A tachyon (from the Greek polytonic|ταχυόνιον, "takhyónion", from polytonic|ταχύς, "takhýs", i.e. swift, fast) is any hypothetical particle that travels at
faster-than-light speed. The first description of tachyons is attributed to German physicist Arnold Sommerfeld; however, it was George Sudarshan, Olexa-Myron Bilaniukcite journal | author = Bilaniuk | coauthors = George Sudarshan| title = Particles beyond the Light Barrier | journal = Physics Today | month = May | year = 1969] , Vijay Deshpandecite journal | author = Bilaniuk | coauthors = Deshpande, George Sudarshan| title = Meta Relativity | journal = American Journal of Physics | year = 1962 | pages = 718ff | volume = 30 | doi = 10.1119/1.1941773 ] and Gerald Feinbergcite journal | first = Gerald | last = Feinberg | authorlink = Gerald Feinberg | title = Possibility of Faster-Than-Light Particles | journal = Physical Review | volume = 159 | year = 1967 | pages = 1089–1105 | doi = 10.1103/PhysRev.159.1089] (who originally coined the term in the 1960s) that advanced a theoretical framework for their study. Tachyonic fields have appeared theoretically in a variety of contexts, such as the Bosonic string theory. In the language of special relativity, a tachyon is a particle with space-like four-momentumand imaginary proper time. A tachyon is constrained to the space-likeportion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds.Even if tachyons were conventional, localisable particles, they would still preserve the basic tenets of causality in special relativityand not allow transmission of information faster than light, contrary to what has been written in many works of science fiction.
Today, in the framework of
quantum field theory, tachyons are best understood as signifying an instability of the system and treated using tachyon condensation, rather than as real faster-than-lightparticles, and such instabilities are described by tachyonic fields. According to the contemporary and widely accepted understanding of the concept of a particle, tachyon particles are too unstable to be treated as existing.Michael E. Peskin and Daniel V. Schroeder (1995). "An Introduction to Quantum Field Theory"Perseus books publishing.] By that theory, faster than light information transmission and causality violation with tachyons are impossible on both grounds: they are non-existent in the first place (by tachyon condensation) and even if they existed (by Feinberg's analysis) they wouldn't be able to transmit information (also by Feinberg's analysis). Despite the theoretical arguments against the existence of tachyon particles, experimental searches have been conducted to test the assumption against their existence; however, no experimental evidence for or against the existence of tachyon particles has been found."Feinberg, Gerald (1997). "Tachyon" article in "Encyclopedia Americana", Grolier Incorporated, v. 26, p.210.]
jet.Since a tachyon moves faster than the
speed of light, we can not see it approaching. After a tachyonhas passed nearby, we would be able to see two images of it, appearing and departing in opposite directions. The black line is the shock wave of Cherenkov radiation(analogous to a sonic boom), shown only in one moment of time. This double image effect is most dramatically illustrated for an observer located directly in the path of a faster-than-light object (in this example a sphere, shown in grey). The right hand bluish shape is the image formed by the blue-doppler shifted light arriving at the observer — who is located at the apex of the black Cherenkov lines — from the faster-than-light sphere as it "approaches"; it moves "backwards" as light arrives from earlier and earlier positions of the sphere before it arrived at the observer. The left-hand reddish image is formed from redshifted light that leaves the sphere "after" it passes the observer; it moves "forward" following the sphere. Since the object arrives before the light the observer sees nothing until the sphere starts to pass the observer, after which the image-as-seen-by-the-observer slowly splits into two — one of the arriving sphere (to the right) and one of the departing sphere (to the left).
] From a special relativity dynamics perspective a tachyon is a particle with
space-like four-momentum. There are two equivalent approaches to handling their kinematics:
*Requires that all the same formulas that apply to regular slower-than-light particles ("
bradyons") also apply to tachyons. In particular the energy-momentum relation::: :where p is the relativistic momentumof the bradyon and m is its rest massstill holds, along with the formula for the total energy of a particle::::which is interpreted to mean that the total energy of a particle (bradyon or tachyon) contains a contribution from the rest mass (the "rest mass-energy") and a contribution from the body's motion, the kinetic energy. :However the energy equation has, when "v" is larger than "c", an "imaginary" denominator, since the value inside the square rootis negative. Since the total energymust be real then the numerator must "also" be imaginary, i.e. the rest massm must be imaginary, since a pure imaginary number divided by another pure imaginary number is a real number.
