[TheOtherHobbes]

There's about one particle of dust per million cubic metres. c is about 300 million metres/second. So even at 0.5c that's still a lot of particle collisions per second, each having significant kinetic energy.

Basically it would be like flying through explosive sandpaper. Each dust particle would be reduced to plasma, which creates problems of its own.

If you're accelerating there's also the Unruh Effect, which will raise the perceived temperature. By a lot.

There's no way to make this work with any kind of engineering we know about today.

[southernplaces7]

The Unruh effect is theoretical, and no evidence at all has ever been found that it's real. It literally exists as nothing more than a hypothetical mathematical model, that also happens to be debated by others who know enough to effectively debate it, and disagree.