Is there anybody out there?

Enrico Fermi, one of the fathers of atomic power, wrote: “If the estimates of the large numbers of other civilizations in the Galaxy or Universe are correct, given that some of them must have evolved millions of years before us, why have we never been visited or even contacted?”

It’s good question, and precision cosmology may provide the answer. The current estimate of the number of galaxies in the ‘known’ universe is at least 100,000,000,000. These contain, between them, approximately, 100,000,000,000,000,000,000,000 stars…

When considering the possibility of extraterrestrial life, the debate usually starts with uncertainty as the extent of other planets in the Universe. But now that around 2,000 exoplanets have been discovered, it seems likely that most stars will have some; if our solar system is typical, and each star has three or four rocky planets orbiting it, the ‘observable universe’ could contain around 400,000,000,000,000,000,000,000 planets…

If we accept that life spontaneously evolved from complex organic molecules on Earth 3,600,000,000 years ago, it seems remotely unlikely that over a period of 13,000,000,000 years (since the Big Bang), and with so many planets to choose from, life has not appeared elsewhere…

But if, as Fermi suggested, intelligent life has existed even millions of years before us, why, with so many stars to choose from should anyone bother coming to look for us? Very simple: no-one knows we’re here… Of all manifestations of ‘intelligent’ life on Earth, only radio signals can be detected from the stars. It is only since the 1930s when TV broadcasting began using UHF frequencies, that signals have penetrated the ionosphere and leaked into space. In the 80 years or so since then, radio signals have barely penetrated 80 light years into the Galaxy which is 100,000 light years across… No more than a few hundred stars out of the 100,000,000,000 in the Galaxy could have detected our transmissions and even that would assume that they had massive radio telescopes pointed in our direction.

The truth is, we’re completely isolated. The Galaxy is vast but the Universe is immense. There are probably millions of civilizations out there, but no-one knows we’re here…