?Say, "Have you thought: if God made the night perpetual until the Day of Resurrection, which god besides God would have provided you with light? Do you not hear?" Say, "Have you thought: if God made the daylight perpetual until the Day of Resurrection, which god besides God would have provided you with a night for your rest? Do you not see?" -Quran 28:71-72

?In the creation of the heavens and the earth and the alternation of night and day, there are signs for those who understand.? -Quran 3:190

?We showed Abraham the kingdom of the heavens and the earth so that he may attain certainty.? ?Quran 6:75

For the first time in 1992, planets outside the solar system (exoplanets) were discovered orbiting a radio pulsar, a rotating neutron star www.nature.com). The first definitive confirmation of an exoplanet orbiting an ordinary main-sequence star came forth in 1995 www.nature.com). About 200 exoplanets, mostly hot gas giants, have been discovered since then. NASA's Kepler Mission, Space Interferometry Mission, Terrestrial Planet Finder, European Space Agency's Darwin and Gaia, and France's COROT are all gearing up for a thrilling celestial hunt for exoplanets. For instance, the Kepler Mission www.kepler.arc.nasa.gov) is scheduled to lift off in November 2008 to search for Earth-like planets in habitable orbital zones around stars:

?The Kepler satellite will orbit the Sun and study some 100,000 stars for four years, looking for planets that are similar in size to Earth and in similar orbits around their stars. Only planets with orbits in this so-called "habitable zone," where it is not too hot and not too cold, could have liquid water, scientists say. And liquid water is seen as a necessary ingredient for life as we know it? www.space.com).

The Privileged Planet: How Our Place in the Cosmos is Designed for Discovery proposes that the rare conditions that allow intelligent life to flourish on Earth (habitability criteria) also make the planet a uniquely well suited platform that permits intelligent life to study the universe (measurability criteria). From the Privileged Planet website:

?Elsewhere, you might learn that Earth and its local environment provide a delicate, and probably exceedingly rare, cradle for complex life. But there's another, even more startling, fact, described in The Privileged Planet: those same rare conditions that produce a habitable planet-that allow for the existence of complex observers like ourselves-also provide the best overall place for observing. What does this mean? At the least, it turns our view of the universe inside out. The universe is not "pointless" (Steven Weinberg), Earth merely "a lonely speck in the great enveloping cosmic dark," (Carl Sagan) and human existence "just a more-or-less farcical outcome of a chain of accidents" (Steven Weinberg). On the contrary, the evidence we can uncover from our Earthly home points to a universe that is designed for life, and designed for discovery? www.privilegedplanet.com).

Allow me to illustrate a few instances of the correlations between habitability and measurability:

1. The atmospheric mixture (the right proportion of the right chemicals such as ozone, oxygen, carbon dioxide, etc.) of Earth protects and flourishes life (habitability criterion), and the same mixture is stunningly so clear and transparent that it allows observers to use the night sky to study moons, planets, stars, celestial mechanics, nebulae, supernovae, and other astronomical phenomena even in the distant reaches of the visible universe (measurability criterion). Many planets seem to either lack clear and transparent atmospheres or lack atmospheres altogether.

Did anyone watch the sci-fi movie Pitch Black imdb.com)? Three suns would continuously illuminate the exoplanet for 22 years. The three suns would then align in such a way that the planet would get eclipsed by another giant, ringed planet in the system, tossing the eclipsed planet into uninterrupted pitch darkness for another 22 years. Planets like that in multiple-star systems are gravitationally unstable, yet are possible, given a certain celestial setup. If there were no night sky, no reasonably frequent alternation of day and night (i.e., in reasonable relation to a certain length of average human lifetime), or no transparent atmosphere, would we have ever learnt Kepler?s laws of planetary motion, discovered Galileo?s moons of Jupiter, confirmed Einstein?s general relativity, landed on the moon, known the Big Bang, launched satellites to study the cosmic microwave background radiation (the remnant of the explosive creation of space-time), and postulated possible cosmological geometries, to name a few? Reasonably frequent alternation of dark nights and lighted days and a transparent atmosphere promote scientific progress of intelligent life on a planet.

