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A tachyon (etymology; Greek: , takhus, "swift" + English: -on "elementary particle") is a hypothetical subatomic particle that travels faster than the speed of light. The first description of tachyons is attributed to German physicist Arnold Sommerfeld; however, it was George Sudarshan[citation needed], Olexa-Myron Bilaniuk,Vijay Deshpande and Gerald Feinberg(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-momentum and imaginary proper time. A tachyon is constrained to the space-like portion of the energy-momentum graph. Therefore, it cannot slow down to subluminal speeds. Even if tachyons were conventional, localizable particles, they would still preserve the basic tenets of causality in special relativity and not allow transmission of information faster than light, contrary to what has been written in many works of science fiction.