The Right Place at the Right Time — August 12th, 2008 by Guillermo Gonzalez
On the first day of this month, thousands of people traveled to a narrow strip of land stretching across Siberia, Mongolia and China. Their common purpose was to observe an uncommon phenomenon—a total solar eclipse. However, minutes before totality, observers in one popular location in China were despondent. Clouds were covering the Sun. Then, just moments before the big show began, the clouds parted like curtains opening to reveal an actor on a stage. The sky darkened and the Sun’s pearly white corona became visible. When it was over, the observers broke into applause—a scene that was repeated at many other locations along the eclipse path.
People go to great lengths to witness events like this. Not only did they have to travel (considerable distances, in some cases) to position themselves along the narrow eclipse track, they also needed to maneuver to avoid cloud cover. No one on the ground would have seen the eclipse if the clouds had prevailed along the entire eclipse path.
Indeed, the prevalence of cloud-free weather on planet Earth enables us to view not only eclipses but also stars, galaxies, and other planets. Although we tend to take this for granted, it certainly isn’t the case everywhere. In fact, we have several examples in our Solar System of worlds with nearly opaque atmospheres—Venus, the giant planets, and Titan—where the kinds of celestial observation we enjoy on Earth would be impossible.
And Earth’s advantages extend further. It takes more than a transparent atmosphere to view total solar eclipses. A suitable viewing planet must also have a moon large enough and close enough to just cover the Sun’s bright disk. Although the Sun is much larger than any moon, our Moon appears to match it in size when viewed from Earth, this match resulting from the equivalent size-to-distance ratios (1:400).
Are these circumstances that allow us to observe the best solar eclipses in the Solar System just a lucky coincidence, or do they point to something larger? In 1999, I addressed this question in a research paper [1], where I argued that our privileged view of solar eclipses does indeed point to a larger principle of profound significance. Namely, the Earth’s ability to serve as a platform for viewing total solar eclipses seems to be intimately linked to its ability to support living viewers—us.
The argument goes like this. First, Earth must be located an appropriate distance from the Sun in order for liquid water to exist on its surface, a necessary condition for life. This restricts the angular size that the Sun can subtend in our sky. Second, the presence of a large nearby moon stabilizes the tilt of Earth’s rotation axis, resulting in less extreme temperature variations and a more habitable climate. Small moons like the two around Mars do not have this effect. When examined quantitatively, these constraints imply that habitable planets are also likely to be good viewing platforms for solar eclipses. In other words, the laws of physics seem to require that habitable planets are more likely to feature good views of solar eclipses than those that are less habitable.
Were this the whole story it would be interesting enough. But it isn’t. As it happens, total solar eclipses are not only awe inspiring events, but they are also scientifically important. A total solar eclipse in 1919, for example, served as the first test of Einstein’s General Theory of Relativity. More generally, our large moon has played an important role in advancing scientific understanding since the time of the ancient Greeks. The Privileged Planet, a book I authored with Jay Richards [2], describes many more examples of these connections between the conditions needed for life and those that have been instrumental for scientific discovery in a number of fields, including the Earth sciences, astrophysics and cosmology.
I’ll describe one more example here, this one from cosmology.
The universe as a whole has changed dramatically since its birth: star formation is slowing; galaxies are less dusty; galaxy collisions are less frequent; and the temperature of the intergalactic medium is dropping. Not only is the universe expanding, causing galaxies to move apart, but that expansion is accelerating.
To learn about the bulk properties of the universe and its early history, astronomers rely on observations of a few key things: other galaxies, so-called “standard candles” (objects with known luminosity), the elemental composition of the oldest stars and galaxies, and the cosmic background radiation (CBR). The CBR is the residual radiation from an early time when the universe was much hotter and denser. Its discovery in 1963 confirmed a prediction of the Big Bang theory, implying that the universe had a beginning.
So, since the universe is constantly changing, how does its observability change over its history? In short, it offers a relatively brief window of opportunity for doing cosmology, and we happen to find ourselves in that window. In the future, galaxies will be farther apart; Classical Cepheids (an important type of standard candle) will be less common; and the CBR will be fainter as a result of the continuing expansion of the universe. When the universe is a few times its present age, the evidence of the Big Bang will no longer be available for observation. With this realization in mind, Abraham Loeb recently wrote, “The accelerating universe makes the study of cosmology a transient episode… ” [3].
Not only is this the best period in history for doing cosmology, it also seems to be the only period that can sustain living, breathing cosmologists. The early universe was a much more dangerous place, and in the future Sun-like stars and the geologically important radioisotopes will be rarer, both important requirements for intelligent life. So, it seems that the best time for observing is also the best time for observers!
But why should this be so? It isn’t easy to explain this in terms of mere coincidence because, on top of explaining why the universe seems set up for life, we now need to explain why it seems set up for discovery. The simple solution, of course, is the obvious one—that the universe was designed both for intelligent life and for discovery.
Is this idea testable?
I think it is. For instance, if additional examples of the link between life and discovery are found, this will strengthen the thesis, as would additional evidence for known examples. On the other hand, if additional study weakens the examples we have described, or shows them to be wrongly interpreted, then the thesis is weakened.
Interestingly, since The Privileged Planet was published, a technical paper has appeared [4] that supports one of our claims—that we are living during the best time in the history of the universe to study cosmology. In fact, that paper—which makes many of the points we made in Chapter 9 of our book—was judged important enough to receive an award.
In the latest issue of Science, a paper describing simulations of planet formation indicates that planetary systems like ours may also be quite rare. [5] Commenting on these results in New Scientist, Jeff Hecht said, “Our solar system is a Goldilocks among planetary systems. Conditions have to be just right for a disc of dust and gas to coalesce into such a set of neatly ordered planets… ” [6].
So as our understanding of cosmology and astrobiology grows, we keep bumping into this design idea at every level. We find ourselves in a universe that looks as though we were anticipated… and as though we were meant to know that.
[1] Gonzalez G (1999) Wonderful eclipses. Astronomy & Geophysics 40: 18-20.
[2] Gonzalez G and Richards JW (2004) The Privileged Planet. Regnery.
[3] Loeb A (2008) Is there an end to cosmology? Astronomy, August 2008, p 29.
[4] http://arxiv.org/abs/0704.0221