFOs as those objects that remain unidentified after scrutiny by expert investigators,^[1] though the term UFO is often used more generally to describe any sighting unidentifiable to the reporting observer(s). Popular culture frequently takes the term UFO as a synonym for alien spacecraft. Cults have become associated with UFOs, and mythology and folklore have evolved around the phenomenon.^[2] Some investigators now prefer to use the broader term unidentified aerial phenomenon (or UAP), to avoid the confusion and speculative associations that have become attached toUFO.^[3] Another widely known acronym for UFO in Spanish, French, Portuguese and Italian is OVNI.

Studies have established that the majority of UFOs are observations of some real but conventional object—most commonly aircraft, balloons, or astronomical objects such as meteors or bright planets—that have been misidentified by the observer as anomalies while a small percentage of reported UFOs are hoaxes.^[4] Only a small percentage of reported sightings (usually 5 to 20%) can be classified as unidentified flying objects in the strictest sense (see below for some studies).

Some scientists have argued that all UFO sightings are misidentifications of natural phenomena^[5] and historically, there was debate among some scientists about whether scientific investigation was warranted given available empirical data.^{[6][7][8][9][10]} Very little peer-reviewed literature has been published in which scientists have proposed, studied or supported non-prosaic explanations for UFOs. Nevertheless, over the years UFOs have been the subject of many investigations that have varied widely in scope and scientific rigor.

UFO reports became frequent after the first widely publicized U.S. sighting, reported by private pilot Kenneth Arnold in 1947, that gave rise to the popular terms "flying saucer" and "flying disc." Since then, millions of people have reported that they have seen UFOs.^[11]

Contents [hide] 1 History 1.1 The Kenneth Arnold sightings 2 Investigations 2.1 American investigations 3 Famous American cases 3.1 Canadian investigation 4 Famous Canadian cases 4.1 French investigation 4.2 British investigation 5 Famous British cases 5.1 Uruguayan investigation 5.2 Astronomer reports 5.3 British records on UFOs 6 Identification of UFOs 6.1 UFO hypotheses 7 Physical evidence 7.1 Reverse engineering 8 Ufology 8.1 UFO researchers 8.2 UFO organizations 8.3 UFO categorization 8.4 UFO skeptics 9 Conspiracy theories 9.1 Allegations of evidence suppression 10 Famous hoaxes 11 UFOs in popular culture 11.1 Use in film and television 12 See also 13 References 13.1 General 13.2 Skepticism 13.3 Psychology 13.4 Histories 13.5 Technology 13.6 Notes 14 External links

History

Unexplained aerial observations have been reported throughout history. Some were undoubtedly astronomical in nature: comets, bright meteors, one or more of the five planets that can be seen with the naked eye, planetary conjunctions, or atmospheric optical phenomena such asparhelia and lenticular clouds. An example is Halley's Comet, which was recorded first by Chinese astronomers in 240 B.C. and possibly as early as 467 B.C.

Other historical reports seem to defy prosaic explanation, but assessing such accounts is difficult. Whatever their actual cause, such sightings throughout history were often treated as supernatural portents, angels, or other religious omens. Some objects in medieval paintings can seem strikingly similar to UFO reports.^[12] Art historians explain those objects as religious symbols, often represented in many other paintings of Middle-Age and Renaissance.^[13]

Shen Kuo (1031–1095), a Song Chinese government scholar-official and prolific polymath inventor and scholar, wrote a vivid passage in hisDream Pool Essays (1088) about an unidentified flying object. He recorded the testimony of eyewitnesses in 11th-century Anhui and Jiangsu(especially in the city of Yangzhou), who stated that a flying object with opening doors would shine a blinding light from its interior (from an object shaped like a pearl) that would cast shadows from trees for ten miles in radius, and was able to take off at tremendous speeds.^[14]

