Our universe is a dark forest,every civilization is a huntor carrying guns walks secretly in the forest like a ghost ,he softly pushes the branches aside and tries his best to avoid any sounds under his foot as well as breathing carefully.He must be catious for the reason that there are others walking like him in the forest.If he finds any life, then the only thing he will do is to shoot and kill it.In this forest,other men are hell that means they are perminent threat,any life expose themselves will be destoryed,that is the image of outer civilization,the explanation to the Fermi paradox.Scarecely had been detected,you were destoryed!