ALIEN-hunters, take heart. A long-standing argument against finding intelligent extraterrestrial life has been roundly challenged.
The theory, suggested by astrophysicist in the 1980s, assumes set timescales for two processes: the life cycle of a star, and the emergence of complex life. By statistically combining the two it concludes that complex life takes longer to emerge than the life-friendly duration of most stars. If so, we could be alone in the galaxy.
Many scientists were unhappy with this conclusion, but could not disprove it. Now a trio of Serbian researchers is disputing Carter鈥檚 starting assumptions (Astrobiology, ). Milan 膰irkovi膰 and colleagues at the University of Belgrade and Belgrade Astronomical Observatory say there is no reason to assume life evolves only gradually. They argue life could evolve in fits and starts 鈥� mirroring an evolutionary theory called .
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They also point out that the rate of evolution is intimately connected with a planet鈥檚 environment, such as the kind of radiation its star emits. And they say that occasional catastrophic events could reset the 鈥渁strobiological clock鈥� of regions of the galaxy, forcing biospheres to start over. 鈥淓arth may be rare in time, not in space,鈥� the researchers say.
鈥淭hey definitely have a point,鈥� says Mario Livio of Johns Hopkins University in Maryland, who challenged Carter鈥檚 theory in a 1999 paper. 鈥淲e shouldn鈥檛 give up before we even start searching.鈥