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The apparent lack of anachronisms is often used as evidence against the possibility of time travel. An anachronism (from Greek ana, back, and chronos, time) is something that is out of its natural time or that appears to be so. ... Time travel is a concept that has long fascinated humanity—whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ...

"Anachronism" literally means "out of time". It can be any object or event, in fiction or in the real world, that appears out of place because it is thought to be inappropriate or impossible for that time period.

In relation to theories of time travel, the question of anachronisms has been discussed as possible disproof of (or proof for) the possibility of travelling in time. If it is possible to travel in time, why isn't there any historical evidence that people from the future have visited the past? And why are there no obvious anachronisms in our own time?

It can be assumed that if time travel is possible at any future time, that temporal explorers would travel throughout history, and the longer time travel techniques existed, the more people would travel. It might be considered inevitable that these people would leave some anachronistic evidence behind. The time travellers themselves would likely be a notable anachronism, since even something as simple as spoken language changes rapidly over time. The lack now and throughout history of any anachronistic technology, objects, or ideas could be taken as proof that time travel does not happen and therefore is not possible. "There are no anachronisms", this argument goes, "so there never will be any travellers with time machines".

Breadcrumb trails and hidden clues

The corollary of this argument is that if anachronisms exist, then this might be evidence for time travel. Some people look at history and cause and effect, and find things which appear not to have happened in a sensible chronological order, such as unbelievable accomplishments or sudden advances in technology or thought. A theorem is a statement which can be proven true within some logical framework. ...

A further theory, explored especially by science fiction and fantasy authors, suggests that time travel may be monitored for the specific purpose of controlling anachronism; the suggestion is that in the future there may be a kind of "time police" (see The End of Eternity). This group would control what people were able to do when they travelled in time, and perhaps be responsible for "correcting" errors and eddies in the space time continuum, returning history to its 'pure' path as if it had not been tampered with. This idea is strongly related to a non-deterministic or "chaos" theory of history, suggesting that any anachronistic influences would by nature be destructive, changing everything in the time line to follow. If such a body of "time police" existed, it would be hard to imagine that they would perform this task perfectly leaving no evidence behind, though one may consider that if time travel techniques were perfected, there would be infinitely many opportunities to correct a single change. The "time police" theory also presents a dramatic example of what is commonly called the grandfather paradox or the time loop paradox: if an anachronism in time was in fact corrected, how would anyone in the future know to go back and correct it? For more exploration of time paradoxes, see the time travel article. The End of Eternity by Isaac Asimov is a science fiction novel, with mystery and thriller elements, on the subjects of time travel and social engineering. ... The grandfather paradox is a paradox of time travel, supposedly first conceived by the science fiction writer René Barjavel in his book Future times three (Le voyageur imprudent, 1943). ... Time travel is a concept that has long fascinated humanity—whether it is Merlin experiencing time backwards, or religious traditions like Mohammeds trip to Jerusalem and ascent to heaven, returning before a glass knocked over had spilt its contents. ...

Both progressive and regressive anachronisms could be the result of time travel, but regressive anachronisms tend to be much stronger proof. If, say, dinosaurs are found on a remote Pacific island, that could be the result of time travel. But it could equally be that this particular island has somehow been sheltered from whatever wiped out the rest of the dinosaurs. By contrast, if Julius Caesar is caught on film in ancient Rome wearing a pair of Levis, that could only be a result of time travel (on two counts).

Other explanations

The scarcity of anachronisms may be a result of "time police", or because time travel is impossible. However, there are other possibly less dramatic explanations:

• Time travel may be very difficult. This would make anachronisms either very rare or non-existent. It might also limit time-travel to larger organisations who would be more responsible in their uses of the technology.
• The human species may become extinct shortly after the invention of time travel, so there won't be enough time [sic] to flood the past with tourists. The technology might also be developed on another planet or even by another species. Maybe time travel is itself a dangerous technology.
• It may not be possible to travel back in time past the creation of some specific artifact. The Tipler Cylinder is an example of a theoretical approach to time travel with such a limitation. In this case we'd expect to see no time travellers now, but as soon as the relevant artifact is constructed we'd expect visitors from the future to be a fact of life.

