Thursday, 5 February 2009

The Drake Equation and Intelligent Life Elsewhere

I thought I'd have a little fun today.

A BBC News article published today claims that scientists have calculated that there could be between 361 and 38,000 intelligent civilisations in our Galaxy. This has long been a question that has interested many scientists and members of the public, but the problem was that there was so little information available. People would look at the issue; some would say that there were thousands, others that we were unique. Although rooted in science, such estimates were little more than guesswork.

Until 1995 it was not even known whether any planets existed outside our solar system. It is perhaps reasonably assumed that life cannot evolve without any such planet, called extrasolar planets. However, since then, thanks to some rather nifty astronomy, we have found 339, and a number that is increasing all the time. This makes the odds of there being intelligent life elsewhere (ILE) much greater. All of the planets found so far outsize the Earth; most are gas giants the size of Jupiter or larger. However, it is believed that if gas giants can form in a system, then smaller, rocky planets (such as Earth, Mars or Venus) are likely, if not inevitable.

So, how to work this out? When I was a teenager I was fascinated with the Drake Equation, created by Dr Frank Drake in 1960, as part of the Search for Extraterrestrial intelligence (SETI) project. It was developed to try and work out the probabilities of radio signals being sent out by ILE.

There are various forms of the equation; perhaps the most accessible is:
N = R * fp * Ne * fl * fi * fc * L

This is not as complex as it looks. Basically to work out N, (the number of races capable of communicating with us), you need to know or estimate:
  1. How many stars there are in the Galaxy at the current time (R)
  2. The number of such stars that have planets (fp)
  3. The number of those planets that can support life. In our solar system, this is one. (ne)
  4. The probability that such a planet has developed life (f)
  5. The probability that such life is intelligent (fi)
  6. The probability that the society survives long enough to send detectable signals into space (fc)
  7. The length of time that society exists (i.e. sends radio signals) (L)
As can be seen, the odds of detecting intelligent life reduces through every step; we have got firm figures for the number of stars in the Galaxy, and we now know that a good number of those stars have planets. After this, we get into total guesswork. For instance, if life develops, how likely is it for intelligent life to develop? In the 4.5 billion years that Earth has existed, only one race has developed enough intelligence to send radio waves into outer space. Is it inevitable that life, given enough time, becomes intelligent, or were we a fluke?

If you wish to try your own values, there is a Drake Equation calculator on the server. Remember, your guesses may be as accurate as any scientists...

Within my lifetime I expect many of these factors to be increasingly firmed up. Science is improving all the time. New telescopes such as the postponed Terrestrial Planet Finder from NASA or the planned Darwin mission from ESA should allow us to see exosolar planets in great detail, even to the extent of detecting chemicals required by life in atmospheric gasses. However, we are finding it hard enough to decide if there has ever been life on Mars, and that is literally in our own backyard. Any evidence found will be interpreted and argued over ad nauseum, just as the Martian meteorites have been.

In many ways this is pointless information; I cannot foresee us ever having the capability to travel to these worlds, and the knowledge that life exists on other planets will not effect the Human conciousness long term. Scientists will be excited, theologians worried, and the rest of us will continue living our lives regardless.

So what are my views? Basically, they have not changed in twenty years. I am certain there is life elsewhere amongst the 200 to 400 billion stars in our galaxy. The number is just too large, and you would have to be very, very insular to believe that Earth is unique in having developed life. Intelligent life, however, is a different matter. The fact is, after nearly fifty years of searching we have not heard anything from outer space (the Wow! signal notwithstanding). This makes me believe one of the following is probably true:
  • We are the only intelligent lifeform in the Galaxy;
  • We are not listening for messages in the right way;
  • Other ILE is too far away from us, and their signals too weak for us to detect;
  • Other ILE has developed, perhaps several times over, but died out many years ago (disease, nuclear devastation etc).
  • They are around us as we speak, watching us and waiting for the right moment to intervene...
As much as I would like for the last of these to be true, and for friendly aliens to land tomorrow outside Washington (*), I think it is highly unlikely. I like sci-fi, but I never forget the 'fi' part of the title. The distance are just so vast, even to our nearest star, Proxima Centauri, that it would be exceptionally hard to travel to it using current or realistically envisaged technology.

(*) Why is it always Washington and America that the aliens land at first? My argument would be for New Delhi or Beijing. Then again, I would love it if the aliens read the wrong map and landed outside the Old Hall in Washington, Tyne and Wear...

No comments: