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The Privileged Planet
The Search for Purpose in the Universe

A review by physicist Stan Robertson, Ph.D.
8/24/05



The showing of the video, The Privileged Planet at the Smithsonian Institution earlier this summer set off a wave of criticism that continues, but at this late stage there is at last some clarity. The critics can be divided into two groups that are not exclusive: (i) those who have not seen the video and (ii) those whose religious sensibilities are offended by the premise that the universe might exist for a purpose.

This video has been reviled as thinly disguised creationism, pure religion, definitely not science, overtly anti-evolutionist, etc. It is none of these things. It is, in part, a review of much of what we know from modern astronomy. It is not concerned with biology and/or evolution. The only mentions of life are in the context of needing a planet stable for a long enough period of time for intelligent life to emerge as it has apparently done here. Religious belief is never mentioned. This video should be required for viewing by every astronomy class and by all high school students.

The video begins with a review of astronomy’s departure from the geocentric models of Aristotle and Ptolemy and the beginning of the Copernican heliocentric view. It introduces the “Copernican Principle”, which has lately become the “Mediocrity Principle”; i.e., the hypothesis that there is nothing special about our planet. It is a small rocky planet orbiting a middling star in the suburbs of a typical galaxy, which is only one of innumerable similar collections of a few hundred billion stars. This being the case, SETI (the search for extraterrestrial intelligence) is predicated on the assumption that life in the universe must be abundant. It also inspires us to look for other life within our solar system, particularly on Mars. We are also seeking diligently for evidence of the existence of other hospitable planets near other stars.

Early in the video, it is made clear that the existence of life is probably tied to the occurrence of liquid water. This, in turn, makes a terrestrial (rocky) planet in the “Goldilocks zone” the most likely place to find life. Too close to a star, water boils away and life roasts, too far and it freezes. But the search for life is not as simple as a search for water. Without providing much explanation, or making much of a case for why it should be so, the video also says that it would help to have a large moon (to prevent tidal locking of the planet’s rotation), a magnetic field capable of deflecting high energy charged particles, plate tectonics, a rotation period sufficient to keep diurnal temperature changes from extremes, etc. By twenty minutes into the video it seems that our best bet for life elsewhere would be on a very earthlike planet. Bearing in mind that a planet has to allow for the developmental stages of life as well as sustaining it later, it is not known just how much any of the requirements can be changed. We only have one example occurrence of life so far.

The writers of the book and producers and guest commentators of the video are reputable, if mostly relatively unknown, astronomers. After the first twenty minutes of an interesting and well illustrated presentation, they discuss the Drake equation, which relates the probability of occurrence of intelligent life to a set of independent chances for each of several conditions, such as the chance a planet will be found in the “Goldilocks zone”, have water, etc. They arrive at a probability of 10-15, a number so small that even given the hundreds of billions of stars in our galaxy, finding life here is quite improbable. (Depending on ones assumed values of chances for the ingredients of life, one can reach a wildly different conclusion from the Drake equation, and there is no known “correct” answer.) This leads the narrative into considering the question of purpose and design. If we are not here by chance, would there be some way of discerning this? (Folks in category (ii) of my first paragraph should be aware of the impossibility of proving their own assertion that there is no purpose, though some have come close by providing meaningless noisy objections.)

At this point the video examines some of the personal experiences and motivations of the authors. Guillermo Gonzales relates his near religious experience of observing a total solar eclipse and first understanding the full implications of being able to observe such a thing. This ties in later with a hypothesis that we are here with a purpose of our own - to learn of the universe - and we have been positioned such that we can! Had I been making this video, I would have deferred this until after considering more of the “fine tuning” of the universe as a whole, because this “fine tuning” is already well known and accepted within science.

Though there are still a few die-hards among cosmologists, it is accepted that the relative strengths of gravitational and nuclear forces are such that gravity can aggregate the materials of stars and nuclear processes can burn them, produce the heavy elements needed for our existence, scatter them among the stars and do this all on a time scale that has let life develop here. A small shift in the energy levels of carbon nuclei would be sufficient to change stellar lives to the point of making life impossible. The quantum fluctuations in the early universe are of just such a size as to let galaxies form at the right stage of the expansion of the universe. There is no accepted physical theory of how this all came to be “just so”, and, in fact, the argument has been reversed. It is accepted that theories must honor the “Weak Anthropic Principle”, which is that an acceptable theory of origin of the universe must accommodate the fact that we exist.

Once it is understood that the universe is finely tuned in ways that permit our existence, then it is logical to consider other things about our existence that seem, at best, fortuitous. The video makes the point that some things essential for our existence, such as the electromagnetic spectral windows through our atmosphere, our position in the solar system and in the galaxy are such that we are positioned to enable us to learn. Solar eclipses, gratuities of a large moon, have yielded an understanding of how stellar absorption spectra are produced, permitted the discovery of helium and confirmed aspects of general relativity. Had we been so unfortunate as to live within a globular cluster or the galactic bulge, we could know but little of the universe even if we could exist there. So the question is, why are the things that are conducive to life also conducive to knowledge? Is it our purpose to learn?

I once read a story about a fellow condemned to death by firing squad. Miraculously, fifty marksmen simultaneously missed. It would be a bit strange if he failed to wonder just why he was still alive. We are here after a similar bit of good luck in the fine tuning of the universe and our position within it. Under the circumstances, it should be permissible to choose to think of the earth as something more than a pale blue dot lost in a dark cosmic sea.