by Dr. Guillermo Gonzalez
If the universe were not measurable, scientific study would be impossible. Astronomy, biology, chemistry, cosmology, geology, physics, and the other disciplines of science would be no less quixotic than alchemy or astrology. Science would not—could not—shed much light in the cosmic darkness.
Most scientists take the measurability of the physical realm completely for granted: It is measurable because scientists have found ways to measure it. Scientists (myself included) may take pride in our ability to make measurements––especially those measurements requiring ingenuity, persistence, and skill––but why take the universe’s measurability for granted? Is there any deep significance to the measurability of the universe? The answer springs from the very foundations of science, from the philosophical assumptions (chiefly drawn from the Judeo-Christian Scriptures1) on which scientific endeavor rests. These assumptions include, among others, the existence of a theory-independent external world, the existence of order in the external world, the reality of truth, the validity and reliability of the laws of logic and mathematics, the basic reliability of sense perception, and the adequacy of the human mind to comprehend the universe.2 The Judeo-Christian vision of reality predicts a unique correspondence between the physical universe and the human mind.
By identifying the aspects of measurability humans cannot influence or control, one can determine (at least roughly) whether or not the measurability of the universe requires supernatural fine-tuning, and if so, to what degree. This study begins with a look at the nearby cosmos and from there moves outward in space, backward in time.
The Measurability of the Earth
One of the characteristics that makes Earth such an ideal “recording device” is its built-in set of time markers––cyclical rhythms on time scales of days, months, seasons, years, centuries, periods, eras, and eons. Humanity could have found itself in a far less measurable place. The Moon, for example, does not have active weather, seasons, or tectonics, and therefore offers few time markers. The Moon looks ancient, yet ageless. Jupiter and the other gas giants have active weather, but they lack any solid surface on which to record their rhythms and events. The thin crust of the Earth provides not only a safe and comfortable place for living creatures of all kinds, but it also serves as the planet’s information storage space. The deep, hot interior of the planet, the atmosphere, and the oceans are all too fluid to preserve much of the past.
Earth’s cycles provide the steady beat of time markers, with other, more subtle, fluctuations superimposed. Because of seasonal changes in weather and plant life in a given locale, growth and deposition phenomena leave easily distinguishable (and measurable) features. Growth rings in trees not only yield information on the rain and temperature for a given season, but they also provide a unique tool for measuring the carbon-14 content of the atmosphere, which is modulated, in turn, by the sunspot cycle. Research on tree rings gives astronomers information about solar variations on a wide range of time scales, from decades to millennia.
Snow deposits in Greenland and Antarctica have created a four hundred-thousand-year record of the composition of Earth’s atmosphere. 3 Ancient air bubbles trapped within these deposits allow us to measure the concentration of carbon dioxide and other gases in past eras. The snow deposits give us a measure of ancient dust levels, which are indicative of large volcanic eruptions or very dry conditions. They also enable us to measure the ratios of three oxygen isotopes, which indicate the mean global temperature in past epochs. According to a very recent study, nitrate spikes in Antarctic ice deposits may help us trace supernova events (gigantic star explosions) of the past thousand years.
Certain features of the ocean floor allow us an even longer-range view, hundreds of millions of years back into Earth’s history. At the mid-ocean ridges (“spreading centers”), new sea floor is produced when molten rock upwells from the hot mantle below. When the molten rock solidifies it records the state of the earth’s magnetic field at that time. By studying these sea-floor records at varying distances from the spreading centers, oceanographers can “read” the history of fluctuations in Earth’s magnetic field. A phenomenon so subtle as to be unnoticeable in everyday life is reliably recorded and preserved for later discovery and deciphering.
Ancient “tidalites” (tidal sediment layers) and coral, mollusk, and stromatolite growth layers record the lunar and solar tidal cycles, giving us unique data on the length of terrestrial days and lunar months in ancient times. Such data tell us that 500 million years ago, a day was about 20 hours long and a month was about 27.5 (present-epoch) days.4
Meteorites that have hit the earth provide another treasure trove of data (preserved for billions of years) waiting to be unlocked. Many meteorites come from the asteroid belt, where collisions between asteroids send shards hurtling throughout the inner solar system (planets from Mars inward) and occasionally to the earth. Fragments falling on the ice fields of Antarctica are the best preserved ones, and their dark appearance makes them easy to distinguish against the uniform blue-white background. Today, a meteorite’s individual grains, each measuring less than a millimeter in width, can be separately analyzed. These grains yield invaluable clues to the sources of short-lived (now extinct) “radionuclides” present in the gas-and-dust cloud from which our sun and solar system formed. They also give us clues to the timing of certain key events in the formation of neighboring planets.