• On January 25, 1878, The Denison Daily News wrote that local farmer John Martin had reported seeing a large, dark, circular flying object resembling a balloon flying "at wonderful speed." Martin also said it appeared to be about the size of a saucer, the first known use of the word "saucer" in association with a UFO.^[15]
• On February 28, 1904, there was a sighting by three crew members on the USS Supply 300 miles west of San Francisco, reported by Lt. Frank Schofield, later to become Commander-in-Chief of the Pacific Battle Fleet. Schofield wrote of three bright red egg-shaped and circular objects flying in echelon formation that approached beneath the cloud layer, then changed course and "soared" above the clouds, departing directly away from the earth after two to three minutes. The largest had an apparent size of about six suns.^[16]
• 1916 and 1926: The three oldest known pilot UFO sightings, of 1305 cataloged by NARCAP. On January 31, 1916, a UK pilot nearRochford reported a row of lights, like lighted windows on a railway carriage, that rose and disappeared. In January 1926, a pilot reported six "flying manhole covers" between Wichita, Kansas and Colorado Springs, Colorado. In late September 1926, an airmail pilot over Nevada was forced to land by a huge, wingless cylindrical object.^[17]
• On August 5, 1926, while traveling in the Humboldt Mountains of Tibet's Kokonor region, Nicholas Roerich reported that members of his expedition saw "something big and shiny reflecting the sun, like a huge oval moving at great speed. Crossing our camp the thing changed in its direction from south to southwest. And we saw how it disappeared in the intense blue sky. We even had time to take our field glasses and saw quite distinctly an oval form with shiny surface, one side of which was brilliant from the sun.” ^[18] Another description by Roerich was, "...A shiny body flying from north to south. Field glasses are at hand. It is a huge body. One side glows in the sun. It is oval in shape. Then it somehow turns in another direction and disappears in the southwest." ^[19]
• In the Pacific and European theatres during World War II, "Foo-fighters" (metallic spheres, balls of light and other shapes that followed aircraft) were reported and on occasion photographed by Allied and Axis pilots. Some proposed Allied explanations at the time included St. Elmo's Fire, the planet Venus, hallucinations from oxygen deprivation, or German secret weapon.^[20][21]
• On February 25, 1942, U.S. Army observers reported unidentified aircraft both visually and on radar over the Los Angeles, California region. Antiaircraft artillery was fired at what was presumed to be Japanese planes. No readily apparent explanation was offered, though some officials dismissed the reports of aircraft as being triggered by anxieties over expected Japanese air attacks on California. However, Army Chief of Staff Gen. George C. Marshall and Secretary of War Henry Stimson insisted real aircraft were involved. The incident later became known as the Battle of Los Angeles, or the West coast air raid.
• In 1946, there were over 2000 reports, collected primarily by the Swedish military, of unidentified aerial objects in the Scandinavian nations, along with isolated reports from France, Portugal, Italy and Greece, then referred to as "Russian hail", and later as "ghost rockets", because it was thought that these mysterious objects were possibly Russian tests of captured German V1 or V2 rockets. Although most were thought to be natural phenomena like meteors, over 200 were tracked on radar and deemed to be "real physical objects" by the Swedish military. In a 1948 top secret document, the Swedish military told the USAF Europe in 1948 that some of their investigators believed them to be extraterrestrial in origin. (See Wiki ghost rockets article for details)

The Kenneth Arnold sightings

Main article: Kenneth Arnold#June 24, 1947 UFO sighting

This shows the report Kenneth Arnold filed in 1947 about his UFO sighting.

The post World War II UFO phase in the United States began with a famous sighting by American businessman Kenneth Arnold on June 24, 1947 while flying his private plane near Mount Rainier,Washington. He reported seeing nine brilliantly bright objects flying across the face of Rainier.

This shows Kenneth Arnoldholding a picture of a drawing of the crescent shaped UFO he saw in 1947.

Although there were other 1947 U.S. sightings of similar objects that preceded this, it was Arnold's sighting that first received significant media attention and captured the public's imagination. Arnold described what he saw as being "flat like a pie pan", "shaped like saucers and were so thin I could barely see them… ", "half-moon shaped, oval in front and convex in the rear. … they looked like a big flat disk" (see Arnold's drawing at right), and flew "like a saucer would if you skipped it across the water". (One of the objects, however, he would describe later as crescent-shaped, as shown in illustration at left.) Arnold’s descriptions were widely reported and within a few days gave rise to the terms flying saucer and flying disk.^[22] Arnold’s sighting was followed in the next few weeks by hundreds of other reported sightings, mostly in the U.S., but in other countries as well.

After reports of the Arnold sighting hit the media, other cases began to be reported in increasing numbers. In one instance a United Airlines crew sighting of nine more disc-like objects over Idaho on the evening of July 4. At the time, this sighting was even more widely reported than Arnold’s and lent considerable credence to Arnold’s report.^[23]

American UFO researcher Ted Bloecher, in his comprehensive review of newspaper reports (including cases that preceded Arnold's), found a sudden surge upwards in sightings on July 4, peaking on July 6–8. Bloecher noted that for the next few days most American newspapers were filled with front-page stories of the new "flying saucers" or "flying discs". Reports began to rapidly tail off after July 8,^[24] when officials began issuing press statements on the Roswell UFO incident, in which they explained debris found on the ground by a rancher as being that of a weather balloon.^[25]

Over several years in the 1960s, Bloecher (aided by physicist James E. McDonald) discovered 853 flying disc sightings that year from 140 newspapers from Canada, Washington D.C, and every U.S. state except Montana.^[26]

Investigations

UFOs have been subject to investigations over the years that vary widely in scope and scientific rigor. Governments or independent academics in the United States, Canada, the United Kingdom, Japan, Peru, France, Belgium, Sweden, Brazil, Chile, Uruguay, Mexico, Spain, and the Soviet Union are known to have investigated UFO reports at various times.

Among the best known government studies are the ghost rockets investigation by the Swedish military (1946–1947), Project Blue Book, previously Project Sign and Project Grudge, conducted by the United States Air Force from 1947 until 1969, the secret U.S. Army/Air Force Project Twinkle investigation into green fireballs (1948–1951), the secret USAF Project Blue Book Special Report #14 ^[27] by the Battelle Memorial Institute, and Brazilian Air Force Operation Saucer (1977). France has had on ongoing investigation (GEPAN/SEPRA/GEIPAN) within its space agency CNES since 1977, as has Uruguay since 1989.

