Tachyon
A tachyon was a subatomic particle that naturally exists at faster-than-light velocities, and can often be associated with time travel or produced as a byproduct of a temporal distortion. Tachyons exist both naturally, as in the tachyon eddies, such as those found in the Bajoran system, or can be produced artificially, such as in tachyon detection grids and temporal transponders. They can also exist as the byproducts of the use of many technologies, such as cloaking devices and transporters. (; ; )

Tachyons could be utilized in a number of ways, including as scans, offensive weapons, and even as a means of communication. (; )

Overview
Some of the 31st century temporal agent ' equipment produced tachyon radiation. In 2151, Silik detected this radiation aboard , and deduced that Daniels was on the ship, as Enterprise did not have any technology which emitted tachyons. ()

In 2366, the non-corporeal species, the Calamarain, used a tachyon field to attack Q, who had been stripped of all of his powers by the Q Continuum and deposited on board the . ()

In 2367, Captain Jean-Luc Picard instituted a tachyon detection grid on the Klingon-Romulan border, in order to prevent any cloaked Romulan ships from crossing the border undetected while cloaked. This effectively stopped the Romulan Empire's covert support for the House of Duras's attempts to take control of the Klingon Empire. Six years later, Lieutenant Tuvok suggested initiating a tachyon scan of a nebula that the  had encountered in the Delta Quadrant, in an attempt to reveal the presence of any cloaked ships which could be hiding inside. As of 2375, the Dominion began employing long-range tachyon scanners to detect cloaked vessels. They were first observed being used by the crew of the Klingon vessel Ch'Tang, after conducting a cavalry raid behind enemy lines. (; ; )

In addition, cloaked ships were known to produce detectable tachyon emissions. In 2372, the  produced a tachyon surge when decloaking in front of the , and in 2373, when a fleet of Romulan warbirds decloaked near station Deep Space 9, they produced a large buildup of tachyons. As of 2379, the Remans were able to equip the Reman Warbird Scimitar with a cloak which did not have this limitation. (; )

The Borg utilized tachyon pulses of alternating frequencies to open their transwarp conduits. In 2369,  Geordi La Forge, chief engineer of the Enterprise-D, was able to set up a temporary tachyon matrix in the ship's main deflector to simulate the pulses that the Borg used, and gain access to a transwarp conduit. Five years later, Seven of Nine attempted to utilize the same procedure to create a transwarp conduit in an effort to facilitate Voyagers return to the Alpha Quadrant, but the tachyons flooded the warp core, threatening a breach. This forced  Torres to eject the core. (; )

In an alternate timeline, Captain Picard ordered the use of an inverse tachyon pulse in three different time periods, to scan the interior of an anti-time eruption which existed in each period. It was later discovered that the tachyon pulses themselves were what ruptured the subspace barrier between time and anti-time, creating the eruption in the first place. The timeline in which these events occurred was negated when Picard was able to stop the initial formation of the eruption.' ()

In 2371, Ensign Harry Kim, operations officer aboard Voyager, attempted to utilize a tachyon scan to inspect a type 4 quantum singularity which they had encountered in the Delta Quadrant, but the attempt proved unsuccessful due to the high levels of interference produced by the singularity. ()

Later that year, temporal distortions, which existed as a result of Kes having traveled back in time from five years in the future, resulted in the presence of tachyon particles throughout Voyager. These particles caused Lieutenant Tuvok to experience a series of premonitions about the future, allowing the crew to prepare for Kes's arrival in five years time, and subsequently prevent her from traveling back in time in the first place. ()

The naturally-existing tachyon eddies in the Bajoran system helped propel ancient Bajoran lightships to warp velocities, and facilitated Bajoran arrival in the Cardassian system as early as the 16th century. Although claims of this so-called "ancient contact" were long disputed by the Cardassians, Starfleet Commander Benjamin Sisko and his son Jake finally proved it in 2371, duplicating the voyage to Cardassian space in a lightship which Sisko had constructed. ()

