Tachyons.

Tachyons as opposed to tardyons. Tardyons are ordinary particles. Tachy is greek for speed, If I am not wrong. Well these particles are supposed to go faster than the speed of light, Imaginary rest mass.
If they exist there will be a universal clock with a single reference. Think about it.
Still they have never been sighted till now.
Theoritically particles which move faster than light emit a kinda radiation and if this is isolated in the incoming cosmic rays. It is a good enough proof. But everything has turned blank.
This tachyon is real cool meaning As its velocity increases its energy decreases. Some say this is basis for time travel. I dont buy that.
According to some this particle does not violate Special Theory of relativity. What they do is that assign imaginary rest mass. Also that whenever tachyons occur they will have to be faster than the speed of light. These particles come under the group superluminal particle.
Some thing else like tachyons known as Bradyons also exist these are supposed to have greater energy than the tachyon.