Which change is more significant: tripling a number or increasing a number by 0.04 percent. If you guessed tripling a number, your answer probably matches the replies of the vast majority of people. Yet, from a scientific perspective, the question cannot be answered without additional information. Two discoveries over the last few months demonstrate the problem.
As I discussed last week, detailed observations of large elliptical galaxies caused astronomers to revise their estimate of the number of stars in the observable universe—by tripling it. This sounds like a large change because the error bars on these estimates are often omitted. To be more specific, astronomers typically estimate there are somewhere between ten billion trillion to one trillion trillion (or 1022 to 1024) in the universe. Given this large error range (a factor of one hundred), a change by a factor of three is not significant.
Likewise, in August 2010, researchers found evidence that the solar system (and thus the Earth) might be two million years older than previously thought.1 Such an increase may seem irrelevant when compared to the accepted age of 4.5 billion. However, astronomers measure the age of the solar system with much greater precision than they do the number of stars. Scientists date the minimum age of the solar system to be 4.5695 +/- 0.0002 billion years.2 Consequently, a change of 2 million years (or 0.002 billion years) represents a change ten times larger than the error bars.
So is this significant change an example of bad science? Not at all.
First, one must realize how astronomers date the age of the solar system. Although no objects come with a date stamped on them, we know that many of the comets and asteroids formed at the start of the solar system. Pieces of asteroids and comets break off and enter Earth’s atmosphere as meteorites. Astronomers can determine a meteorite’s age if it matches certain criteria. More specifically, astronomers look for inclusions in the meteorites that date to the earliest stages of the solar system and then measure a date for the inclusions using various radioisotope dating techniques. From the oldest inclusions found, astronomers then determine a date for the birth of the solar system by adding the time it takes for the inclusions to form (around one million years). The addition of two million years to the solar system’s age does not reflect poor measurements or a change in our understanding of planet formation. Rather, it means that astronomers found a meteorite with inclusions that were two million years older than previous finds. Thus, the change reflects an improvement in the data used to study the early solar system.
Rather than representing defects in the scientific enterprise, the changes in the estimated number of stars and in the age of the solar system demonstrate how our understanding of the universe (and humanity’s place in it) continues to grow. The detailed knowledge scientists have about the early solar system reveals the remarkable set of events that transpired to ensure Earth’s habitability. The heavens do indeed declare the glory of God.
- Audrey Bouvier and Meenakshi Wadhwa, “The Age of the Solar System Redefined by the Oldest Pb–Pb Age of a Meteoritic Inclusion,” Nature Geoscience 3 (September 2010): 637–41.
- Joel Baker et al., “Early Planetesimal Melting from an Age of 4.5662 Gyr for Differentiated Meteorites,” Nature 436 (August 25, 2005): 1127–31.