If it is only feasible to accelerate low mass objects to the speed of light, no matter the level of technological advancement, then it might be the case that highly intelligent and technically advanced beings have reduced the mass of their own bodies to explore galaxies. Maybe the most advanced and intelligent beings are mere grams in mass. It would make for an interesting sci-fi at the very least ;-)
Or they’ve cryonically frozen their brains and put them in ships powered by nuclear explosions enabling them to travel at 0.2c assuming that the aliens at the other end of the trip will be curious enough to reanimate the brains and build them new bodies.
