I noticed this news article today on the BBC website stating that there could be thousands of intelligent alien civilisations out there.
This is exciting stuff, and I think the confirmation of extra terrestrial intelligent life would be probably the most significant discovery in the history of our civilisation and something that I like many others, would dearly love to see in my lifetime. Despite the hope and desire for such evidence I have a little more pessimism than many of my much-respected heroes who have far greater knowledge in this area.
My simplistic view of the likelihood of alien intelligence is based on the Drake Equation. The equation takes a whole bunch of crazy variables such as the number of likely planets, the number of those in the goldilocks zone (not too hot and not too cold), and the probability of life emerging, and eventually evolving intelligence on each habitable planet before becoming extinct.
I’ve cut and pasted the full equation below from the ever reliable wikipdeia:
R* is the average rate of star formation in our galaxy
fp is the fraction of those stars that have planets
ne is the average number of planets that can potentially support life per star that has planets
fℓ is the fraction of the above that actually go on to develop life at some point
fi is the fraction of the above that actually go on to develop intelligent life
fc is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space
L is the length of time such civilizations release detectable signals into space.
Technologies in detecting extra solar planets such as Gravitational Microlensing, Transit Method and Radial Velocity have been successful in detecting over 330 planets in recent years. My understanding is that these discoveries have afforded us confidence to feed in higher values for the variables fp and ne than previous conservative estimates. I imagine that upping these values based on this new evidence has increased the value of N (the number of civilisations in our galaxy) to between 361 and 38,000 according to the BBC news article.
The reason for reserving my personal optimism is that it only takes one zero in the equation to piss on our strawberries. No matter how large the other fractions, multiplying by zero will always give you a result of zero. The variable that concerns me is fℓ. In theory it is possible for life to independently develop elsewhere, but apart from our small blue planet we have no evidence that it actually has. Even if we could see evidence of life on earth that came from another root, it would demonstrate the inevitability of life evolving eventually under the right conditions.
To me the initial spark of life could be so utterly improbable that it may have only happend once in a trillion multiverses and we only witness that one vastly improbable example through the anthropic principle. Douglas Adams, used somewhat similar logic in the quote below:
"It is known that there is an infinite number of worlds, but that not every one is inhabited. Therefore, there must be a finite number of inhabited worlds. Any finite number divided by infinity is as near to nothing as makes no odds, so if every planet in the Universe has a population of zero then the entire population of the Universe must also be zero, and any people you may actually meet from time to time are merely the products of a deranged imagination."
In order to increase my optimism in the possibility of life elsewhere the one thing I want to see is evidence of simple microbial life unconnected with our tree of life. A long extinct simple organism with nothing more than a mechanism for replication on Europa would do me. I would argue that future space missions should take this into account on deciding how to spend the meagre budget afforded by most governments for the exploration of space. Once we have found that small piece of evidence we can be confident there are no zeros in the equation and I will be convinced that it is only the vastness of space that has hindered our first contact.