What Are the Chances of Intelligent Life Elsewhere in the Universe?

The Drake Equation, mentioned in Atkinson (2008) points at a theoretical possibility of approximately 1,000 planets other than Earth being home to intelligent life. As such, it has been the guiding force of many enthusiasts who scan the night sky in search for "others like us." The more recent scientific view, however, is considerably less optimistic, placing a chance of an intelligent life developing anywhere else in the universe at 0.01% over the last four billion years. The time period is not accidental: it is the time when most Sun-like stars in the universe have come to maturity.

Expressed by scientists like Andrew Watson (in Atkinson, 2008) and Stephen Hawking (2008), the view that intelligent life is highly unlikely to develop in the universe is based on a number of factors, among the most important of which is the fact that intelligent life on Earth has developed rather late in the solar system's overall existence. Both Watson and Hawking predict that while the Sun will not undergo any significant changes in its nearest cosmological future, the changes in its inner composition will produce enough variations that life on Earth will be no longer possible after about one billion years from now. Considering that it took around four billion years for intelligent life to emerge in the first place, the remaining stretch of time appears comparatively short.

Watson bases his theory on the Fermi Paradox, which points at the apparent contradiction between the number of intelligent species in the universe and the lack of interaction between them, or at least detection of one by another. Watson develops his theory by pointing out that the intelligent life - at least in the case of humans - needs four highly complex steps to develop, specifically the emergence of single-celled organisms, then complex-celled organisms, then specialized cells allowing for complex life forms, and finally intelligent life with an established means of communication (Atkinson, 2008). The farther up the chain of these events, the less common each one is to occur - and since no subsequent step can occur without the preceding steps taking place, it makes the emergence of intelligent life highly unlikely overall.

In addition to Watson's theory, Neil Rieck (2008) has developed his own equation, which he calls Rare Earth Equation, based on which he claims that chances of intelligent life existing elsewhere in the universe are miniscule. He includes a number of factors into his equation that are missing from Drake's equation, specifically the existence of metal-rich planets in habitable star and galactic zones, percentage of planets with a large Moon-like natural satellite, and percentage of solar systems with Jupiter-sized gas giants. The last two factors are essential, according to Rieck, to reduce the risks of catastrophic mass extinction events due to a habitable planet being impacted by large comets or meteorites. This argument follows the one presented by Watson and Hawking, both of whom claim that the outer planets of the Solar system are the main reason Earth has experienced mass extinction events comparatively rarely in its existence after the planetary system was fully formed.

References

Atkinson, N. (2008). The odds of intelligent life in the universe. Universe Today (April 19). Online at http://www.universetoday.com/2008/04/19/the-odds-of-intelligent-life-in-the-universe/

Hawking, S. (2008). Life in the universe. Public Lectures (2008). Online at http://www.hawking.org.uk/lectures/life.html

Rieck, N. (2008). Is Earth home to "rare intelligent life"? Online at http://www3.sympatico.ca/n.rieck/docs/rare_intelligent_life.html