Tachyonic boundary
The tachyonic boundary is the boundary where matter can no longer exist in a baryonic state and becomes tachyonic; also known as the speed of light. It is impossible to reach this boundary through conventional propulsion systems, since as the speed, or kinetic energy of baryonic matter increases, so does its mass - a baryon moving at the speed of light would have an infinite mass, and therefore require infinite energy.
Furthermore, as one approaches the tachyonic boundary, relativistic phenomenon increase exponentially in magnitude. Time relative to the moving baryon starts moving at an increasingly fast rate, while the baryon itself ages at its normal rate. This means that while a hypothetical vessel moving close to the speed of light would travel for only a month, thousands of years will pass in the Universe around it.
Of common fundamental particles, only the family of leptons, such as photons and gravitons, travel on this boundary; consisting of pure energy, they cannot possibly slow down, as is required by the symmetry of the Universe.
Beyond the tachyon boundary exists hyperspace, where all matter is tachyonic and "imaginary". To breach this barrier and reach FTL speeds, one must employ a type of Hyperspace engine with the appropriate relativistic dampeners.
