TCS Daily

How Lonely is Our Planet?

By Kenneth Silber - November 12, 2003 12:00 AM

Where are they?


Physicist Enrico Fermi famously posed this question when asked about intelligent extraterrestrials. If such beings exist, why have we (presumably) not been contacted or visited? Fermi's Paradox, as it is now known, is more profound than it may appear. Calculations suggest that if our galaxy has even one extraterrestrial civilization with the interest and ability to colonize new star systems, such a civilization could spread far and wide in a period far shorter than the age of the galaxy.


There are many possible solutions to Fermi's Paradox. Perhaps extraterrestrials have no interest in colonization, or destroy themselves before getting very far (but even a single exception would overthrow such explanations). Perhaps extraterrestrials have visited, in the past or present, while keeping a low profile. Maybe a ruthless galactic exterminator wipes out budding civilizations and is right now on the way here. Or it could be that Earth is the only, or at least the first, planet in our galaxy to harbor life or intelligence.


Planetary scientist David Grinspoon delves into Fermi's Paradox and other questions about extraterrestrial life and intelligence in Lonely Planets: The Natural Philosophy of Alien Life (Ecco/HarperCollins). The book provides a lively and interesting discussion of astrobiology, the scientific study of possible alien life, and of the broader history and culture of thinking about the subject. Grinspoon uses the term "natural philosophy" to emphasize the interdisciplinary and speculative nature of the issues involved.


Grinspoon is an impressively credentialed scientist with a New Age streak and an irreverent tone. He holds positions at the Southwest Research Institute and the University of Colorado, consults for NASA, and is author of Venus Revealed, a valuable overview of the science of Venus. Grinspoon shows a greater affinity than do many scientists for the Gaia Hypothesis, which likens Earth to a living organism. Thus, he thinks Mars is clearly dead, since a living planet would produce a more complex atmosphere. Similarly, he regards Venus and Jupiter's moon Io, which have complex flows of matter and energy, as relatively plausible candidates for life. By contrast, much current astrobiology focuses on worlds that have or had liquid water, such as Mars and Jupiter's moon Europa.


Overall, Grinspoon is an optimist about the possibility of finding alien life somewhere. (Such "optimism," of course, could be a form of extreme pessimism, if one gives much weight to the abovementioned exterminator scenario; but Grinspoon does not.) He notes that the plausibility of alien life is enhanced by the discovery in recent years of dozens of extrasolar planets, or exoplanets, worlds orbiting other stars. He is an enthusiast of the Search for Extraterrestrial Intelligence (SETI), which seeks radio signals or other electromagnetic evidence of intelligent aliens. He places little credence in the Rare Earth Hypothesis, which holds that complex life arose from unusual conditions here and is uncommon in the universe. Rare Earth, he argues, fails to recognize the Gaia insight that life helped shape the amenable conditions on Earth, and furthermore one can imagine planets that would be even more suitable for life.


Could it be that aliens have already arrived? Reports of alien visitations generate widespread skepticism in the scientific community. Grinspoon worries that this response is too dogmatic. He dismisses the "Face on Mars" and sees little merit in conspiracy theories. But he also warns his fellow scientists to be cautious in assuming how aliens would behave. Visiting remote places in the Southwest, Grinspoon watches the sky carefully, hoping but failing to see an alien spacecraft. He sees no reason to think cattle mutilations have an extraterrestrial cause, but regards some of them as quite mysterious.


If intelligent aliens exist, and know of our existence, there are many possible reasons why they may avoid revealing themselves to us. One scenario is the "zoo hypothesis," whereby our planet is something like a wildlife preserve set off limits by advanced aliens. Grinspoon wonders whether we are interesting or important enough to be observed in this way. He notes as an alternative the "seedling hypothesis," in which our planet is akin to one of many seedlings on a forest floor, barely worth a glance from the galactic tourists.


Lonely Planets is written in a colloquial style, replete with anecdotes and asides. Often this works well. A particularly amusing passage involves Grinspoon learning about the finding of suspected fossils in a Martian meteorite several years ago. But at times the tone becomes irritating, as Grinspoon displays his credentials as cultural hipster and political progressive. There is a gratuitous swipe against "a few Flat Earthers and Republican senators," for instance, and a suggestion that interstellar travel should involve "good weed." Also, Grinspoon's discussion of skepticism would be more convincing if he didn't repeatedly misspell the name of the magazine Skeptical Inquirer.


Grinspoon's optimism about extraterrestrials extends to a belief that they are probably wise and benevolent. He writes about how advanced beings would have transcended the dangers of self-destruction by developing their compassion and environmental awareness. But here Grinspoon disregards his own advice about assuming too much about aliens. For all we know, extraterrestrial wisdom includes advocacy of a strong defense and free-market economics. Maybe Republican senators do well in galaxy-wide elections.

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