*A simple substitution for the mass yields an equivalent way of describing tachyons with "real" masses. Define m = i*z (where ) and we get Einstein's
energy-momentum relationto read::: :With this approach the energy equation becomes::::And we avoid any necessity for imaginary masses, sidestepping the problem of interpreting exactly what a complex-valued mass may physically mean. Except, of course, when converting z back to m for interactions with non-tachyon particles
Both approaches are equivalent mathematically and have the same physical consequences. One curious effect is that, unlike ordinary particles, the speed of a tachyon "increases" as its energy decreases. (For ordinary bradyonic matter, "E" increases with increasing velocity, becoming arbitrarily large as "v" approaches "c," the
speed of light.) Therefore, just as bradyons are forbidden to break the light-speed barrier, so too are tachyons forbidden from slowing down to below "c", since to reach the barrier from either above or below requires infinite energy.
Quantizing tachyons shows that they must be spinless particles which obey
Fermi-Dirac statistics, i.e. tachyons are Scalar fermions, a combination which is not permitted for ordinary particles. They also must be created and annihilated in pairs.
The existence of such particles would pose intriguing problems in modern physics. For example, taking the formalisms of
electromagnetic radiationand supposing a tachyon had an electric charge—as there is no reason to suppose "a priori" that tachyons must be either neutral or charged—then a charged tachyon must lose energy as Cherenkov radiation—just as ordinary charged particles do when they exceed the local speed of light in a medium. A charged tachyon traveling in a vacuum therefore undergoes a constant proper timeacceleration and, by necessity, its worldlineforms a hyperbolain space-time. However, as we have seen, reducing a tachyon's energy "increases" its speed, so that the single hyperbola formed is of "two" oppositely charged tachyons with opposite momenta (same magnitude, opposite sign) which annihilate each other when they simultaneously reach infinite velocity at the same place in space. (At infinite velocity the two tachyons have no energy each and finite momentum of opposite direction, so no conservation laws are violated in their mutual annihilation. The time of annihilation is frame dependent.) Even an electrically neutral tachyon would be expected to lose energy via gravitational Cherenkov radiation, since it has a gravitational mass, and therefore increase in velocity as it travels, as described above.
Quantum field theory
The property of causality is a fundamental principle of theoretical particle physics; tachyons, if they exist, would "not" violate causality, even if they interacted with ordinary (
time-like) matter. Causality "would" be violated "if" a particle could send information into its own past, forming a so-called causal loop, leading to logical paradoxes such as the grandfather paradox. Tachyons are prevented from violating causality by the Feinberg reinterpretation principle which states that a negative-energy tachyon sent "back" in time in an attempt to violate causality can always be "reinterpreted" as a positive-energy tachyon travelling "forward" in time. This is because observers cannot distinguish between the emission and absorption of tachyons. For a tachyon, there is no distinction between the processes of emission and absorption, since there always exists a sub-light velocity reference frameshift that alters the temporal direction of the tachyon's world-line, which is not true for bradyons or photons. The attempt to "detect" a tachyon "from" the future (and violate causality) actually "creates" the same tachyon and sends it "forward" in time. (which is causal) A tachyon detector will seem to register tachyons in every possible detection model; in reality, the tachyon "detector" is spontaneously "emitting" tachyons. The effect of the reinterpretation principle on any tachyon "detector" is that any incoming tachyonic message would be lost against the tachyon background noise, which is an inevitable accompaniment of the uncontrollable emission. The counter-intuitive conclusion is that tachyons (if they existed) could be used to transmit energy-momentum, but they can't be used for communication. Thus there is no need to fall back on some quantum field theoryform of the Novikov self-consistency principleto preserve causality.
Other avenues of speculation involve parallel universes. One can imagine a scenario in which sending energy or information back in time causes history to diverge into two distinct tracks, one in which events reflect the altered information and one in which they do not.
In the theory of
general relativity, it is possible to construct spacetimes in which particles travel faster than the speed of light, relative to a distant observer. One example is the Alcubierre metric, another is of traversable wormholes. However, these are not tachyons in the above sense, as they do not exceed the speed of lightlocally.
quantum field theory, a tachyon is a quantum of a field—usually a scalar field—whose squared mass is negative, and is used to describe Spontaneous symmetry breaking: The existence of such a field implies the instability of the field vacuum; the field is at a local maximum rather than a local minimum of its potential energy, much like a ball at the top of a hill. A very small impulse (which will always happen due to quantum fluctuations) will lead the field to roll down with exponentially increasing amplitudes: it will induce tachyon condensation. It is important to realize that once the tachyonic field reaches the minimum of the potential, its quanta are not tachyons any more but rather have a positive mass-squared, such as the Higgs boson.
