[denizozger]

Michio Kaku says: "Lets say we have an ant hill in the middle of the forest. And right next to the ant hill, they’re building a ten-lane super-highway. And the question is “Would the ants be able to understand what a ten-lane super-highway is? Would the ants be able to understand the technology and the intentions of the beings building the highway next to them?"

The chance of higher civilisations being all around us, but us being too primitive to perceive them is my favourite explanation.

There is a great article about The Fermi Paradox (why we might not have been contacted - to our knowledge&proof - by extraterrestrial life): http://waitbutwhy.com/2014/05/fermi-paradox.html