A public research effort conducted by the Condon Committee for the USAF, which arrived at a negative conclusion in 1968, marked the end of the US government's official investigation of UFOs, though documents indicate various government intelligence agencies continue unofficially to investigate or monitor the situation.^[28]

Allen Hynek was a trained astronomer who participated in Project Bluebook after doing research as a federal government employee. He formed the opinion that some UFO reports could not be scientifically explained. Through his founding of the Center for UFO Studies and participation at CUFOs he spent the rest of his life researching and documenting UFOs. The movie Close Encounters of the Third Kind had a character loosely based on Hynek. Another group studying UFOs is Mutual UFO Network. MUFON is a grass roots based organization known for publishing one of the first UFO investigators handbooks. This handbook went into great detail on how to document alleged UFO sightings.

Jacques Vallée, a scientist and prominent UFO researcher, has argued that most UFO research is scientifically deficient, including many government studies such as Project Blue Book, and that mythology and cultism are frequently associated with the phenomenon. Vallée states that self-styled scientists often fill the vacuum left by the lack of attention paid to the UFO phenomenon by official science, but also notes that several hundred professional scientists continue to study UFOs in private, what he terms the "invisible college". He also argues that much could be learned from rigorous scientific study, but that little such work has been done.^[2]

There has been little mainstream scientific study of UFOs, and the topic has received little serious attention or support in mainstream scientific literature. Official studies ended in the U.S. in December 1969, subsequent to the statement by Edward Condon that the study of UFOs probably could not be justified in the expectation that science would be advanced.^[8] The Condon report and these conclusions were endorsed by the National Academy of Scientists, of which Condon was a member. However, a scientific review by the UFO subcommittee of the AIAAdisagreed with Condon's conclusion, noting that at least 30% of the cases studied remained unexplained, and that scientific benefit might be gained by continued study.

It has been claimed that all UFO cases are anecdotal^[29] and that all can be explained as prosaic natural phenomena. On the other hand, it has been argued that there is limited awareness among scientists of observational data, other than what is reported in the popular press.^[2][30]

Controversy has surrounded the Condon report, both before and after it was released. It has been claimed that the report was "harshly criticized by numerous scientists, particularly at the powerful AIAA … [who] recommended moderate, but continuous scientific work on UFOs".^[8]. In an address made to the AAAS, James E. McDonald stated that he believed science had failed to mount adequate studies of the problem, criticizing the Condon report and prior studies by the US Air Force for being scientifically deficient. He also questioned the basis for Condon's conclusions^[31] and argued that the reports of UFOs have been "laughed out of scientific court."^[7] J. Allen Hynek, an astronomer whose position as USAF consultant from 1948 made him perhaps the most knowledgeable scientist connected with the subject, sharply criticized the report of the Condon Committee and later wrote two nontechnical books that set forth the case for investigating seemingly baffling UFO reports.

No official government investigation has ever publicly concluded that UFOs are indisputably real, physical objects, extraterrestrial in origin, or of concern to national defense. These same negative conclusions also have been found in studies that were highly classified for many years, such as the UK's Flying Saucer Working Party, Project Condign, the US CIA-sponsored Robertson Panel, the US military investigation into the green fireballs from 1948 to 1951, and the Battelle Memorial Institute study for the USAF from 1952 to 1955 (Project Blue Book Special Report #14).

However, the initially classified USAF Regulation 200-2, first issued in 1953 after the Robertson Panel, which first defined UFOs and how information was to be collected, stated explicitly that the two reasons for studying the unexplained cases were for national security reasons and for possible technical aspects involved, implying physical reality and concern about national defense, but without opinion as to origins. (For example, such information would also be considered important if UFOs had a foreign or domestic origin.) The first two known classified USAF studies in 1947 also concluded real physical aircraft were involved, but gave no opinion as to origins. (See American investigations immediately below) These early studies led to the creation of the USAF's Project Sign at the end of 1947, the first semi-public USAF study.

Project Sign in 1948 wrote a highly classified opinion (see Estimate of the Situation) that the best UFO reports probably had an extraterrestrial explanation, as did the private but high-level French COMETA study of 1999. A top secret Swedish military opinion given to the USAF in 1948 stated that some of their analysts believed the 1946 ghost rockets and later flying saucers had extraterrestrial origins. (see Ghost rockets for document). In 1954, German rocket scientist Hermann Oberth revealed an internal West German government investigation, which he headed, that arrived at an extraterrestrial conclusion, but this study was never made public. Classified, internal reports by the Canadian Project Magnetin 1952 and 1953 also assigned high probability to extraterrestrial origins. Publicly, however, Project Magnet, nor later Canadian defense studies, ever stated such a conclusion.

