[A_C_Slater]

Why is it assumed that travel would have to be at the speed of light? What about 1/4 speed of light? Alpha Centauri is only about 4 light years away. So if a civilization from there could travel 1/4 speed of light they could get here in 16 years.

I know, I know the probability of an advanced civilization in the very next star system is like billions to 1, but even if it was 100 light years away that might only be 2 generations to an advancded race. Or even one generation. Or half of one. Who knows what their life spans would be.

If they can advance to 1/4 travel certainly they also have created superior biological life extending technology as well.