In 2372, Lieutenant Torres attempted to use a sustained tachyon beam to penetrate and destroy the core of the "Dreadnought," a Cardassian missile which had been transported to the Delta Quadrant. The plan failed, however, when Dreadnought, which was equipped with a sophisticated artificial intelligence system, sent a plasma burst along the tachyon beam into Voyagers main power systems. ()

In 1996, having traveled back in time from the year 2373, Tom Paris detected tachyon emissions from a truck, leading him to believe that Henry Starling, a 20th century industrialist who had stolen the 29th century timeship Aeon, was moving the vessel to another location. It was soon discovered, however, that Starling was only using a temporal transponder to divert Paris's attention. ()

Later in 2373, while trapped in an illusion created by an alien, Captain Janeway came to believe that she was being affected by a temporal anomaly, and attempted to use a tachyon burst to disperse it. ()

In 2375, When Colonel Kira was kidnapped by Dukat from Deep Space 9, a scan of her quarters revealed traces of tachyon energy, leading the crew to realize that she had been beamed away. ()

The same year, Captain Picard and Lieutenant Commander Worf were able to use a tachyon pulse to force Data, who was malfunctioning at the time, to remodulate the shield harmonics of the vessel he had stolen, so they could beam him aboard. Commander Data was later able to use the same tactic on a Son'a battle cruiser to make it possible for Worf to beam the crew to another ship. ()

In 2376, Reginald Barclay came up with the idea of using the MIDAS array to direct a tachyon beam at a class-B itinerant pulsar, creating an artificial microwormhole through which two-way communication could be established with Voyager, on the other side of the galaxy. Although his superiors were initially skeptical that the plan would work, Barclay took the initiative to implement his plan, and was able to establish communication. Two years later, Harry Kim and Seven of Nine developed a method whereby Voyager could communicate with Starfleet in the Alpha Quadrant, by bouncing a phased tachyon beam off of a quantum singularity. This method of communication was limited by the fact that the singularity was only in alignment for eleven minutes every day. ()

That same year, Voyager encountered a unique planet in the Delta Quadrant, which had a tachyon core. The core created a spacetime differential between the planet and the surrounding space, the planet experiencing the passage of one day every 1.03 seconds as measured on Voyager. Voyager became trapped in orbit briefly due to the tachyon field generated by the planet, and remained in orbit for approximately one thousand years of the planet's time. ()In the year 2404, Kathryn Janeway, who by this time had returned with Voyager to the Alpha Quadrant and been promoted to admiral, appropriated a time travel device called a "chrono deflector," invented by a Klingon scientist named Korath. The device operated by generating a powerful tachyon pulse to form a temporal rift, which could then be directed to a specific time and place. Janeway used this device to travel to the Delta Quadrant, the year 2378, where she instructed her counterpart to initiate an antitachyon pulse in order to seal the rift. Due to the fact that the chrono deflector produced levels of tachyon radiation which would be toxic to her, before she left she instructed The Doctor to treat her with chronexaline, an experimental drug at the time which protected biomatter from tachyons. Admiral Janeway subsequently collaborated with the Voyager crew to change history and return the ship to the Alpha Quadrant sixteen years before it would have without her intervention. ()

In the year 2383, the crew of the  encountered a tachyon storm. When they passed through it, it severely effected systems around the ship, including the proto-drive. This resulted in a time anomaly where the crew, while still on the same ship, were trapped and divided in their own temporal phases. The crew was also caught in oscillating time, where for some time was moving faster while moving slower for others. ()

 Appendices 
See also
 Antitachyon
 Beta-tachyon
 Long-range tachyon scanner
 Tachyokinetic energy
 Tachyon detection grid
 Tachyon eddy
 Tachyon scan
 Tachyon sweep

Apocrypha
The game Star Trek Online'' features many applications for tachyons including tachyon beams to drain a starship's shields and tachyon harmonics to disrupt personal shields in ground combat.

External link
 

cs:Tachyon
de:Tachyon
ja:タキオン
Energy
Particles
radiation
Time travel