Why have humans never found aliens?

“IF ALIENS are so likely, why have we never seen any?” That is the Fermi Paradox—named after Enrico Fermi, a physicist who posed it in 1950.

Fermi’s argument ran as follows. The laws of nature supported the emergence of intelligent life on Earth. Those laws are the same throughout the universe. The universe contains zillions of stars and planets. So, even if life is unlikely to arise on any particular astronomical body, the sheer abundance of creation suggests the night sky should be full of alien civilisations. Fermi wondered why aliens had never visited Earth. Today, the paradox is more usually cast in light of the inability of radio-telescope searches to detect the equivalent of the radio waves that leak from Earth into the cosmos, and have done for the past century.