Should scientists think harder about explaining the concept “theory”?

For more than half a century, emeritus professor Charles W. Misner of the University of Maryland Gravitation Theory Group has observed and participated in public discussions of science. He believes that scientists need to speak more clearly to journalists and the public about scientific theories. Recent public-trust-in-science postings in this venue caused him to speak up. This is a report on his views.

It’s important first to convey a sense of who he is. Misner’s honors include most recently the Albert Einstein Medal . He has held visiting faculty positions at Princeton University; the Max Planck Institute for Gravitational Physics in Potsdam, Germany; the University of California, Santa Barbara; Oxford University; Caltech; and Cambridge University. The New York Times once called the late Princeton physicist John Archibald Wheeler a “visionary ... who helped invent the theory of nuclear fission, gave black holes their name and argued about the nature of reality with Albert Einstein and Niels Bohr.” The Times cited five of Wheeler’s 51 PhD students, including not only Nobel laureate Richard Feynman but Kip Thorne and Misner. The 1215-page graduate physics textbook Gravitation , in print since 1973, is regularly called MTW for the initials of its authors: Misner, Thorne, and Wheeler.

Recognizing the importance of framing in any communication effort, Misner believes it’s vital for scientists to find language for clearly distinguishing what he sees as three categories of theory. An important part of science’s overall communication challenge, he assumes, is the perennial problem of public misunderstanding of the word theory itself. Too often people see a theory as merely a guess or educated guess or hypothesis, rather than as systematized understanding with explanatory power.

And recognizing the difficulty of finding the mot juste in this framing task—in this effort to orient the reader or listener solidly from the outset—Misner freely admits to struggling. In particular he seeks the right name for what he sees as the most important category of theory: one “whose validity has been certified by better theories, and whose domain of usefulness is limited by known failures where those better theories are needed, but which continues in use as more insightful than its more complicated replacements.”

In a presentation, he listed examples:

• • Pre-Ptolemaic motion of celestial objects through the heavens
• • Kepler’s laws
• • Newtonian mechanics
• • Heisenberg–Schrödinger quantum mechanics
• • Maxwell–Lorentz classical electrodynamics
• • Schwinger-Feynman-Dyson electrodynamics

He focuses in particular on the example of Newtonian mechanics, observing that it has limitations—it has been falsified—in the realms of special relativity, quantum mechanics, Einstein gravity, and unforeseen sensitivity to initial conditions. Nevertheless, Misner says that unlike a completely false theory such as early chemists’ belief in the “phlogiston” then thought to underlie combustion, Newtonian mechanics retains widespread, important applicability in macroscopic contexts for scientists and engineers.

What to call such “everyday theories which are immune from worry about falsification by a future experiment since they’ve already been falsified”? He considered the name “archival theories.” The name “core theories,” he says, sounds “a bit too weak.” For the moment he has tentatively settled on “certified theories,” echoing the part about certification in the definition cited above. That definition comprises four criteria, he says, one of which is “certified by better theories as correct and reliable (within known limits).”

Misner sees scientific knowledge as structured by this first core set of certified theories plus a second and a third category. As a scientist always looking for better ways to get ideas across, he describes the second and third using a geophysical metaphor that connotes ascending order. Second, he says, is the “active atmosphere of cutting edge theories, the best we know in any given area.” Third is the “stratosphere of speculative theories, representing plausible directions toward better theories.”

He stipulates that the domain of his thinking is sciences having “clearly defined theories, such as physics, chemistry, genetics.” And he believes that the many certified theories “are defined by their relationships to other theories,” such that “we need to study relationships between theories.” This occurs, he says, “within a wide-ranging survey of what scientific knowledge can mean.”

For recognizing certified theories via such study and surveying, Misner describes three kinds of relationship that theories might have with each other. He sees “emergent laws and concepts” among this collection. Another kind of relationship is “correspondence principles,” for which he offers examples:

• • Quantum theory gives classical mechanics when quantum numbers are large
• • General relativity reduces to special relativity when curvature is negligible
• • General relativity reduces to Newtonian gravity for weak fields and slow motions
• • Special relativity gives Newtonian mechanics for slow motions
• • Electroweak Yang–Mills gives quantum electrodynamics at low energies

He adds the category “evanescent laws,” explaining that a “law or property can be called evanescent when in some domain” it “becomes irrelevant or useless,” or “it is indefinable or misleading,” or “its normal consequences can be evaded,” or “it (rarely) is incorrect.” Again he gives examples:

• • Conservation of quantum chromodynamics color charge as one moves into atomic physics
• • Coulomb’s law as one calculates the motions of solar system planets
• • Schrödinger equation in molecular genetics
• • Energy on cosmological scales
• • Entropy in large self-gravitating systems

With his characteristic attention not just to physics but to the language used to talk about science—and again drawing on a physics metaphor—Misner recounts the origin of the name evanescent laws: “In the ray optics limit of optical wave theory, one meets total internal reflection using Snell’s law. If this is analyzed using wave optics, one finds that beyond the reflection interface there is an ‘evanescent wave’ which disappears exponentially beyond the interface.” He sums up, “Some physics laws also disappear beyond applicable boundaries.”

Some of the potential for clearer public understanding of science also disappears beyond applicable—but in Misner’s mind unnecessary—language boundaries. Misner emphasizes that he presents a viewpoint that, while “provided as background for scientists talking to journalists and politicians,” is " too technical for direct delivery to a nonscientific public.” But he wants to push those language boundaries back, and hopes to see fellow scientists pushing too.

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Steven T. Corneliussen, a media analyst for the American Institute of Physics, monitors three national newspapers, the weeklies Nature and Science, and occasionally other publications. He has published op-eds in the Washington Post and other newspapers, has written for NASA’s history program, and is a science writer at a particle-accelerator laboratory.