Technically, the squared mass is the second derivative of the
effective potential, at a point where the first derivative is zero. So for a tachyonic field the second derivative is negative, meaning that the effective potentialis at a local maximum rather than a local minimum. Therefore this situation is unstable and the field will roll down to another point, stopping only at a local minimum, where its quanta have a non-negative squared mass, so that it is not tachyonic any longer.
Since a tachyon's squared mass is negative, it formally has an imaginary mass. This is a special case of the general rule, where unstable massive particles are formally described as having a complex mass, with the real part being their mass in usual sense, and the imaginary part being the decay rate in
quantum field theory, a particle (a "one-particle state") is roughly defined as a state which is constant over time, i.e. an eigenvalueof the Hamiltonian. An unstable particle is a state which is only approximately constant over time; However, it exists long enough to be measured. This means that if it is formally described as having a complex mass, then the real part of the mass must be greater than its imaginary part. If both parts are of the same magnitude, this is considered a resonanceappearing in a scattering process rather than particle, since it does not exist long enough to be measured independently of the scattering process. In the case of a tachyon, the imaginary part of the mass is infinitely larger than the real part, and hence no concept of a particle can be attributed to it.
It is important to stress that even for
tachyonic quantum fields, the field operators at spacelike separated points still commute (or anticommute), thus preserving causality. Therefore information never moves faster than light.
Examples for tachyonic fields are all cases of
spontaneous symmetry breaking. In condensed matter physicsa notable example is Ferromagnetism; In particle physicsthe best known example is the Higgs mechanismin the standard model.
Tachyons in string theory
string theorytachyons have the same interpretation as in quantum field theory. However, string theory can, at least in principle, not only describe the physics of tachyonic fields, but also predict whether such fields appear.
Tachyonic fields indeed arise in many versions of
string theory. In general, string theory states that what we see as "particles"—electrons, photons, gravitons and so forth—are actually different vibrational states of the same underlying string. The mass of the particle can be deduced from the vibrations which the string exhibits; roughly speaking, the mass depends upon the "note" which the string sounds. Tachyons frequently appear in the spectrum of permissible string states, in the sense that some states have negative mass-squared, and therefore imaginary mass. If the tachyon appears as a vibrational mode of an open string, this signals an instability of the underlying D-branesystem to which the string is attached. The system will then decay to a state of closed strings and/or stable D-branes. If the tachyon is a closed string vibrational mode, this indicates an instability in spacetime itself. Generally, it is not known what this system will decay to. However, if the closed string tachyon is localized around a spacetime singularity the endpoint of the decay process will often have the singularity resolved.
Tachyons in fiction
Tachyons appear in many works of fiction. It has been used as a standby mechanism upon which many science fiction authors rely to establish
faster-than-lightcommunication, with or without reference to causality issues. The word "tachyon" has become widely recognized to such an extent that it can impart a science-fictional "sound" even if the subject in question has no particular relation to superluminal travel (compare " positronic brain"). Tachyons are exhibited in many novels of the late science fiction author, Frank Herbert.
Tachyons are also central in "
Gregory Benford's" seminal novel " Timescape", where the main character tries to use them in order to warn people in his past about events that are in their future (but are past for him). Part of the story is set on the Columbia Universitycampus in homage to Gerald FeinbergOld Legends, an essay by Gregory Benford, appears in New Legends, ISBN 0099319012] .
Tachyons were discussed in the NBC series "Journeyman" as an explanation of the protagonist's (Dan Vasser) ability to travel back in time.
Tachyons are extensively used in the television series "
Star Trek". In Star Trek the tachyon is used mostly in situations regarding space-time anomalies but there is no real consistency to the use of the tachyon. An "inverted tachyon" is also quite common in Star Trek. The tachyon, however, is most extensively used in the later era of Star Trek (" TNG", " VOYand " DS9").
Other places it's been used:
Doctor Who" "The Leisure Hive" - A tachyon regeneration generator was used.
Eureka" "Pilot" - A scientist causing the collision of tachyons destabilizes time and space.
Eve OnlineAn Amarrian "Named" Mega Beam Laser is the "Tachyon Beam Laser I/II" It has a slow reload time, but causes massive damage over long distance.
* Tachyons are the only known weakness of
Doctor Manhattanin the Watchmencomic book series, as his precognitive abilities can be disrupted by them. Ozymandias used this method to evade Doctor Manhattan's detection.
* Most powerful beam weapon in real-time strategy game "
The X-Files" "Synchrony" - An old man is capable of time travel through the use of tachyons.
* In the movie, "
Prince of Darkness (film)" by " John Carpenter", a tachyon beam is used to send communication of the world's impending danger from the future to characters of the movie in the form of dreams.
K-PAXby Gene Brewerreferences tachyons in Prot's explanation of time travel.
