How's the weather on your planet? 2

Nothing to do with bankers this time, bored with them. Just a link to a short film about the Fermi Paradox.

It's an intensely interesting subject, although I'm afraid that so many important variables are unknown at this stage that we're in the realm of speculation and guesswork. For example, in asking where everybody else in the galaxy was, Fermi assumed that there was no insurmountable problem preventing interstellar space flight in the long term. He may well have been right, but until the human race has either done it or found evidence that somebody/something else has done it, we can't be 100% sure. And I'd challenge this confident assertion from the film:

Doing some simple arithmetic from the Drake Equation gives one one star out of every 100,000,000 should have a thriving civilization.

Really? Some of the numbers we can slot into the Drake Equation are still close to being mere guesswork. To recap:

N = R* x f_p x n_e x f_ℓ x f_i x f_c x L

where:

N = the number of civilizations in our galaxy with which communication might be possible;

and

R^* = the average rate of star formation per year in our galaxy

f_p = the fraction of those stars that have planets

n_e = the average number of planets that can potentially support life per star that has planets

f_ℓ = the fraction of the above that actually go on to develop life at some point

f_i = the fraction of the above that actually go on to develop intelligent life

f_c = the fraction of civilizations that develop a technology that releases detectable signs of their existence into space

L = the length of time such civilizations release detectable signals into space

In this version of the equation, the size of N depends on seven figures. Astronomers have some data about the first two figures - the rate of star formation and the fraction of stars that have planets. They also have some information about the third figure - they know about sort of stars that probably can't support life-friendly planets and within the next few years they'll probably be able to detect a few potentially habitable planets and be able to estimate how many there might be in the galaxy, so filling in another blank.

The fraction of potentially life-bearing planets that actually go on to develop life, however, is a guess at this point. Geology suggests that our planet developed simple life almost as soon as it was cool enough for life to exist. That makes it sound as if there could be lots of life out there, but we're currently extrapolating from a sample size of one. If there's life out there, however, humans are closer to discovering it than ever before - if unicellular bugs or fossil traces of such bugs exist on Mars, Europa or Enceladus, such a discovery might be made within two or three generations. Chemical analysis of the atmospheres of extra-solar planets might confirm the presence of some form of life light years away long before humanity has the capability to carry out a detailed hunt for life in the outer Solar System.

The next number is close to being a complete guess. There's been life on earth for 3.8 billion years. Simple, single-celled microorganisms. Until about 2 billion years ago, that's all there was. Then, more complex eukaryotic cells came along. The first primitive multicellular organisms arrived 900 million years ago, evolving and diversifying ever since. If by intelligent life, we mean something at least as smart as humans, that's only just happened in geological terms - we and our cousins the chimps didn't split from our common ancestor until 6 million years ago. So far as we know, the emergence of intelligent life has only happened once on earth. This could be a one-off fluke event in our galaxy. Perhaps we're even rarer than that - after all, most of the history of life consists of single-celled bugs. Maybe multi-cellular life itself is a vanishingly rare chance event. Alternatively, intelligence might be something that's happened several times on planets which have supported evolving life for long enough. As an interested outsider, it seem to me that we're a long way from being able to say anything useful about whether our level of civilization is unique or just very rare - unless, of course an alien civilization makes itself known.

At a generous estimate, humans have been producing detectable signals of our existence for about a hundred years, a period so short as to be meaningless on a geological timescale. How long we'll continue to do it, nobody knows, how long our civilization will last nobody knows. Extrapolating from this level of ignorance to predicting one civilization per 100,000,000 stars seems pretty questionable to me. Still, it's one of the most interesting questions there is and it's fun to speculate.