In Praise of Hard Questions - by Tom Siegfried

Great cases, as U.S. Supreme Court Justice Oliver Wendell Holmes suggested acentury ago, may make bad law. But great questions often make very goodscience.

Unsolved mysteries provide science with motivation and direction. Gaps inthe road to scientific knowledge are not potholes to be avoided, butopportunities to be exploited.

"Fundamental questions are guideposts; they stimulate people,"says 2004 Nobel physics laureate David Gross. "One of the most creativequalities a research scientist can have is the ability to ask the rightquestions."

Science's greatest advances occur on the frontiers, at the interface betweenignorance and knowledge, where the most profound questions are posed. There'sno better way to assess the current condition of science than listing thequestions that science cannot answer. "Science," Gross declares,"is shaped by ignorance."

There have been times, though, when some believed that science had pavedover all the gaps, ending the age of ignorance. When Science was born,in 1880, James Clerk Maxwell had died just the year before, after successfullyexplaining light, electricity, magnetism, and heat. Along with gravity, whichNewton had mastered 2 centuries earlier, physics was, to myopic eyes,essentially finished. Darwin, meanwhile, had established the guiding principleof biology, and Mendeleyev's periodic table--only a decade old--allowedchemistry to publish its foundations on a poster board. Maxwell himselfmentioned that many physicists believed the trend in their field was merely tomeasure the values of physical constants "to another place ofdecimals."

Nevertheless, great questions raged. Savants of science debated not only thepower of natural selection, but also the origin of the solar system, the ageand internal structure of Earth, and the prospect of a plurality of worldspopulating the cosmos.

In fact, at the time of Maxwell's death, his theory of electromagneticfields was not yet widely accepted or even well known; experts still arguedabout whether electricity and magnetism propagated their effects via"action at a distance," as gravity (supposedly) did, or by MichaelFaraday's "lines of force" (incorporated by Maxwell into his fields).Lurking behind that dispute was the deeper issue of whether gravity could beunified with electromagnetism (Maxwell thought not), a question that remainsone of the greatest in science today, in a somewhat more complicated form.

Maxwell knew full well that his accomplishments left questions unanswered.His calculations regarding the internal motion of molecules did not agree withmeasurements of specific heats, for instance. "Something essential to thecomplete state of the physical theory of molecular encounters must havehitherto escaped us," he commented.

When Science turned 20--at the 19th century's end--Maxwell's mentorWilliam Thomson (Lord Kelvin) articulated the two grand gaps in knowledge ofthe day. (He called them "clouds" hanging over physicists' heads.)One was the mystery of specific heats that Maxwell had identified; the otherwas the failure to detect the ether, a medium seemingly required by Maxwell'selectromagnetic waves.

Filling those two gaps in knowledge required the 20th century's quantum andrelativity revolutions. The ignorance enveloped in Kelvin's clouds was theimpetus for science's revitalization.

Throughout the last century, pursuing answers to great questions reshapedhuman understanding of the physical and living world. Debates over theplurality of worlds assumed galactic proportions, specifically addressingwhether Earth's home galaxy, the Milky Way, was only one of many suchconglomerations of stars. That issue was soon resolved in favor of the MilkyWay's nonexclusive status, in much the same manner that Earth itself had beendemoted from its central role in the cosmos by Copernicus centuries before.

But the existence of galaxies outside our own posed another question, aboutthe apparent motions of those galaxies away from one another. That issue echoeda curious report in Science's first issue about a set of stars forminga triangular pattern, with a double star at the apex and two others forming thebase. Precise observations showed the stars to be moving apart, making thetriangle bigger but maintaining its form.

"It seems probable that all these stars are slowly moving away from onecommon point, so that many years back they were all very much closer to oneanother," Science reported, as though the four stars had allbegun their journey from the same place. Understanding such motion was aquestion "of the highest interest."

A half a century later, Edwin Hubble enlarged that question from one aboutstellar motion to the origin and history of the universe itself. He showed thatgalaxies also appeared to be receding from a common starting point, evidencethat the universe was expanding. With Hubble's discovery, cosmology's grandquestions began to morph from the philosophical to the empirical. And with thediscovery of the cosmic microwave background in the 1960s, the big bang theoryof the universe's birth assumed the starring role on the cosmologicalstage--providing cosmologists with one big answer and many new questions.

