Science Magazine 761 S cientific discoveries are the steps— some small, some big—on the staircase called progress, which has led to a bet- ter life for the citizens of the world. Each sci- entific discovery is made possible by the arrangement of neurons in the brain of one individual and as such is idiosyncratic. In looking back on centuries of scientific discov- eries, however, a pattern emerges which sug- gests that they fall into three categories— Charge, Challenge, and Chance—that com- bine into a “Cha-Cha-Cha” Theory of Sci- entific Discovery. (Nonscientific discoveries can be categorized similarly.) “Charge” discoveries solve problems that are quite obvious—cure heart disease, under- stand the movement of stars in the sky—but in which the way to solve the problem is not so clear. In these, the scientist is called on, as Nobel laureate Albert Szent-Györgyi put it, “to see what everyone else has seen and think what no one else has thought before.” Thus, the movement of stars in the sky and the fall of an apple from a tree were apparent to everyone, but Isaac Newton came up with the concept of gravity to explain it all in one great theory. “Challenge” discoveries are a response to an accumulation of facts or concepts that are unexplained by or incongruous with scientific theories of the time. The discoverer perceives that a new concept or a new theory is required to pull all the phenomena into one coherent whole. Sometimes the discoverer sees the anomalies and also provides the solution. Sometimes many people perceive the anom- alies, but they wait for the discoverer to pro- vide a new concept. Those individuals, whom we might call “uncoverers,” contribute greatly to science, but it is the individual who pro- poses the idea explaining all of the anomalies who deserves to be called a discoverer. “Chance” discoveries are those that are often called serendipitous and which Louis Pasteur felt favored “the prepared mind.” In this category are the instances of a chance event that the ready mind recognizes as important and then explains to other scien- tists. This category not only would include Pasteur’s discovery of optical activity (D and L isomers), but also W. C. Roentgen’s x-rays and Roy Plunkett’s Teflon. These scientists saw what no one else had seen or reported and were able to realize its importance. There are well-known examples in each one of the Cha-Cha-Cha categories (see the figure). Two conclusions are immediately apparent. The first is that the original contri- bution of the discoverer can be applied at dif- ferent points in the solution of a problem. In the Charge category, originality lies in the devising of a solution, not in the perception of the problem. In the Challenge category, the originality is in perceiving the anomalies and their importance and devising a new concept that explains them. In the Chance category, The Cha-Cha-Cha Theory of Scientific Discovery Daniel E. Koshland Jr. PHILO S O P H Y O F S C I E N C E Dividing the discovery process into three categories can aid in understanding the genesis of small, everyday advances as well as breakthroughs that appear in history books. PERSPECTIVES www.sciencemag.org SCIENCE VOL 317 10 AUGUST 2007 CATEGORIES OF DISCOVERY Problem that needed solving Movement of stars, Earth, and Sun Structure of C 6 H 6 Clear spots on petri dish Constant speed of light Preventing heart attacks Crystals of D- and -L tartaric acid Atomic spectra that could not be explained How DNA replicates and passes on coding Reagent "stuck" in storage cylinder Why offspring look like their parents Discovery Gravity Benzene structure Penicillin Special relativity Cholesterol metabolism Optical activity Quantum mechanical atom Base pairing in double helix Teflon Laws of heredity Discoverer Newton Kekulé Fleming Einstein Brown & Goldstein Pasteur Bohr Watson & Crick Plunkett Mendel Category of discovery Charge Challenge Chance Challenge Charge Chance Challenge Challenge Chance Charge C R E D IT S : N A S A ; J U P IT E R I M A G E S D. E. Koshland Jr. passed away on 23 July 2007. He was a professor of biochemistry and molecular and cell biology at the University of California, Berkeley, since 1965. He served as Science‘s editor-in-chief from 1985 to 1995. Published by AAAS o n A p ril 5 , 2 0 2 1 h ttp ://scie n ce .scie n ce m a g .o rg / D o w n lo a d e d fro m http://science.sciencemag.org/ 762 the original contribution is the perception of the importance of the accident and articulat- ing the phenomenon on which it throws light. Second, most important discoveries are usu- ally not solved in one “Eureka” moment, as movie scripts sometimes suggest. True, there are moments in which a scientist has been mulling over various facts and problems and suddenly puts them all together, but most major discoveries require scientists to make not one but a number of original discoveries and to per- sist in pursuing them until a discovery is com- plete. Thus, to solidify his theory of gravity, Newton developed calculus and laws of physics that he described in his Principia. In a modern example, Michael Brown and Joseph Goldstein not only studied the metabolism of cholesterol but also discovered the role of lipoprotein recep- tors and the movement of key proteins from the outside to the interior of cells. Great discoveries are frequently covered in textbooks with a single word or phrase, but the concepts actually become solidified as scientific understanding by a series of discoveries. It is also pertinent to define “the prepared mind” that is required for all of these inno- vations. Such a mind must be curious and knowledgeable. Curious refers to the fact that the individual is interested in phenomena and is constantly seeking to understand and explain them. Knowledgeable means that the individual has a background of facts and theo- ries as a fertile incubator into which the new facts can fall. The Cha-Cha-Cha Theory pertains to small everyday findings by scientists as well as the big discoveries that appear