A Tipler Cylinder is a theoretical method of time travel that could conceivably work within current understanding of physics, construction of the device notwithstanding. ...

Example anachronisms

• The Great Pyramid and the Great Sphinx of Giza demonstrate impressive engineering capability, even by modern standards. Some have speculated that they may have been built by aliens, or that their construction required technology from a future civilisation. It may simply be that the masonry skills of the Ancient Egyptians were more advanced than historically thought.
• Other ancient monuments, such as Stonehenge and the statues of Easter Island, have also raised eyebrows over their feasibility, given the technology and government thought to have existed at the time.
• Leonardo da Vinci was certainly a man ahead of his time; his sketches and writings include a precursor to the modern helicopter, centuries before the invention of comparable flying machines. Leonardo's helicopter could not fly, however.
• The Antikythera mechanism, dated to around 87 BC, contains gears and clockwork technology not previously thought to exist until the 13th century.
• The Baghdad Battery has puzzled people for years.
• The Nazca Lines of Peru stretch for kilometers, and can only be observed by flying above them.
• The 1513 map of Piri Reis included a continent near South America that was taken by Charles Hapgood and Erich von Däniken as evidence for the discovery of Antarctica three centuries before its later discovery in 1820.
• The 1,600-year-old corrosion-resistant Iron pillar of Delhi.
• The Crystal Skulls required more technology for manufacturing than it is known to have been available to the Maya.
• The Aluminium wedge of Aiud, found at an archaeological site, allegedly nearby a mammoth skeleton. (Aluminium could not be produced in quantity before 1825).
• The Vitrified forts of Scotland, which are of pre-Roman origin, yet appear to have walls of melted stone which would have required immense heat.
• The Ica stones, if genuine, display scenes that are both futuristic and prehistoric.