Another highly classified U.S. study was conducted by the CIA's Office of Scientific Investigation (OS/I) in the latter half of 1952 after being directed to do so by the National Security Council (NSC). They concluded UFOs were real physical objects of potential threat to national security. One OS/I memo to the CIA Director (DCI) in December read, "...the reports of incidents convince us that there is something going on that must have immediate attention... Sightings of unexplained objects at great altitudes and traveling at high speeds in the vicinity of major U.S. defense installations are of such a nature that they are not attributable to natural phenomena or any known types of aerial vehicles." The matter was considered so urgent, that OS/I drafted a memorandum from the DCI to the NSC proposing that the NSC establish an investigation of UFOs as a priority project throughout the intelligence and the defense research and development community. They also urged the DCI to establish an external research project of top-level scientists to study the problem of UFOs, now known as the Robertson Panel, to further analyze the matter. The OS/I investigation was called off after the Robertson Panel's negative conclusions in January 1953.^[32]

Some public government conclusions have indicated physical reality but stopped short of concluding extraterrestrial origins, though not dismissing the possibility. Examples are the Belgian military investigation into large triangles over their airspace in 1989–1991 and the recent 2009 Uruguay Air Force study conclusion (see below).

Some private studies have been neutral in their conclusions, but argued the inexplicable core cases called for continued scientific study. Examples are the Sturrock Panel study of 1998 and the 1970 AIAA review of the Condon Report.

American investigations

Following the large U.S. surge in sightings in June and early July 1947, on July 9, 1947, Army Air Force (AAF) intelligence, in cooperation with the FBI, began a formal investigation into selected best sightings with characteristics that could not be immediately rationalized, which includedKenneth Arnold’s and that of the United Airlines crew. The AAF used "all of its scientists" to determine whether or not "such a phenomenon could, in fact, occur". The research was "being conducted with the thought that the flying objects might be a celestial phenomenon," or that "they might be a foreign body mechanically devised and controlled."^[33] Three weeks later in a preliminary defense estimate, the air force investigation decided that, "This ‘flying saucer’ situation is not all imaginary or seeing too much in some natural phenomenon. Something is really flying around."^[34]

A further review by the intelligence and technical divisions of the Air Materiel Command at Wright Field reached the same conclusion, that "the phenomenon is something real and not visionary or fictitious," that there were objects in the shape of a disc, metallic in appearance, and as big as man-made aircraft. They were characterized by "extreme rates of climb [and] maneuverability," general lack of noise, absence of trail, occasional formation flying, and "evasive" behavior "when sighted or contacted by friendly aircraft and radar," suggesting a controlled craft. It was thus recommended in late September 1947 that an official Air Force investigation be set up to investigate the phenomenon. It was also recommended that other government agencies should assist in the investigation.^[35]

This led to the creation of the Air Force’s Project Sign at the end of 1947, one of the earliest government studies to come to a secret extraterrestrial conclusion. In August 1948, Sign investigators wrote a top-secret intelligence estimate to that effect. The Air Force Chief of StaffHoyt Vandenberg ordered it destroyed. The existence of this suppressed report was revealed by several insiders who had read it, such as astronomer and USAF consultant J. Allen Hynek and Capt. Edward J. Ruppelt, the first head of the USAF's Project Blue Book.^[36]

Project Sign was dismantled and became Project Grudge at the end of 1948. Angered by the low quality of investigations by Grudge, the Air Force Director of Intelligence reorganized it as Project Blue Book in late 1951, placing Ruppelt in charge. Blue Book closed down in 1970, using the Condon Commission's negative conclusion as a rationale, ending the official Air Force UFO investigations. However, a 1969 USAF document, known as the Bolender memo, plus later government documents revealed that nonpublic U.S. government UFO investigations continued after 1970. The Bollender memo first stated that "reports of unidentified flying objects that could affect national security… are not part of the Blue Book system," indicating that more serious UFO incidents were already handled outside of the public Blue Book investigation. The memo then added, "reports of UFOs which could affect national security would continue to be handled through the standard Air Force procedures designed for this purpose." ^[37] In addition, in the late 1960s, there was a chapter on UFOs at the U.S. Air Force Academy in their Space Sciences course, giving serious consideration to possible extraterrestrial origins. When word of the curriculum became public, the Air Force in 1970 put out a statement the book was outdated and that cadets were now being informed of Condon's negative conclusion instead.^[38]

Use of UFO instead of the popular flying saucer was first suggested in 1952 by Ruppelt, who felt that flying saucer did not reflect the diversity of the sightings. Ruppelt suggested that UFO should be pronounced as a word — you-foe. However it is generally pronounced by forming each letter: U.F.O. His term was quickly adopted by the Air Force, which also briefly used "UFOB" circa 1954, for Unidentified Flying Object. Ruppelt recounted his experiences with Project Blue Book in his memoir, The Report on Unidentified Flying Objects (1956), also the first book to use the term.^[39]

Air Force Regulation 200-2,^[40] issued in 1953 and 1954, defined an Unidentified Flying Object ("UFOB") as "any airborne object which by performance, aerodynamic characteristics, or unusual features, does not conform to any presently known aircraft or missile type, or which cannot be positively identified as a familiar object." The regulation also said UFOBs were to be investigated as a "possible threat to the security of the United States" and "to determine technical aspects involved." As to what the public was to be told, "it is permissible to inform news media representatives on UFOB's when the object is positively identified as a familiar object," but "For those objects which are not explainable, only the fact that ATIC [Air Technical Intelligence Center] will analyze the data is worthy of release, due to many unknowns involved." ^[41][42]