Isaac Asimov's "Foundation" novels, the oft-used "Hyperspace-Jump" is explained to be a total conversion from normal matter to tachyons, allowing for instantaneous inter-spatial travel.Fact|date=April 2008
* In the video game "
Dino Stalker", each level must be completed before time runs out. The player can collect tachyons which temporarily stop the clock for either 5 (Purple) or 30 (Blue) seconds. Tachyons can be found floating above the ground or by destroying the in game environment.
Red Dwarf" "Holoship" - Kryten says that the holoship has no mass or volume and is able to travel as super-light particles (tachyons).
* In "
Freelancer (video game)" there are weapons and shields that are "tachyon based".
* In "
Fantastic Four" "Rise of the Silver Surfer", Reed Richards suggests using a tachyon pulse to separate the Silver Surfer from his surf board.
* In "
Babylon5" tachyons are the basic particles which allow time travel, essential for the five year story arc, especially in the case of character " Jeffrey Sinclair".
* In the adventure space flight simulation computer game "" the tachyon cannon is the third most powerful blaster weapons that the player can purchase for his or her ship, behind the plasma and ionic pulse cannons.
* In Sid Meier's Alpha Centauri, the Tachyon bolt is a weapon that can be equipped to land, sea, and air combat units
Margaret Peterson Haddix's book "Found", an airplane labeled TACHYON TRAVEL appears from the future, carrying adults transformed into babies due to the time-warping effects of tachyon travel.
*In 's PS1 ending, a dying
Etherealenables a tachyon which signals the invaders seen in the next game, . This ending varies from the PC/Dos/Amiga ending those of which are considered non-canonical
Superbradyon, another class of hypothetical superluminal particles
* [http://web.archive.org/web/20001121064300/www.public.iastate.edu/~physics/sci.physics/faq/FTL.html The Faster Than Light (FTL) FAQ] (from the
* [http://scienceworld.wolfram.com/physics/Tachyon.html "Tachyon"] from
Eric Weisstein's "World of Physics"
* [http://math.ucr.edu/home/baez/physics/ParticleAndNuclear/tachyons.html Tachyon] entry from the "Physics FAQ"
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Look at other dictionaries:
tachyon — [ takjɔ̃ ] n. m. • 1970; de tachy et on des n. de particules ♦ Phys. Particule hypothétique, de vitesse supérieure à celle de la lumière dans le vide. ● tachyon nom masculin Particule hypothétique possédant une vitesse supérieure à la vitesse de… … Encyclopédie Universelle
tachyon — (n.) 1967, hypothetical faster than light particle, from TACHY (Cf. tachy ) swift + ON (Cf. on) … Etymology dictionary
tachyon — [tak′ē än΄] n. a theoretical subatomic particle conceived of as traveling faster than the speed of light: see also TARDYON … English World dictionary
Tachyon — En physique des particules, on nomme tachyon une particule (ou plutôt une classe de particules) satisfaisant aux équations de la relativité restreinte mais qui, si elle existait, se déplacerait à une vitesse supraluminique, c est à dire… … Wikipédia en Français
Tachyon — Tachyonen (von griechisch tachýs ‚schnell‘) sind hypothetische Elementarteilchen, die sich schneller als das Licht bewegen. Solche Teilchen werden als superluminar bezeichnet. Inhaltsverzeichnis 1 Tachyonen als theoretische Möglichkeit 2… … Deutsch Wikipedia
tachyon — /tak ee on /, n. Physics. a hypothetical particle that travels faster than the speed of light. [1967; TACHY + ON1] * * * Hypothetical subatomic particle whose velocity is always greater than that of light. Its existence appears consistent with… … Universalium
Tachyon — tachionas statusas T sritis fizika atitikmenys: angl. tachyon vok. Tachyon, n rus. тахеон, m; тахион, m pranc. tacheon, m; tachyon, m … Fizikos terminų žodynas
tachyon — tachionas statusas T sritis fizika atitikmenys: angl. tachyon vok. Tachyon, n rus. тахеон, m; тахион, m pranc. tacheon, m; tachyon, m … Fizikos terminų žodynas
Tachyon — Tạ|chy|on, das; s, ...yonen [engl. tachyon, zu: tachy (< griech. tachýs, ↑tachy , ↑Tachy , ) u. ↑Ion] (Kernphysik): hypothetisches Elementarteilchen, das Überlichtgeschwindigkeit besitzen soll … Universal-Lexikon
Tachyon — This hypothetical particle only travels faster than the speed of light. Data or messages could be piggy baked onto a Tachyon particle to send messages faster than light, or into the future … The writer's dictionary of science fiction, fantasy, horror and mythology