Question

why existence of tachyon is not possible?​

Answer 1

Explanation:

Because a tachyon would always travel faster than light, it would not be possible to see it approaching. ... If such particles did exist, and could send signals faster than light, then according to the theory of relativity they would violate causality, leading to logical paradoxes of the "kill your own grandfather" type.

Answer 2

Explanation:

Because a tachyon would always travel faster than light, it would not be possible to see it approaching. After a tachyon has passed nearby, an observer would be able to see two images of it, appearing and departing in opposite directions.