Even more amazing is the discovery that meteorites carry what appear to be individual interstellar dust grains, each from a different star that existed before the Sun. These dust particles give us rare and important data on the chemical history of the Milky Way. It appears that as part of God’s grand design of the cosmos, He has provided a method of collecting, preserving, and delivering to our doorstep tiny bits of distant (both in the spatial and temporal sense) stars. What more could an astronomer ask for?
On a less grand scale, small bits of the moon and Mars have been blasted to the earth by large impacts. The most famous of these is the Martian meteorite, ALH 84001 that stirred much media attention a few years ago. The Moon probably contains a rich reserve of unaltered planet shards from the early history of the solar system. One might think of the Moon as the earth’s attic, where ancient artifacts are stored and forgotten, perhaps to be retrieved one day.
The Measurability of the Sun
Total eclipses of the Sun as seen from the surface of the earth may be described as both “useful” and “exceptional.”5 Apart from the deep awe they inspire in every people group from remote tribes to astrophysicists, these eclipses allow us to study the Sun’s corona, test general relativity, and calculate the slowdown of the earth’s rotation. They are exceptional in that they are nearly “perfect;” that is, the earth and Moon are similar in size, the solar and lunar profiles on the sky are nearly perfect circles, and the Sun appears to be larger when it is viewed from Earth than when it is viewed from any other planet with moons. The likelihood of finding this combination of features is remote. Of the roughly 65 natural satellites (moons) in the solar system, none even comes close to producing such clear and spectacular eclipses.
What’s more, humans live at a special time with respect to the observability of total solar eclipses. Since the Moon is spiraling away from Earth and the Sun is swelling due to its changing internal structure, such eclipses are possible only for a relatively brief time span. They will continue only for about 250 million years. That may seem like a long time, but it constitutes only approximately 5% of Earth’s history.
The Sun’s radiation conveys a wealth of information. By observing its spectrum, researchers learn about the Sun’s composition, surface temperature, and surface gravity. This “readable” spectrum is not unique to the Sun, but the Sun’s spectrum is nearly optimal in terms of measurability and the number (and abundances) of chemical elements it reveals.
This optimal quality of the Sun’s measurability derives from characteristics other than its proximity to Earth and the large number of photons arriving at Earth-based instruments. In comparison to the spectra of other stars with similar “signal-to-noise ratio” (data quality), the Sun’s spectrum contains more extractable information. The Sun’s particular surface temperature and its relatively low luminosity allow for the extraction of more information. The remarkable convergence of these just-right characteristics maximizes its readability.
The Astronomical Realm
The light sent to Earth from sources outside the solar system contains a wealth of information about stars, nebulae, galaxies, and even the intervening matter. Using various techniques and instruments, astronomers have used that light to map out most of the Milky Way disk, clearly delineating its spiral arm structure.
The measurement of the three-dimensional space motions of stars in the Milky Way is possible only because stars can be treated as if they were mathematical points. This feature allows astronomers to measure the relative positions of stars very precisely, and it means that stars can be used as simple probes of the Milky Way’s gravitational field. If stars were larger and the distances between them smaller––like nebulae, for example––then the mathematics would be much more complex. Stars’ positions and other features would be far less measurable, because their light would be spread over a larger volume of space. Also, if the Milky Way contained fewer stars, it would yield fewer and more obscure clues about its history and structure.
Astronomers have discovered that certain light sources are particularly useful as “standard candles” (see sidebar). Examples of standard candles are Cepheid and RR Lyrae variable stars. The pulsation period of a Cepheid variable is related to its intrinsic luminosity in a simple way. By measuring the period and mean apparent brightness of a particular Cepheid variable star, one can easily calculate its distance. Because of the simplicity and consistency with which these objects operate, they provide invaluable reference points, or units of measure. Astronomers rely on this important data to reveal some of the fundamental constants of the universe.
