About aliens , here is a theory , maybe there is 1 species of aliens that developed for millions of years to become the apex predator and it has so far exterminated all other species that developed past a certain point of space travel. If you think about it, it really only takes 1 alien species, if its advanced enough and can instantly travel anywhere and detect space travel across the universe and so on. <br><br>the other theory is that everytime a species develops to a certain point it destroys itself by the sheer power required to travel to other stars. <br><br>I am more leaning towards the 1 aggressive super alien species that exterminates everything else.