This sounds like the grey goo problem [1], but at a cosmic scale and at (near) the speed of light. Like other commenters have already said, this scenario assum

This sounds like the grey goo problem [1], but at a cosmic scale and at (near) the speed of light. Like other commenters have already said, this scenario assumes that near-speed-of-light travel is workable. [1] https://en.wikipedia.org/wiki/Gray_goo https://en.wikipedia.org/wiki/Gray_goo