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 wonkey_monkey on Saturday April 11 2015, @03:58PM
Thinking about it I guess it does just mean local matter. Throwing in the CMB confused me a bit.
systemd is Roko's Basilisk