The Davey Dialogues - An Exploration of the Scientific Foundations of Human Culture. John C. Madden
by astronomers as they observe our universe.
The formula itself is simply the product of a set of fractions and average numbers multiplied by the rate of star formation in our galaxy; the equation addresses the likelihood of communication with intelligent life elsewhere in our galaxy only. If we wanted a likelihood for the whole universe, we might choose to multiply our result by the number of galaxies in the universe reduced by a factor that reflects the considerable difficulty of communication over distances greater than the diameter of our galaxy. If we sent a message to an intelligent being one million light years away, it would be at least two million years before we could receive a reply. And if we wanted to compute the likelihood of communication with intelligent life outside our universe, well, we probably would have to ask you, Davey, for an estimate!
Davey responded immediately.
– I’ve already given you an answer! Not today!
– That’s disappointing. Perhaps you have a headache?
I paused to emphasize my displeasure, then I continued.
– Drake’s formula looks like this:
N (the number of civilizations in our galaxy with which we might be able to communicate at any given time) equals:
R (the rate of star formation in our galaxy (about 6 per year), times
fp (the fraction of those stars that have planets [current estimates are 20–50 per cent]), times
ne (the average number of planets per star with planets that can potentially support life – a figure between 1 and 5 has been suggested), times
fl (the fraction of planets in ne where life actually evolves – fractions ranging from 0 all the way to 1 have been suggested), times
fi (the fraction of fl where intelligent life evolves – some believe that the fraction should be close to 1, because the survival advantage of intelligence is very large, hence intelligence is almost certain to develop; others see the development of brains in life forms as being highly improbable, perhaps as small as 1 chance in 10 million), times
fc (the fraction of intelligent life (fi ), which develops both the means and the desire to communicate externally – most guesses are in the 10–20 per cent range), times
L (the average expected duration of the intelligent and communicating life forms calculated above – now there is a challenging number to estimate! We have only our own experience to go on. Some pessimists have estimated an average duration as low as 68 years. Drake himself suggested 10,000 years. Perhaps he was an optimist, but humankind in our present form appears to have been around for about 160,000 years, of which we have been attempting to communicate with extraterrestrial beings for only 50 or 60 years. The pessimistic estimate has us almost overdue for disappearance! Even the optimistic suggestion of 10,000 years is not very long except when viewed against the average human lifetime.)
At this point, to my delight, Davey intervened with a question.
– Why would you necessarily assume that if one intelligent life form ceased trying to communicate, another on the same planet would not immediately supplant it?
– I imagine it is because we on Earth find it difficult to believe that another life form, the chimpanzees for example, even assuming they survived whatever holocaust resulted in the extinction of Homo sapiens, would gain intelligence rapidly enough to engage in extraterrestrial communication in a reasonable span of time.
– I see. But by now you must have realized that in my universe this assumption is not valid. I am the living proof that one intelligent life form can be superseded by another. In due course I will explain to you how that came about.
After a pause to encourage further elaboration, I again continued.
– As you are likely already suspecting, estimates of the value of N vary very widely. If you are a relative optimist, and expect that the average communicating intelligent civilizations will last about ten thousand years, and that about 20 per cent of planets that evolve life will also evolve intelligent life, then you would expect that there are about a thousand civilizations in our galaxy trying to communicate with us. On the other hand, it seems that you don’t have to be much of a pessimist to conclude that the likelihood of hearing from other civilizations in our galaxy is very small indeed, perhaps one chance in a million. Of course the likelihood of a two-way conversation is smaller still, since any communication we receive may easily have been transmitted halfway across the diameter of the galaxy, or from about 150,000 light years away. At that distance, any reply would be received at least three hundred thousand years after the original message was sent!
Davey, here is a place where you can be a big help to us! Let me ask you one more time. Have you run into intelligent life elsewhere in our universe? Does that life resemble us in any way? How many instances of intelligent life have you found? Are you even able to visit more than one planet in the universe at one time? And what about . . .
– Stop all those questions, please. Before I can say anything, I have to be aware of your understanding of your situation. Otherwise, what I know could be profoundly destructive. Think about it for a minute, and you will understand what I am saying.
What could he have meant? I wondered. Does he have bad news for us, such that life would lose all its meaning? Are we destined to be destroyed by extra-terrestrial life forms? Perhaps there is a big chunk of rock headed our way that will wipe us out? Or perhaps we are destined to be the instrument of our own destruction? I at once yearned for and dreaded the answer that my continued efforts might prompt him to provide.
After a long pause it was Davey who broke into my thoughts.
– So, what you are trying to tell me is that once your forebears understood that the sun and the moon were not living beings, but rather balls of matter, a ball of gas in the case of the sun and a ball of rock in the case of the moon, they decided not to worship the sun and the moon any more, and opened a search for gods elsewhere?
– Well, not quite. Religion in the developed world had already changed a lot before the truth about the sun and moon were known. The major factor influencing religious changes seems to have been the changes in organization of human societies, which went from being many small bands of hunter-gatherers operating independently to much larger societies with one person acting as the supreme leader. I suppose that in the circumstances it seemed natural that the heavens might be organized in the same way, so that the belief in a single omnipotent God became increasingly widespread. The Jewish faith is generally reckoned to have been the first successful monotheistic religion. It got its start in about 1000 BC, well ahead of the discoveries I have just reported.
– So, it looks as though science really does not have much influence on the direction your religions take after all. I thought you were trying to tell me that science is important!
– It is important. But the influence of science did not really become key until the discipline of science had itself evolved to the point where its influence and authority became widespread. This did not really happen until some societies became wealthy enough that some of its members could afford to devote themselves to scientific enquiry. But this did not happen until long after the founding of the major monotheistic religions.
– I see. But you must admit that this whole religious business is very strange. As far as I know, my friends in my universe were never religious.
– On the contrary. It is not at all strange. For us religion was and still is a logical activity closely connected with our desire to survive. Perhaps your people had little desire to survive. I would not be too surprised as you tell me they have died out already! But I shall be very interested to learn how they could have come to exist if they had no instincts for survival.
– You must be sure not to jump to conclusions too quickly. In any case, I assume you want to stop here and meet again in about a week’s time. I wonder what you plan to talk about then. Perhaps you will tell me how humans finally came to understand their place