Are we searching hard enough for aliens?

It has been called the Fermi paradox, after the physicist Enrico Fermi, and it asks why - if it is so probable that life exists elsewhere in the universe - haven't we found any?The common suggestion in response to this paradox is to explain that the universe is very, very big - and there are a lot of places we could potentially find some life.Now, a trio of astrophysicists have taken another look at the "needle in a haystack" analogy and have created a model to assess how much work has actually