2. The solar system is located about halfway between the galactic center and the edge of the galactic disk and in the mid-plane of the Milky Way galaxy when viewed edge on. As we approach the galactic center, the risk of supernovae, short-lived stars, black holes, quasars, gamma ray bursts, and other violent cosmic events proportionally increases. Also, closer to the center, the night sky would be much brighter and thus would obscure the view of background stars and other celestial objects from observation. As we travel out from the center, the metallicity of stars proportionally declines, resulting in increasingly lower likelihood of terrestrial planet formation. The solar system?s location within the Milky Way galaxy is exceptional. Our planet is not located in the violent central galactic bulge, not near a source of gamma radiation, not in a gravitationally unstable multiple-star system, not near a pulsar, and not near a star too small, too large, or soon to explode into a supernova (habitability criterion). Our planet is located precisely in that region of the Milky Way?s spiral arm that permits telescopes to pierce into the background stars and the farthest reaches of the visible universe. Our view of the cosmos from Earth is free of obstruction by dense star clusters and by diffuse gas found in other regions of the galaxy (measurability criterion).

3. The Earth has a magnetosphere that shields life from solar flares (habitability criterion), and the stable magnetic field facilitates terrestrial and aerial navigation (measurability criterion). Can we imagine leading the expansion of the Arabian Empire through the African Sahara in the 8th century AD without a compass, or flying United Airlines from Los Angeles to Sydney on an Earth without a magnetic field?

I have offered a brief and an admittedly incomplete analysis of many such exceptional and fascinating correlations between habitability and measurability. Our planet seems to be exquisitely fit not only to support life but also to offer us the best platform or laboratory for probing the universe. It is as if the Earth were specially designed both for life and for scientific discovery (Privileged Planet hypothesis). The Privileged Planet hypothesis undermines the Copernican Principle and the Principle of Mediocrity in the philosophy of science. The Principle of Mediocrity holds that there is nothing special about Earth and the human race. It is a Copernican Principle, which maintains that no special observers should be proposed.

The data from exoplanet space missions serves as a test of the Privileged Planet hypothesis. Are there more Earth-like planets that have conditions suitable for intelligent life to flourish and conditions suitable for the life forms to discover the marvels of the universe? Is there something strangely extraordinary about the correlation between the Earth?s habitability and measurability conditions? Are our planet and our existence special and purposeful? With forthcoming data from exoplanet space missions, it would be interesting to see how the hypothesis fares against orthodox philosophical notions that maintain that the human race?s existence is unexceptional in the cosmos. Stay tuned.

Nadeem

References (excludes web links)

Gonzalez, Guillermo, and Jay W. Richards. The Privileged Planet: How Our Place in the Cosmos is Designed for Discovery. Washington, DC: Regnery Publishing, Inc., 2004.

Lead Author's Bio www.public.iastate.edu discovery.org)

Guillermo Gonzalez is an Assistant Professor of Astronomy at Iowa State University. He received his Ph.D. in Astronomy in 1993 from the University of Washington. He has done post-doctoral work at the University of Texas, Austin and at the University of Washington and has received fellowships, grants and awards from such institutions as NASA, the University of Washington, Sigma Xi (scientific research society) and the National Science Foundation.

Gonzalez has extensive experience in observing and analyzing data from ground-based observatories, including work at McDonald Observatory, Apache Point Observatory and Cerro Tololo Interamerican Observatory. He is a world class expert on the astrophysical requirements for habitability and on habitable zones and a co-founder of the Galactic Habitable Zone (GHZ) concept. Astronomers and astrobiologists around the world are pursuing research based on my work on extra solar planets host stars, the GHZ, and several discoveries pertaining to stellar abundances.

Gonzalez has also published over sixty articles in refereed astronomy and astrophysical journals including Astronomy and Astrophysics, Monthly Notices of the Royal Astronomical Society, Astrophysical Journal and Solar Physics. His current research interests in astrobiology focus on the "Galactic Habitable Zone" which captured the October 2001 cover story of Scientific American, and the properties of the host stars of extra solar planets. He also is the co-author of the second edition of "Observational Astronomy" an advanced college astronomy textbook..

In 2004 he co-authored The Privileged Planet: How Our Place In The Cosmos Is Designed For Discovery with Jay W. Richards.