I'm an E.T. skeptic. The Fermi Paradox is the reason. The Fermi Paradox asks, reasonably, if intelligent life arises easily and often, then where is everybody? As old as the galaxy is, and considering the possibility of self-replicating Von Neumann probes, we shouldn't be able to swing a cat without hitting a Vulcan - or at least a robotic emissary.

The most likely answer attacks the premise of the paradox. Intelligent life (at least intelligent life that gives rise to interstellar civilizations) doesn't arise easily or often. We're alone. At least in this galaxy.

Some who have accepted this explanation of the Fermi Paradox have posited a depressing reason for E.T.'s absence - perhaps civilizations that reach our level of development tend to self-destruct.

But the great filter for interstellar civilizations doesn't have to be in front of us. There is a good argument that it is behind us.

[According to Professor Watson from the School of Environmental Sciences at the University of East Anglia] Solar models predict that the brightness of the sun is increasing, while temperature models suggest that because of this the future life span of Earth will be ‘only’ about another billion years, a short time compared to the four billion years since life first appeared on the planet.

“The Earth’s biosphere is now in its old age and this has implications for our understanding of the likelihood of complex life and intelligence arising on any given planet,” said Prof Watson.

“At present, Earth is the only example we have of a planet with life. If we learned the planet would be habitable for a set period and that we had evolved early in this period, then even with a sample of one, we’d suspect that evolution from simple to complex and intelligent life was quite likely to occur. By contrast, we now believe that we evolved late in the habitable period, and this suggests that our evolution is rather unlikely. In fact, the timing of events is consistent with it being very rare indeed.”

We're probably alone, but self destruction doesn't have to be our fate. If we can make it through the next century or so, we stand a fair chance of settling the galaxy.