The cosmic microwave background radiation, first detected in 1965, has enabled cosmologists to extract information on enormous size- and time-scales. With the launch of the Cosmic Background Explorer (COBE) satellite in 1989, astronomers were able to make measurements precise enough to confirm several predictions of the Big Bang theory (a theory consistent with the Bible) and effectively kill both the Steady State hypothesis and the oscillating universe hypothesis. Atheistic cosmologists as a way to avoid a beginning for the universe had favored these hypotheses. Two upcoming space missions, the NASA Microwave Anisotropy Probe (MAP) and the European Space Agency (ESA) Planck Surveyor, promise orders of magnitude improvement over the measurements the pioneering COBE satellite recorded. The background radiation is sufficiently intense that we can measure it precisely with modern instruments, but not so strong that it is unaffected by processes shortly following its creation. Therefore, we can learn about certain parameters of the universe at very early times, constrain some aspects of fundamental physics, and garner a glimpse at early large-scale structure and formation.
As the universe ages, the background radiation will become less measurable. First, the continued expansion of space-time will cause it to become less intense and more redshifted. Second, as stars continue to form in the Milky Way, they will contribute to greater foreground contamination, resulting in greater difficulty in measuring the ever-fading background.
In terms of its mass, the Sun is among the top 10% most massive stars in the solar neighborhood. 6 Aside from obvious questions of habitability, what if humans were attempting to scan the skies from a planet orbiting one of the less massive stars, one of those among the 90% majority? What would they be able to detect and measure? The most fundamental ruler in their astronomical “tool chest” would be less effective. It is the method called stellar parallax. Earth’s inhabitants can use the changing position of the earth in its orbit around the Sun to detect the apparent reflex motion of nearby stars relative to distant background stars. By this method they can measure the distance from the earth to those nearer stars.
M dwarfs are the most common type of star in the Milky Way. The habitable zone comprises the place around a star where liquid water can exist on the surface of a terrestrial-like planet continuously. The estimated diameter of the habitable zone around an M dwarf is only about 10% that of the zone around the Sun, the zone in which Earth resides. Therefore, for a planet orbiting an M dwarf, the effectiveness of the stellar parallax method would be severely diminished. In fact, astronomers on such a planet would be able to observe only one-thousandth the volume of space Earth-bound astronomers can observe. The distances to many rare types of stars, such as O and B stars, and Cepheid and RR Lyrae variables, would remain a mystery, and information they provide would be inaccessible. Clearly, M dwarfs would be less hospitable for life, and the cosmos far less measurable from their environs.
Since measurability is not a requirement for habitability, one cannot invoke the Anthropic Principle7 to make the remarkable measurability of the universe seem less remarkable. Evidence suggests that the universe was designed not only for human habitability but also for human measurability and comprehensibility. The same processes and features that make Earth habitable also make and preserve a record of activity and provide a means for measurement. Those very places in the Milky Way that would be most dangerous to humans (e. g., the galactic center, globular clusters, and spiral arms) also offer the poorest visibility and opportunity to make measurements. Does it seem a mere coincidence that Earth’s location in the Milky Way affords an optimal view of most of the universe? Humanity’s home planet is a comfortable porch from which curious humans can gaze out to the ends of time and space.
This argument allows us to ascribe purpose to any fine-tuned, measurable aspect of the universe, such as stars and galaxies, earthquakes, neutrinos, and the Moon. If anyone asks, “Why are there so many stars and galaxies in the universe?” One can respond with double impact: Not only is a universe as big as this one required for any kind of life, but only a vast number of stars and galaxies permits intelligent creatures to measure (reliably) the basic parameters of the universe. Earthquakes are important not only because life needs the effects of plate tectonics but also because they allow us to probe the internal structure of the Earth, which could not be done any other conceivable way. Neutrinos give us a way to measure the temperature of the sun’s core and to study the details of neutron star formation in supernovae explosions. The Moon records some of the early history of the solar system and takes part in producing wonderful eclipses. And so on.
Of course, this consideration brings us to the deeper, theological question: Why would the Creator make the universe so measurable? What’s the point of allowing humans to measure the characteristics of the universe? To those who hold a Christian worldview, the answer is clear. In fact, the Bible explicitly states it: “For since the creation of the world God’s invisible qualities, His eternal power and divine nature, have been clearly seen, being understood from what has been made, so that men are without excuse” (Romans 1:19-20).
Sidebar: Standard Candles
Astronomers employ some types of stars as “standard candles.” These are stars that have luminosities that are in some way standard. As a simple everyday example of a standard candle, consider an ordinary 100-watt light bulb. Because a light bulb has a constant luminosity (or intrinsic brightness) we can estimate its distance from us if we can measure its apparent brightness. This technique only works if we have good reason to believe the luminosity of a given light source is some standard value. For a distant light bulb, one can verify its luminosity by observing it with a telescope and looking for the phrase “100 watts.” Of course, this does not work with stars, but the principle is similar.