Well known American investigations include:

• Project Blue Book, previously Project Sign and Project Grudge, conducted by the United States Air Force from 1947 until 1969
• The secret U.S. Army/Air Force Project Twinkle investigation into green fireballs (1948–1951)
• Ghost rockets investigations by the Swedish, U.K., U.S., and Greek militaries (1946–1947)
• The secret CIA Office of Scientific Investigation (OS/I) study (1952–53)
• The secret CIA Robertson Panel (1953)
• The secret USAF Project Blue Book Special Report No. 14 by the Battelle Memorial Institute (1951–1954)
• The Brookings Report (1960), commissioned by NASA
• The public Condon Committee (1966–1968)
• The private, internal RAND Corporation study (1968)^[43]
• The private Sturrock Panel (1998)

Another early U.S. Army study, established sometime in the 1940s and of which little is known, was called the Interplanetary Phenomenon Unit(IPU). In 1987, British UFO researcher Timothy Good received a letter confirming the existence of the IPU from the Army Director of Counter-intelligence, in which it was stated, "… the aforementioned Army unit was disestablished during the late 1950s and never reactivated. All records pertaining to this unit were surrendered to the U.S. Air Force Office of Special Investigations in conjunction with operation BLUEBOOK." The IPU records have never been released.^[44]

Thousands of documents released under FOIA also indicate that many U.S. intelligence agencies collected (and still collect) information on UFOs, including the Defense Intelligence Agency (DIA), FBI, CIA, National Security Agency (NSA), as well as military intelligence agencies of the Army and Navy, in addition to the Air Force.^[45]

The investigation of UFOs has also attracted many civilians, who in the U.S formed research groups such as National Investigations Committee On Aerial Phenomena (NICAP, active 1956–1980), Aerial Phenomena Research Organization (APRO, 1952–1988), Mutual UFO Network(MUFON, 1969–), and Center for UFO Studies (CUFOS, 1973–).

Famous American cases

The Battle of Los Angeles in 1942, where an unidentified flying object erroneously was thought to be part of a Japanese airstrike.

The Roswell Incident involved New Mexico residents, local law enforcement officers, and the US military, the latter of whom allegedly collected physical evidence from the UFO crash site.

In the Kecksburg Incident, Pennsylvania residents reported seeing a bell shaped object crash in the area. Peace officers, and possibly military personnel, were sent to investigate.

The Betty and Barney Hill abduction was the first reported abduction incident.

Canadian investigation

The Falcon Lake incidentreport filed by the Royal Canadian Mounted Police on Stephen Michalak claimed incident with a UFO.

In Canada, the Department of National Defence has dealt with reports, sightings and investigations of UFOs across Canada. In addition to conducting investigations into crop circles in Duhamel, Alberta, it still considers "unsolved" the Falcon Lake incident in Manitoba and the Shag Harbour incident in Nova Scotia.^[46]

Early Canadian studies included Project Magnet (1950–1954) and Project Second Story (1952–1954), supported by the Defence Research Board. These studies were headed by Canadian Department of Transport radio engineer Wilbert B. Smith, who later publicly supported extraterrestrial origins.

Famous Canadian cases

In the Shag Harbour incident, an alleged UFO was seen in the water. Numerous people were involved, including the Royal Canadian Mounted Police and local residents. Nothing was ever found. Around the same time, both the Canadian and US military were involved in another UFO-related search at Shelburne, Nova Scotia, approximately 30 miles from Shag Harbour.

French investigation

Wikinews has related news: French Space Agency CNES releases UFO files Pilots spot 'UFOs' near the Channel Islands

On March 2007, the French Centre National d'Études Spatiales(CNES) published an archive of UFO sightings and other phenomena online.^[47]

French studies include GEPAN/SEPRA/GEIPAN (1977–), within the French space agency CNES, the longest ongoing government-sponsored investigation. About 14% of some 6000 cases studied remained unexplained. The official opinion of GEPAN/SEPRA/GEIPAN has been neutral or negative, but the three heads of the studies have gone on record in stating that UFOs were real physical flying machines beyond our knowledge or that the best explanation for the most inexplicable cases was an extraterrestrial one.^[48]

The French COMETA panel (1996–1999) was a private study undertaken mostly by aerospace scientists and engineers affiliated with CNES and high-level French Air Force military intelligence analysts, with ultimate distribution of their study intended for high government officials. The COMETA panel likewise concluded the best explanation for the inexplicable cases was the extraterrestrial hypothesis and went further in accusing the United States government of a massive cover-up.^[49]

British investigation

The UK conducted various investigations into UFO sightings and related stories. The contents of some of these investigations have since been released to the public.

