So what should the estimates be? In class we arrived at a bunch of different numbers. Remember, that if you want the final answer to be 1 then you have to identify which term is unique (that is, it only happened here). Here are my estimates which are then explained below:

• The Astronomical Part: Basically, observations suggest that planetary formation is a natural consequence of star formation. Nearby stars exhibit dusty disks in orbit about them which are likely solar systems in the process of formation. For every star of some temperature, there is a zone around it called the habitable zone in which the temperature is right for the condensation of water vapor. The width of the habitable zone depends on the temperature of the star. If you make planets via the acretion of small grains then it is likely that one of the acreting planets will land in this habitable zone. In our case, if the sun were a cooler star we would have this class on the second planet from the sun, if it were hotter, we would be Martians. Hence, I regard the formation of planets with a liquid surface as ubiquitous.

• The Biological Part: I believe that given enough time, chemistry, mixing in the liquid surface, local concentration of organic molecules, etc, will eventually lead to a self-replicating system. That process took a billion years to happen on the earth so maybe all you need is time. But, since the planet is subject to random catastrophe, there are all kinds of problems that species have to overcome, I rate the probability of reaching intelligence as only 10% (of course it could be much smaller!).

• The Socio-Economic Part: Okay, does intelligence begat Technology? Is it the manifestation or the asshole of Intelligence? Does the capacity to destroy our planet mean that we can never really be Intelligent? And what about our lifetime as a technical civilization, will it be short or long? I assume again only a 10% probability of intelligent civilizations becoming technological (maybe most are smarter than US?). So overall, I have assumed that on only 1% of all planets with a liquid surface does a civilization which builds radio telescopes arise.

  For the lifetime I adopt the following argument:

  • 99% of all technological civilizations extinct themselves after 100 years
  • The remainin 1% survive, in harmony with their planetary resources for 1 billion years.
  • This leads to an average lifetime of 10 million years (1% of 1 billion)

• Notice, that the number of civilizations which currently exist is strongly correlated with your estimate of the average lifetime.

• Multiply it all together to get one million civilizations which now exist. This is actually a small number.

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The Electronic Universe Project

e-mail: nuts@moo.uoregon.edu