in history books. When, for example, a researcher dis- covers a new chemical isolated from a plant, there is so much understood today that the “charge” to that scientist is to find the for- mula and structure of the compound. There are now many ways to find the structure of an unknown chemical. Along the way there may be anomalous results that present challenges to the scientist and unexpected findings that must be interpreted by the prepared mind. So each of these represent real discoveries, not as big as a theory of gravity, but important just the same. Finally, scientific discoveries are not that different from nonscientif ic discoveries. In the earliest days, there was an obvious “charge” for a set of rules to guide conduct in the close environment of a village that led to social customs and religious guidelines such as the Ten Commandments. As more complex societies emerged, the idea of a democratic vote probably resulted from a “charge” that saw the importance of getting consensus. The Magna Carta and the Bill of Rights came out of “challenges” to an entrenched social sys- tem. So when Einstein said that scientific thinking and general thinking were not that different, he probably meant that the patterns of thought of those with “prepared minds” in government and law operated by some of the same general principles as science, even though the methods of science and law are very different. Someday we may understand the arrange- ment of neurons in the brain enough to understand how originality can arise. A wild guess would be that the brain of a discoverer has a greater tendency than the average indi- vidual to relate facts from highly separate compartments of the brain to each other. As a step to making that Herculean problem tractable, we can at least follow the traditions of scientific reductionism and use the Charge, Challenge, and Chance categories to make the interpretation of brain imaging experiments easier to analyze. 10.1126/science.1147166 N anotechnologists are increasingly interested in using mechanical vibrat- ing structures as fast, sensitive detec- tors of such properties as electric charge (1), magnetism (2), and mass (3). These devices make good detectors because, just as a bit of sealing wax changes the frequency of a tun- ing fork, the properties of a nanoresonator will change in response to external forces. Nanomechanical resonators may also be suit- able as ultracompact, high-frequency filters and mixers for electromagnetic signals (4). That is, by tailoring the vibrational properties of the structure, only select frequencies are detected. For these applications to be feasible, it is crucial that we have the ability to drive the nanomechanical resonator into motion with an electromagnetic force (i.e., “actuate” the resonator) in an efficient and controllable way. At the same time, the delicate quivering of a nanomechanical resonator as it responds to a local stimulus must be efficiently trans- duced into an electromagnetic signal that can be amplified to measurable levels. These requirements of efficiency, compactness, and speed favor methods of actuation and trans- duction that are part of the nanomechanical resonator itself. On page 780 of this issue (5), Masmanidis et al. demonstrate an intrinsic actuation met- hod ideally suited to nanoscale mechanical resonators. The method relies on a property of some crystals called piezoelectricity (6), deriving from the Greek piezen, meaning “to press.” As the name suggests, stressing such a crystal will produce a corresponding voltage between certain faces of the crystal. Con- versely, applying a voltage between the same faces will generate a corresponding mech- anical deformation or strain of the crystal. Masmanidis et al. use both singly clamped cantilevers and doubly clamped bridge res- onators (see the micrograph) that are fash- ioned from gallium arsenide (GaAs) (7). The underlying GaAs crystal orientation is chosen such that applying a voltage between the top and bottom faces will cause it to either elon- gate or shorten, depending on the polarity of the applied electric field. To understand better how the motion is produced, consider a GaAs cantilever and suppose that an ac voltage source is applied between its top and bottom faces. If the fre- quency of the ac voltage matches that of one of the cantilever’s longitudinal vibration modes (i.e., stretching modes along the direc- tion of the cantilever), then the cantilever will ring at this frequency. However, longitudinal modes are difficult to detect because of their relatively high frequencies and small dis- placement amplitudes. As with stringed musi- cal instruments, it is preferable to excite the lower frequency, bending modes of the can- tilever, especially the fundamental mode. The method of actuation should also be internal to the cantilever and not require external elec- trodes attached to its top and bottom faces. Masmanidis et al. elegantly meet both of A method for vibrating a nanocantilever may yield much more sensitive measurement tools and computers based on mechanical logic devices. How to Strum a Nanobar Miles Blencowe APPLIED PHYSICS The author is in the Department of Physics and Astronomy, Dartmouth College, Hanover, NH 03755, USA. E-mail: blencowe@dartmouth.edu 10 AUGUST 2007 VOL 317 SCIENCE www.sciencemag.org PERSPECTIVES Published by AAAS o n A p ril 5 , 2 0 2 1 h ttp ://scie n ce .scie n ce m a g .o rg / D o w n lo a d e d fro m http://science.sciencemag.org/ The Cha-Cha-Cha Theory of Scientific Discovery Daniel E. Koshland Jr. DOI: 10.1126/science.1147166 (5839), 761-762.317Science ARTICLE TOOLS http://science.sciencemag.org/content/317/5839/761 CONTENT RELATED http://science.sciencemag.org/content/sci/317/5839/721.full PERMISSIONS http://www.sciencemag.org/help/reprints-and-permissions Terms of ServiceUse of this article is subject to the is a registered trademark of AAAS.ScienceScience, 1200 New York Avenue NW, Washington, DC 20005. 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