Eight file collections on UFO sightings, dating from 1978 to 1987, were first released on May 14, 2008, to the UK National Archives by theMinistry of Defence.^[50] Although kept secret from the public for many years, most of the files have low levels of classification and none is classified Top Secret. 200 files are set to be made public by 2012. The files are correspondence from the public sent to government officials, such as the MoD and Margaret Thatcher. The MoD released the files under the Freedom of Information Act due to requests from researchers.^[51] These files include, but are not limited to, UFOs over Liverpool and the Waterloo Bridge in London.^[52]

On October 20, 2008 more UFO files were released. One case released detailed that in 1991 an Alitalia passenger aircraft was approachingHeathrow Airport when the pilots saw what they described as a "cruise missile" flew extremely close to the cockpit. The pilots believed that a collision was imminent. UFO expert David Clarke says that this is one of the most convincing cases for a UFO he has come across.^[53]

British investigations include the UK's Flying Saucer Working Party. Its final report, published in 1951, remained secret for over 50 years. The Working Party concluded that all UFO sightings could be explained as misidentifications of ordinary objects or phenomena, optical illusions, psychological delusions or hoaxes. The report stated: ‘We accordingly recommend very strongly that no further investigation of reported mysterious aerial phenomena be undertaken, unless and until some material evidence becomes available’.

A secret study of UFOs undertaken for the UK’s Ministry of Defence (MoD) between 1996 and 2000 and was publicly released in 2006. The report is titled "Unidentified Aerial Phenomena in the UK Defence Region" and was code-named Project Condign. The report confirmed earlier findings that the main causes of UFO sightings are misidentification of man-made and natural objects. The report noted: "No artefacts of unknown or unexplained origin have been reported or handed to the UK authorities, despite thousands of UAP reports. There are no SIGINT,ELINT or radiation measurements and little useful video or still IMINT." It concluded: "There is no evidence that any UAP, seen in the UKADR [UK Air Defence Region], are incursions by air-objects of any intelligent (extraterrestrial or foreign) origin, or that they represent any hostile intent."

In contrast, Nick Pope, who headed the MoD UFO desk from 1991 to 1994, states that while about 80 % of the cases he investigated were misidentifications of known objects and phenomena (while 15 % of sightings had insufficient information), about 5 % "seemed to defy any conventional explanation." These included cases with multiple and/or highly trained witnesses such as pilots or military personnel, corroboration from radar or video/photography, and involved apparent structured craft with speeds and maneuverability beyond that of human origin.^[54]Stopping short of an extraterrestrial explanation (though not discounting it), Pope believes the UFO phenomenon is quite real and raises serious defense, national security, and air safety issues. Pope describes many of the perplexing cases, such as the Rendlesham Forest incident, and the politics surrounding UFOs in his book Open Skies, Closed Minds.

Famous British cases

Both US and British military personnel allegedly witnessed UFOs in the forests near Rendlesham Rendlesham Forest incident and Bentwaters. This case was reported in December 1980 and took place over several nights at both the US and RAF military bases.

Uruguayan investigation

The Uruguayan Air Force has had an ongoing UFO investigations since 1989 and analyzed 2100 cases, of which they consider only 40 (about 2%) definitely lacking any conventional explanation. All files have recently been declassified. The unexplained cases include military jet interceptions, abductions, cattle mutilations, and physical landing trace evidence. Colonel Ariel Sanchez, who currently heads the investigation, summarized their findings as follows: "The commission managed to determine modifications to the chemical composition of the soil where landings are reported. The phenomenon exists. It could be a phenomenon that occurs in the lower sectors of the atmosphere, the landing of aircraft from a foreign air force, up to the extraterrestrial hypothesis. It could be a monitoring probe from outer space, much in the same way that we send probes to explore distant worlds. The UFO phenomenon exists in the country. I must stress that the Air Force does not dismiss an extraterrestrial hypothesis based on our scientific analysis."^[55]

Astronomer reports

The Air Force's Project Blue Book files indicate that approximately 1 %^[56] of all unknown reports came from amateur and professional astronomers or other users of telescopes (such as missile trackers or surveyors). In 1952, astronomer J. Allen Hynek, then a consultant to Blue Book, conducted a small survey of 45 fellow professional astronomers. Five reported UFO sightings (about 11%). In the 1970s, astrophysicist Peter A. Sturrock conducted two large surveys of the American Institute of Aeronautics and Astronautics and American Astronomical Society. About 5 % of the members polled indicated that they had had UFO sightings.

Astronomer Clyde Tombaugh, who admitted to six UFO sightings, including three green fireballs, supported the Extraterrestrial hypothesis (ETH) for UFOs and stated he thought scientists who dismissed it without study were being "unscientific." Another astronomer was Lincoln LaPaz, who had headed the Air Force's investigation into the green fireballs and other UFO phenomena in New Mexico. LaPaz reported two personal sightings, one of a green fireball, the other of an anomalous disc-like object. (Both Tombaugh and LaPaz were part of Hynek's 1952 survey.) Hynek himself took two photos through the window of a commercial airliner of a disc-like object that seemed to pace his aircraft.^[57]Even later UFO debunker Donald Menzel filed a UFO report in 1949.

