anyone know what a tackion is?

A tachyon (from the Greek ταχύς takhús, meaning "swift") is any hypothetical particle that travels at superluminal velocity. The first description of tachyons is attributed to German physicist Arnold Sommerfeld, but it was George Sudarshan and Gerald Feinberg (who originally coined the term) in the 1960s who advanced a theoretical framework for their study. Tachyons have recurred in a variety of contexts, such as string theory, and in science fiction. In the language of special relativity, a tachyon is a particle with space-like four-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it can never slow to light speed or below.

You can look it up on wikipedia, but i'll tell you the answer and the website it's on.

As mentioned above, a tachyon is a particle with space-like four-momentum. If its energy and momentum are real, its rest mass is imaginary. One curious effect is that, unlike ordinary particles, the speed of a tachyon increases as its energy decreases. This is a consequence of special relativity because the tachyon, in theory, has a negative squared mass. According to Einstein, the total energy of a particle contains a contribution from the rest mass (the "rest mass-energy") and a contribution from the body's motion, the kinetic energy. If m denotes the rest mass, then the total energy is given by the relation

E = \frac{mc^2}{\sqrt{1 - \frac{v^2}{c^2}}}.

We take this relation to be valid for either tachyons or regular particles ("tardyons"). For ordinary matter, this equation shows that E increases with increasing velocity, becoming arbitrarily large as v approaches c, the speed of light. If m is imaginary, on the other hand, the denominator of the fraction must also be imaginary to keep the energy a real number (since a pure imaginary divided by another pure imaginary is real). The denominator will be imaginary if the quantity inside the square root is negative, which only happens if v is larger than c. Therefore, just as tardyons are forbidden to break the light-speed barrier, so too are tachyons forbidden from slowing down to below light speed.

The existence of such particles would pose intriguing problems in modern physics. For example, taking the formalisms of electromagnetic radiation and 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 an accelerating tachyon must radiate electromagnetic waves, just like ordinary charged particles do. However, as we have seen, reducing a tachyon's energy increases its speed, and so in this regime a small acceleration would produce a larger one, leading to a run-away effect similar to an ultraviolet catastrophe.

Some modern presentations of tachyon theory have demonstrated the possibility of a tachyon with a real mass. In 1973, Philip Crough and Roger Clay reported a superluminal particle apparently produced in a cosmic ray shower (an observation which has not been confirmed or repeated) [1]. This possibility has prompted some to propose that each particle in space has its own relative timeline, allowing particles to travel back in time without violating causality. Under this model, such a particle would be a "tachyon" by virtue of its apparent superluminal velocity, even though its rest mass is a real number.

Link: http://en.wikipedia.org/wiki/Tachyon

And there's me thinking it was something made up for star trek! But waita minute, if a tackyon is ANY theoretical particle travelling at superluminal speeds, hen when they use a tackyon beam on Star Trek, it is technically theoretical?! Or have they found a tackyon beam and are to lazy to name it something else, after all, there could be multiple particles that fast so therefore tackyon is a 'group' name!

Clever i am!

All I know is that you can spot a cloaked Romulan Warbird using a tachyon field. From other answers, it looks like it's a bonifide theoretical particle, but I've only heard it mentioned science fiction.

Supposedly a tachyon is a particle or wave form which travels faster than the speed of light but there is no proof that they exist.

Tachyon - a theoretical particle that must move faster than light, transcending Einstein's limit.

A Tachyon is a hypothetical particle that travels at superluminal velocity.

It does not have tomato sauce on it....

A theoretical particle that travels faster then light

super natural velocity