A big place
It would seem logical that we are not the only form of intelligent life in the Universe.
After all, the Universe is a big place. In our galaxy alone there are some estimated 400 billion stars like our own Sun. And there are billions and billions of galaxies. And scientists think that many, perhaps most, stars have planets orbiting them. Which means billions and trillions of planets.
So given the maths, it seems improbable that there could not have been some, in fact, many thousands of planets with conditions suitable for the emergence of life.
Not only that, but there’s also been plenty of time for highly intelligent life to evolve many many times over. Homo sapiens only emerged about 200 thousand years ago, and already we’ve sent men into space. Our galaxy meanwhile, is over 10 billion years old.
So the chances are that there are many intelligent forms of life out there, and that many of them have had an enormous headstart on us.
But there’s a problem with this. A chap called Enrico Fermi worked out that it wouldn’t take very long (5 to 50 million years, which, relatively speaking, is a piddling amount of time) for a civilisation with modest rocket technology to colonise our entire galaxy. Or at least, to contact every planet in the galaxy.
So the question is: where are they?
That’s Fermi’s paradox: if, as seems mathematically probable, there are many lifeforms out there, why haven’t we observed them?
It’s a bit like the objection to the possibility of time travel. While Einstein and Hawking bend our brains with talk of wormholes and the space-time continuum, a very simple question remains unanswered: “if time travel is possible, then where are all the visitors from the future?”
There have been many attempts to answer Fermi’s paradox. These include:
1) The premises of the paradox are wrong: in fact, the conditions for the emergence of life are extremely rare and unlikely, so the aliens don’t exist
2) The aliens are here but hide themselves from us
3) The aliens were here but we don’t understand their signals or we missed them
4) The universe is so big that we just haven’t come into contact with them yet
5) They do exist but there’s no motivation for contacting us or colonising the galaxy
You can find out more about this on the excellent Wikipedia site.