Physics Primer

I love it when someone comes along to help me make sense out of things which I had never rightly considered, or for that matter even considered at all.  Stacy Trasancos is such a person.  She has the marvelous ability to speak truth and understanding into complex areas of science and, as a great bonus, she does so from a Christian perspective.  The following is a sample of her writing which appeared at: as: Prescriptive and Descriptive Laws of Physics.  RMF

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Prescriptive and Descriptive Laws of Physics
Stacy A. Trasancos

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If someone asks you what you think of the faith and science dialogue, and the first image that pops into your mind is a tangled puzzle of equations, models, theories, laws, doctrines and dogmas, and you are not quite sure where to begin to sort it all out, then I am about to tell you one simple tip that will help.

Prescriptive and Descriptive

Stacy Trasancos

Stacy Trasancos

We will borrow two words from the late Fr. William R. Stoeger, SJ, who was an astronomer and theologian at the Vatican Observatory Research Group at the Vatican Observatory in Tucson, AZ. Fr. Stoeger made a distinction between “prescriptive” and “descriptive” laws. [1]

The word “prescribe” means to ordain, to decree, to assign, to lay down the laws. As Catholics who view science in the light of faith and profess that God created all things, we understand the laws of chemistry and physics as prescribed by God. They are complete and objective. We can hold that God created a fully interacting totality, a systematic universe. 

Science studies these prescriptive laws and seeks to understand them. So, we call the laws, hypotheses, theories, and models that scientists derive “descriptive” in that they describe what we can learn about the created order.

Laws (descriptive laws, that is) are statements of observation, such as Newton’s second law of motion which states that net force is equal to the product of mass and acceleration. Hypotheses are propositions based on observations, sometimes called educated guesses. Theories are explanations, such as kinetic theory is an explanation for the behavior of gases. Models are mental pictures. Scientific models are scaffolding, like frames that go up before walls, rooms, and décor are built around them. They are continually updated with new data, such as the atomic model has been updated over the last century.

Remember this when you learn about science: We cannot describe all of the prescriptive laws. That point is simple, but it is important in the faith and science dialogue because it demonstrates why our models, theories, hypotheses, and descriptive laws are not the ultimate explanation of cause. We are human, body and soul. We need to take in data with our senses before we can form abstractions in the mind, which is why we must practice the scientific method. And it is why we will never know everything.

It would be incorrect, even for a non-religious scientist, to call scientific descriptions of nature “prescriptive” because that would mean that the scientist lays down the laws.

Descriptive Laws Lead to New Discoveries

Here are two examples of how descriptive models have helped scientists learn new things about the created world.

The first example comes from the lessons chemistry students are taught in high school. As chemists began to discover elements in the late eighteenth century, they tried to organize them into tables. Dmitri Mendeleev, a Russian chemist and teacher, published his periodic table in 1869. He was working on a textbook for his students and trying to organize the 60 elements that were known. So he wrote the properties of the elements on cards and moved the cards around until he saw a pattern in the properties. It turns out that the properties were repeating if he arranged the elements in order of increasing atomic mass. [2]

Mendeleev left spaces in his table, however. He knew that some elements belonged in certain groups based on properties. He predicted that elements would be discovered to fill the spaces. For example, he left spaces between zinc and arsenic, and indeed gallium and germanium were discovered in 1875 and 1886 with the properties he predicted.

The second example comes from a discussion about the “eightfold way” in a college physics textbook. [3] Modern physicists have probed the nature of matter and the fundamental particles that make it up. One group of particles is called baryons. These particles were classified according to “strangeness,” a term that meant that they were strange when first discovered. The term stuck, but it is now considered a quantum number (S) to define +1, -1, and 0 strangeness. Some baryons form what is termed the “eightfold way” pattern, proposed by Murray Gell-Mann and Yuval Ne’eman in 1961.

When the strangeness is plotted against charge quantum numbers along a sloping axis, it was observed that a hexagon with middle particles appears. The symmetry for the spin-3/2 baryons predicts a pattern of ten particles that looks like the tenpins in bowling. When the pattern was first proposed, only nine particles in this group were known. The “headpin” was missing. Gell-Mann, much like Mendeleev had, predicted the existence and the properties of this particle based on the symmetry that had been found. In 1962, a team of physicists at the Brookhaven National Laboratory followed his prediction and found the missing particle.

In both cases, prescriptive laws were discovered incompletely. Descriptive models helped to guide further discovery. Science is based on faith in an ordered physical realm.

Perhaps in secular institutions the stories above seem like boring side notes in chemistry or physics classes, but for Christian students, they are rather striking bits of history. The elements that make up the periodic table and the particles that make up atoms follow prescribed laws—ordained by God—that are so ordered down to subatomic detail that scientists can guide their research based on them.

The moral is: If anyone ever tells you that science has all the answers, voice your disagreement, and be ready to explain why. You can repeat this line from the end of the physics textbook referenced above: “The main message of this book is that, although we know a lot about the physics of the world, grand mysteries remain.” [4] You might even take the chance to explain why viewing science in the light of faith is a much fuller, richer, and vastly more exciting way to understand the beauty in the natural world—because science is the study of the handiwork of God.


[1] William R. Stoeger, SJ, “Contemporary Physics and the Ontological Status of the Laws of Nature,” in Quantum Cosmology and the Laws of Nature: Scientific Perspectives on Divine Action, Second Edition, Editors, Robert John Russell, Nancey Murphy, and C.J. Isham (Vatican City State: Vatican Observatory Publications and Berkeley, CA: The Center for Theology and the Natural Sciences, 1996), 207-235.

[2] Antony C. Wilbraham, Dennis D. Staley, Michael S. Matta, and Edward L. Waterman, Chemistry (Boston, MA: Pearson Prentice Hall, 2005), 156.

[3] Jearl Walker, David Halliday, and Robert Resnick, Fundamentals of Physics Extended, 13th Edition (Hoboken, NJ: John Wiley & Sons, 2014), 1347.

[4] Ibid., 1335.


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