In an article published on arXiv.org [Full article available] California-based Raytheon engineers Ulvi Yurtsever and Steven Wilkinson say that any interstellar spacecraft traveling at near-light speed would leave distinct light signatures in its wake.
While special relativity imposes an absolute speed limit at the speed of light, our Universe is not empty Minkowski spacetime. The constituents that fill the interstellar/intergalactic vacuum, including the cosmic microwave background photons, impose a lower speed limit on any object traveling at relativistic velocities. Scattering of cosmic microwave photons from an ultra-relativistic object may create radiation with a characteristic signature allowing the detection of such objects at large distances.
(Score: 2) by boristhespider on Saturday April 11 2015, @10:07PM
Google "Alcubierre solution". It might interest you.
(Practically it wouldn't work - what would happen to stars and planets, and even grains of dust and hydrogen atoms, that lay in your path? What would happen to the stars, planets, dust grains and protons that lay in your wake? Worse, the solution itself assumes that there is no gravitating matter except that which sets up the solution. General relativity is highly nonlinear, and a single hydrogen atom could disrupt the causal structures that give you a warp drive, let alone a fucking great spaceship. But even so, the concepts themselves are perfectly valid in GR.)