In 1980, a survey of 1800 members of various amateur astronomer associations by Gert Helb and Hynek for the Center for UFO Studies(CUFOS) found that 24 % responded "yes" to the question "Have you ever observed an object which resisted your most exhaustive efforts at identification?"^[58]

British records on UFOs

In August 2009 The Black Vault internet archive announced the release by the British government of more than 4,000 pages of declassified records.^[59] The records include information on the Rendlesham Forest incident, crop circles, a UFO attack on a cemetery and even reports ofalien abduction claims ^[60].

On 1st December 2009, the British Ministry of Defense (MoD) quietly closed down its UFO investigations unit. The unit's hotline and email address were suspended by the Ministry of Defense on that date. The MoD said there was no value in continuing to receive and investigate sightings in a release, stating

"... in over fifty years, no UFO report has revealed any evidence of a potential threat to the United Kingdom. The MoD has no specific capability for identifying the nature of such sightings. There is no Defence benefit in such investigation and it would be an inappropriate use of defence resources. Furthermore, responding to reported UFO sightings diverts MoD resources from tasks that are relevant to Defence."

The Guardian reported that the MoD claimed the closure would save the Ministry around 50,000 pounds a year. The MoD said that it would continue to release UFO files to the public through the National Archives ^[61].

Identification of UFOs

Main article: Identification studies of UFOs

Fata Morgana, a type of mirage in which objects located below the astronomical horizon appear to be hovering in the sky, may be responsible for some UFO sightings. Fata Morgana can also magnify the appearance of distant objects or distort them to be unrecognizable.^[62]

Studies show that after careful investigation, the majority of UFOs can be identified as ordinary objects or phenomena (see Identification studies of UFOs). The most commonly found identified sources of UFO reports are:

• Astronomical objects (bright stars, planets, meteors, re-entering man-made spacecraft, artificial satellites, and the moon)
• Aircraft (Aerial advertising and other aircraft, missile launches)
• Balloons (weather balloons, prank balloons, large research balloons)

Much less common sources of UFO reports include:

• Other atmospheric objects and phenomena (birds, unusual clouds, kites, flares)
• Light phenomena (mirages, Fata Morgana, moon dogs, searchlights and other ground lights, etc.)
• Hoaxes

A 1952–1955 study by the Battelle Memorial Institute for the US Air Force included these categories as well as a "psychological" one. However, the scientific analysts were unable to come up with prosaic explanations for 21.5 % of the 3200 cases they examined and 33 % of what were considered the best cases remained unexplained, double the number of the worst cases. (See full statistical breakdown inIdentification studies of UFOs). Of the 69 % identifieds, 38 % were deemed definitely explained while 31 % were thought to be "questionable." About 9 % of the cases were considered to have insufficient information to make a determination.

The official French government UFO investigation (GEPAN/SEPRA/GEIPAN), run within the French space agency CNES between 1977 and 2004, scientifically investigated about 6000 cases and found that 13.5 % defied any rational explanation, 46 % were deemed definitely or likely identifiable, while 41 % lacked sufficient information for classification.

An individual 1979 study by CUFOS researcher Allan Hendry found, as did other investigations, that only a small percentage of cases he investigated were hoaxes (<1 id="cite_ref-62" class="reference" style="line-height: 1em; font-weight: normal; font-style: normal; ">[63] However, Hendry's figure for unidentified cases was considerably lower than many other UFO studies such as Project Blue Book or the Condon Report that have found rates of unidentified cases ranging from 6 % to 30 %. Hendry found that 88.6 % of the cases he studied had a clear prosaic explanation, and he discarded a further 2.8 % due to unreliable or contradictory witnesses or insufficient information. The remaining 8.6 % of reports could not definitively be explained by prosaic phenomena, although he felt that a further 7.1 % could possibly be explained, leaving only the very best 1.5 % without plausible explanation.

UFO hypotheses

The inclusion or exclusion of items from this list, or length of this list, is disputed. Please discuss this issue on the talk page.

To account for unsolved UFO cases, several hypotheses have been proposed.

• The Extraterrestrial hypothesis (ETH), defined by Edward U. Condon in the 1968 Condon Report as "The idea that some UFOs may be spacecraft sent to Earth from another civilization, or on a planet associated with a more distant star", further attributing the popularity of the idea to Donald Keyhoe's UFO book from 1950,^[64] though the idea clearly predated Keyhoe, appearing in newspapers and various government documents (see immediately below). This is probably the most popular theory among Ufologists. Some private or governmental studies, some secret, have concluded in favor of the Extraterrestrial hypothesis (ETH), or have had members who disagreed with official conclusions against the conclusion by committees and agencies to which they belonged.^{[65][66][67][68][69][70][71][72]}
• The Interdimensional hypothesis, that UFOs are objects crossing over from other dimensions or parallel universe, popularly proposed byJacques Vallée,^[73] though also predating him.
• The paranormal/occult hypothesis; A variant of the Interdimensional Hypothesis, invoked to explain so-called paranormal aspects sometimes associated with UFO reports
• The psychosocial hypothesis, that what people report as UFO experiences is the result of psychological misperception mechanisms and is strongly influenced by popular culture.
• That UFOs represent poorly understood or still unknown natural phenomena, such as ball lightning or sprites.^[74]
• The Earthquake lights/Tectonic Strain hypothesis: UFOs are caused by strains in Earth's crust near earthquake faults, which can also supposedly induce hallucinations.
• That UFOs are military flying saucers; top secret or experimental aircraft unfamiliar to most people.^[75]

Physical evidence

Besides visual sightings, reports sometimes include claims of indirect and direct physical evidence, including cases studied by the military and various government agencies of different countries (such as Project Blue Book, the Condon Committee, the French GEPAN/SEPRA, and Uruguay's current Air Force study).

