As the article says, this one’s food for thought for potential cosmonauts.

MIT Technology Review:

The movement of a relativistic spacecraft will have another effect. It should scatter the cosmic microwave background in a way that produces a unique signature. “As a baryonic spacecraft travels at relativistic speeds it will interact with the CMB through scattering to cause a frequency shift that could be detectable on Earth with current technology,” say Yurtsever and Wilkinson.

They go on to calculate the properties of this signature. They say the scattering should generate radiation in the terahertz to infrared regions of the spectrum and that this signal should move relative to the background. “The salient features of the signal are a rapid drop in temperature accompanied by a rapid rise in intensity, along with the motion of the source with respect to a reference frame fixed to distant quasars, which should be observable,” say Yurtsever and Wilkinson.

In other words, if relativistic spacecraft are zipping across interstellar space, this kind of signature should be visible using the current generation of astrophysical observatories.

But then there’s this:

Indeed, should some advanced civilization make this kind of jump into the cosmos, the interaction with the cosmic photons is likely to be the least of their problems since a collision with matter would be much more damaging.

It occurs to me that this would only be a problem if we’re talking about a linear traversal from point A to point B. While we’re feeding our thoughts though, we might also assume that a civilization sufficiently advanced to ford interstellar distances may have discovered how to fold space, thus obviating the need to dodge matter at all.