The filter might also not be one in which a civilization goes extinct but one in which the civilization goes dark to any outside observers. What if the ultimate

The filter might also not be one in which a civilization goes extinct but one in which the civilization goes dark to any outside observers. What if the ultimate fate of any sufficiently sophisticated species is to harness their sun's energy to create and enter a pocket universe where the stars are still close enough together to travel between them at light speed?