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By Science's centennial, a quarter-century ago,many gaps still remained in knowledge of the cosmos; some of them have sincebeen filled, while others linger. At that time debate continued over theexistence of planets around faraway stars, a question now settled with thediscovery of dozens of planets in the solar system's galactic neighborhood. Butnow a bigger question looms beyond the scope of planets or even galaxies: theprospect of multiple universes, cousins to the bubble of time and space thathumans occupy.

And not only may the human universe not be alone (defying the old definitionof universe), humans may not be alone in their own space, either. The possibleexistence of life elsewhere in the cosmos remains as great a gap as any inpresent-day knowledge. And it is enmeshed with the equally deep mystery oflife's origin on Earth.

Life, of course, inspires many deep questions, from the prospects forimmortality to the prognosis for eliminating disease. Scientists continue towonder whether they will ever be able to create new life forms from scratch, orat least simulate life's self-assembling capabilities. Biologists, physicists,mathematicians, and computer scientists have begun cooperating on asophisticated "systems biology" aimed at understanding how thecountless molecular interactions at the heart of life fit together in theworkings of cells, organs, and whole animals. And if successful, the systems approachshould help doctors tailor treatments to individual variations in DNA,permitting personalized medicine that deters disease without inflicting sideeffects. Before Science turns 150, revamped versions of modernmedicine may make it possible for humans to live that long, too.

As Science and science age, knowledge and ignorance have coevolved,and the nature of the great questions sometimes changes. Old questions aboutthe age and structure of the Earth, for instance, have given way to issuesconcerning the planet's capacity to support a growing and aging population.

Some great questions get bigger over time, encompassing an ever-expandinguniverse, or become more profound, such as the quest to understandconsciousness. On the other hand, many deep questions drive science to smallerscales, more minute than the realm of atoms and molecules, or to a greaterdepth of detail underlying broad-brush answers to past big questions. In 1880,some scientists remained unconvinced by Maxwell's evidence for atoms. Today,the analogous debate focuses on superstrings as the ultimate bits of matter, ona scale a trillion trillion times smaller. Old arguments over evolution andnatural selection have descended to debates on the dynamics of speciation, orhow particular behaviors, such as altruistic cooperation, have emerged from thelaws of individual competition.

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Great questions themselves evolve, of course, because theiranswers spawn new and better questions in turn. The solutions to Kelvin'sclouds--relativity and quantum physics--generated many of the mysteries ontoday's list, from the composition of the cosmos to the prospect for quantumcomputers.

Ultimately, great questions like these both define the state of scientificknowledge and drive the engines of scientific discovery. Where ignorance andknowledge converge, where the known confronts the unknown, is where scientificprogress is most dramatically made. "Thoroughly conscious ignorance,"wrote Maxwell, "is the prelude to every real advance in science."

So when science runs out of questions, it would seem, science will come toan end. But there's no real danger of that. The highway from ignorance toknowledge runs both ways: As knowledge accumulates, diminishing the ignoranceof the past, new questions arise, expanding the areas of ignorance to explore.

Maxwell knew that even an era of precision measurements is not a sign ofscience's end but preparation for the opening of new frontiers. In every branchof science, Maxwell declared, "the labor of careful measurement has beenrewarded by the discovery of new fields of research and by the development ofnew scientific ideas."

If science's progress seems to slow, it's because its questions getincreasingly difficult, not because there will be no new questions left toanswer.

Fortunately, hard questions also can make great science, just as JusticeHolmes noted that hard cases, like great cases, made bad law. Bad law resulted,he said, because emotional concerns about celebrated cases exerted pressuresthat distorted well-established legal principles. And that's why the situation inscience is the opposite of that in law. The pressures of the great, hardquestions bend and even break well-established principles, which is what makesscience forever self-renewing--and which is what demolishes the nonsensicalnotion that science's job will ever be done.