SCIENCE MATTERS - 'Theory' has specific meaning


It's no wonder the public is confused and often misled about the use of the word "theory" in science. Its meaning to the scientific community is significantly different from its colloquial usage.

I recently witnessed this disparity while watching a detective story on TV. A detective stated he had a theory about a case he was working on. My immediate responds was, "No, you have a hypothesis."

To begin with, it is important to understand that all scientific knowledge is tentative. Scientists must be open to new information that might invalidate accepted ideas. This is one of the great strengths of the scientific endeavor.

It must be said, however, different bodies of knowledge have varying degrees of certainty. A hypothesis is among the most tentative kind of statements that can be made.

It is formulated from a limited amount of data. This does not mean it is a wild, unsupported guess. It is simply a work-in-progress. It is a best attempt at characterizing an, as yet, ill defined pattern.

Hypotheses must be meaty enough they can be tested. Scientists formulate them for the purpose of guiding further experimental investigation. The resulting data will either validate or invalidate assertions made in the hypotheses.

Theories are at the other end of the spectrum. They are the least likely statements to be overturned. They are organizing principles often integrating concepts from multiple disciplines. Consequently, the implications of theories are profound.

The Atomic Theory of Matter is one such broad ranging theory. Everything known about chemistry, electronics, the properties of materials, or anything in the physical realm is built on atomic theory.

It has been validated in every conceivable way. Its history is deep. We knew the general nature of atoms even before quantum mechanics was developed in the early 20th century to explain its details. Without our current sophisticated understanding, modern lifestyles would be impossible.

Because theories reflect a mature level of understanding, they have great predictive power. Understanding the structure of atoms allows us to determine the shape and properties of molecules. We can fabricate materials with desirable properties only because we know how atoms interact.

In geology, no other framework has the explanatory power of the Theory of Plate Tectonics. This organizing theory embraces routine geology, aspects of life's history on Earth, and the source of the Earth's magnetic field.

What we know about the formation of continents and ocean basins comes from this overarching theory. Mountain ranges and oceanic ridges make sense within the context of motion between pieces of the Earth's crust.

It explains why the general shape of eastern South America reflects the shoreline of western Africa. Furthermore, many large geologic formations on one continent line up as if they were once continuous with formations on an adjacent continent.

Fossils of the same extinct animals are routinely found on adjacent continents. However, once the supercontinent Pangaea broke up, animal (and plant) populations became separated. Fossils left by animals subsequent to the breakup demonstrate unbroken continuity between the animal's ancestors and new lineages founded on the new land masses.

DNA exquisitely documents these same relationships. Genetic divergences of many animal and plant lineages are readily correlated with the breakup of Pangaea.

The Earth's magnetic field is produced by spinning of its solid core at the center of a hot molten mantel. Upwelling and currents in the mantel drive plate motions and give rise to earthquakes, volcanic eruptions and mid-oceanic vents.

In another realm, Big Bang Theory provides a framework for our knowledge of the origin and subsequent development of the universe. However, its true explanatory power comes from its integration of subatomic phenomena into a coherent model with cosmology.

On the largest of scales, it makes sense of the structure of galaxy clusters, galaxies, stars and exotic things like black holes. It accounts for the relativistic properties of space, light and motion and the properties of cosmic background radiation.

At the other end of the size scale, in the world's largest particle accelerators, physicists create high energy collisions between subatomic particles. The collisions replicate conditions present in the first minuscule fractions of a second of the Big Bang.

Whether scientists are focused on explanations for large or small scale phenomena, their models must not contradict one another. Big Bang Theory provides a seamless explanation for phenomena from the very smallest to the very largest.

Biology's organizing principle is the Theory of Evolution. As the famous geneticist and biologist Theodosius Dobzhansky stated, "Nothing in biology makes sense except in the light of evolution.

All living cells have important commonalities. Among the most important, they use DNA as a script for inheritance and orchestration of cell functions. This fact is no coincidence. The reason is simple, all organisms, and the cells that make them up, have a common history.

For the same reason, organisms of every kind exploit essentially the same fundamental metabolic processes. To the extent one organism's appearance or bio-chemistry differs from another's is accounted for in the history of its lineage. That history is revealed in the fossil record and corroborated by DNA comparisons.

Scientific theories are truly pinnacles of achievement. Through them we demonstrate the interconnectedness underling the universe and that its workings are discoverable. They affirm, in the words of Carl Sagan, that we do not live "in a demon haunted world."

Steve Luckstead is a medical physicist in the radiation oncology department at St. Mary Medical Center. He can be reached at


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