Some people argue that these examples and others show that there have been careless time travellers and show that "temporal secret agents" have been here on containment and damage limitation missions. These are said to be the smoking guns of the ultimate conspiracy theory. The Great Pyramid of Giza (29° 58′ 45″ N 31° 08′ 01″ E) is the oldest and last remaining of the Seven Wonders of the World and the most widely recognized pyramid in the world. ... The Great Sphinx at Giza, Egypt. ... Licensure and Qualifications for the Practice of Engineering The Engineers Ring The origin of then Engineers Ring Engineering Disasters and Learning from Failure American Society of Engineering Education (ASEE) ASEE engineering profile (2003) PDF EngineersEdge GlobalSpec Categories: Architecture and engineering occupations | Engineering ... In popular fiction and conspiracy theories, life forms, especially intelligent life forms, that are of extraterrestrial origin, i. ... Masonry is the building of structures from individual units laid in and bound together by mortar. ... Map of Ancient Egypt Ancient Egypt as a general historical term broadly refers to the civilization of the Lower Nile Valley, between the First Cataract and the mouths of the Nile Delta, from circa 3300 BC until the conquest of Alexander the Great in 332 BC. As a civilization based... Stonehenge Stonehenge is a Neolithic and Bronze Age monument located near Amesbury in the English county of Wiltshire, about 8 miles (13 km) northwest of Salisbury. ... Easter Island and its location Easter Island (Polynesian: Rapa Nui (Great Rapa), Spanish: Isla de Pascua) is an island in the south Pacific Ocean belonging to Chile. ... Leonardo da Vinci Leonardo da Vinci (April 15, 1452 – May 2, 1519) was an Italian Renaissance architect, musician, anatomist, inventor, engineer, sculptor, geometer, and painter. ... A helicopter is an aircraft which is lifted and propelled by one or more large horizontal rotors (propellers). ... The Antikythera mechanism is an ancient artifact believed to be an early clockwork mechanism. ... Centuries: 2nd century BC - 1st century BC - 1st century Decades: 130s BC 120s BC 110s BC 100s BC 90s BC - 80s BC - 70s BC 60s BC 50s BC 40s BC 30s BC Years: 92 BC 91 BC 90 BC 89 BC 88 BC - 87 BC - 86 BC 85 BC 84... Spur gears found on a piece of farm equipment. ... In mechanical engineering, a clockwork is either a lightweight mechanical linkage, especially one involving multiple axles, or a complete mechanical device whose functioning relies on internal clockwork (in the preceding sense), especially where muscular effort is the sole source of operating power. ... (12th century - 13th century - 14th century - other centuries) As a means of recording the passage of time, the 13th century was that century which lasted from 1201 to 1300. ... The Baghdad Battery is the common name for a number of artifacts apparently discovered in the village of Khuyut Rabboua (near Baghdad, Iraq) in 1936. ... Satellite picture of an area containing lines. ... Events January 20 - Christian II becomes King of Denmark and Norway. ... Piri Reis (originally Hadji Muhammad) was an Ottoman admiral born around 1465, in Gallipoli on the Dardanelles. ... South America South America is a continent crossed by the equator, with most of its area in the Southern Hemisphere. ... Charles H. Hapgood, (1904-1982) was an American academician, and one of the best known advocates of a Polar shift theory. ... Erich von Däniken (born April 14, 1935 in Zofingen, Switzerland) is a controversial Swiss author who is best known for authoring works about extraterrestrial influence on human culture since prehistoric times. ... 1820 was a leap year starting on Saturday (see link for calendar). ... The iron pillar of Delhi, the capital city of India, is one of the worlds foremost metallurgical curiousities, standing in the compound of the famous Qutub Minar. ... Delhi (दिल्ली or DillÄ« in Hindi and Bengali and دیلی in Urdu) is a term that refers to either the State of Delhi or the National Capital Territory (NCT) of the Republic of India. ... A crystal skull is a model of a human skull made out of clear quartz crystal. ... The aluminium wedge of Aiud (also called the object of Aiud) is a mysterious artifact of uncertain origin in the shape of a wedge, which was found at an archeological site near the Roman town of Aiud. ... An archaeological site is a place (or group of physical sites) in which evidence of past activity is preserved (either prehistoric or historic or contemporary), and which has been investigated using the discipline of archaeology. ... Species Mammuthus columbi Columbian mammoth Mammuthus exilis Pygmy mammoth Mammuthus jeffersonii Jeffersonian mammoth Mammuthus meridionalis Mammuthus primigenius Wooly mammoth A mammoth (from Russian мамонт) is any of a number of an extinct genus of elephant, often with long curved tusks and, in northern species, a covering of long hair. ... 1825 was a common year starting on Saturday (see link for calendar). ... The Ica stones are a collection of andesite stones alleged to include ancient depictions of dinosaurs and advanced technology. ...

See also

• Ancient astronaut theory
• Paleocontact
• The End of Eternity

Ancient astronauts are conjectured extraterrestrial visitors to Earth in its distant past, whose existence was advocated by Peter Kolosimo in his 1957 book Il pianeta sconosciuto and later by the better-known Erich von Däniken in his 1968 book Chariots of the Gods and its sequels. ... Ancient astronauts are conjectured extraterrestrial visitors to Earth in its distant past, whose existence was advocated by Peter Kolosimo in his 1957 book Il pianeta sconosciuto and later by the better-known Erich von Däniken in his 1968 book Chariots of the Gods and its sequels. ... The End of Eternity by Isaac Asimov is a science fiction novel, with mystery and thriller elements, on the subjects of time travel and social engineering. ...

History

• 2002-3: Published by Wikimedia, Edited by Wikipedia contributors, Entitled Anachronism and time travel
• 2002: Published by h2g2, Written by a girl called Ben, Entitled Hellmans' Anachronism: an hypothesis about historical proof of future time travel