Reported physical evidence cases have also been studied by various private scientist and engineers. For example, researcher Ted Phillips, a protege of J. Allen Hynek at CUFOS, has studied 3200 so-called UFO trace evidence cases typically associated with alleged landings or close interactions. Such traces include such things as tree and foliage damage, vehicle damage, electromagnetic effects, radiation, various residues, footprints, and soil depression, burning, and desiccation.^[76] Although many such cases have dubious provenance, a number have been well-studied and authenticated by government studies, such as the 1964 Lonnie Zamora Socorro, N.M. case, the 1967 Canadian Falcon Lake Incident, and the 1981 French Trans-en-Provence Case. Phillips has compiled a list of some of the best-quality authenticated cases.^[77]

A comprehensive scientific review of physical evidence cases was carried out by the 1998 Sturrock UFO panel, with specific examples of many of the categories listed below.^[78]

• Radar contact and tracking, sometimes from multiple sites. These may involve trained military personnel and control tower operators, simultaneous visual sightings, and aircraft intercepts. One such recent example were the mass sightings of large, silent, low-flying black triangles in 1989 and 1990 over Belgium, tracked by multiple NATO radar and jet interceptors, and investigated by Belgium's military (included photographic evidence).^[79] Another famous case from 1986 was the JAL 1628 case over Alaska investigated by the FAA.^[80]
• Photographic evidence, including still photos, movie film, and video.^[81]
• Claims of physical trace of landing UFOs, including ground impressions, burned and/or desiccated soil, burned and broken foliage, magnetic anomalies^[specify], increased radiation levels, and metallic traces. See, e. g. Height 611 UFO Incident or the 1964 Lonnie Zamora's Socorro,New Mexico encounter of the USAF Project Blue Book cases). A well-known example from December 1980 was the USAF Rendlesham Forest Incident in England. Another less than two weeks later, in January 1981, occurred in Trans-en-Provence and was investigated byGEPAN, then France's official government UFO-investigation agency. Project Blue Book head Edward J. Ruppelt described a classic 1952 CE2 case involving a patch of charred grass roots.^[82]
• Physiological effects on people and animals including temporary paralysis, skin burns and rashes, corneal burns, and symptoms superficially resembling radiation poisoning, such as the Cash-Landrum incident in 1980. One such case dates back to 1886, a Venezuelan incident reported in Scientific American magazine.^[83]
• Animal/cattle mutilation cases, that some feel are also part of the UFO phenomenon.^[84]
• Biological effects on plants such as increased or decreased growth, germination effects on seeds, and blown-out stem nodes (usually associated with physical trace cases or crop circles)^[85]
• Electromagnetic interference (EM) effects. A famous 1976 military case over Tehran, recorded in CIA and DIA classified documents, resulted in communication losses in multiple aircraft and weapons system failure in an F-4 Phantom II jet interceptor as it was about to fire a missile on one of the UFOs. This was also a radar/visual case.^[86]
• Remote radiation detection, some noted in FBI and CIA documents occurring over government nuclear installations at Los Alamos National Laboratory and Oak Ridge National Laboratory in 1950, also reported by Project Blue Book director Ed Ruppelt in his book.^[87]
• Actual hard physical evidence cases, such as 1957, Ubatuba, Brazil, magnesium fragments analyzed by the Brazilian government and in the Condon Report and by others. The 1964 Socorro/Lonnie Zamora incident also left metal traces, analyzed by NASA.^[88] A more recent example involves "the Bob White object" a tear drop shaped object recovered by Bob White and was featured in the TV show UFO hunters^[89]
• Angel hair and angel grass, possibly explained in some cases as nests from ballooning spiders or chaff.^[90]

Reverse engineering

Attempts have been made to reverse engineer the possible physics behind UFOs through analysis of both eyewitness reports and the physical evidence, on the assumption that they are powered vehicles. Examples are former NASA and nuclear engineer James McCampbell in his bookUfology,^[91] NACA/NASA engineer Paul R. Hill in his book Unconventional Flying Objects, and German rocketry pioneer Hermann Oberth^[92]. Among subjects tackled by McCampbell, Hill, and Oberth was the question of how UFOs can fly at supersonic speeds without creating a sonic boom. McCampbell's proposed solution is microwave plasma parting the air in front of the craft. In contrast, Hill and Oberth believed UFOs utilize an as yet unknown anti-gravity field to accomplish the same thing as well as provide propulsion and protection of occupants from the effects of high acceleration.^[93]