EHIND B TH Y E R S The Origins of Entropy O C T I E S How Culture Influences Scientific Progress N E C H E T Sadi Carnot In the late 18th and early 19 th centuries, the Industrial understand the origin of many important science ideas Revolution was well underway in England. Many new regarding heat and energy, we must revisit the Industrial types of heat engines had been invented. These new Revolution of the early 19th century. machines offered increased power and efficiency and were used to cheaply produce large amounts of goods. The arrival of new, high-pressure steam engines around With these new machines came questions about their 1800 spurred many new questions about engine nature: why did the steam engine, the water wheel, or any principles. Making use of pressures far exceeding other machinework ? Why were certain engines more atmospheric pressure, these machines increased the efficient than others? And how could machines be made power of engines. Engineers were particularly interested more efficient? in understanding the 'expansive' processes in these engines. In older engines, steam was constantly injected The desire to better understand machines often stemmed into the cylinder in order to compress the piston. In the from a fear of falling behind other nations. For instance, 'expansive' models, less steam was injected. Instead, the French engineers saw the advanced skills and steam was allowed to expand in the cylinder, thus doing technologies of the English and worried that France was the same work with less steam. The term 'work,' first falling behind in industrial know-how. The Industrial articulated in the late 18th and early 19 th centuries, Revolution brought on an obsession with increased power represented a 'quantity of action' equal to the product of and efficiency of machines. This obsession with power and force and distance. efficiency would drive investigation in science, particularly the field of thermodynamics - the study of heat and energy. Beyond 'quantity of action,' engineers were concerned with engineefficiency . The efficiency of an engine is the ! ratio of the input of heat and output of work. Without a Many people wrongly conflate science and conversion factor between heat and work, calculating technology. Science and technology are not the efficiency was difficult. Engineers instead relied on the same, but they do significantly impact one ratio between input of fuel and output of work, such as foot- another. Science seeks to understand the pounds per bushel of coal. Many who studied engine natural world, and the knowledge it creates is efficiency studied the water wheel because its efficiency often essential for technological development. was easier to quantify and conceptualize than that of the Technology, in turn, is often essential for steam engine. assisting in science research. In this historical story, notice how new technologies prompted Water wheel efficiency was calculated by observing the scientific questions. Science and technology, speed of incoming water, the size of the wheel, and the while different disciplines, are so intertwined work produced. Lazare Carnot (1753-1823) discussed thattechnoscience is sometimes used to water wheel inefficiency in his 1783 Essay on machines in describe their interaction. general. Lazare argued that the 'turbulence' and unused water motion should be minimized in order to maximize the Two ideas dominated early 19th century debates efficiency of a water wheel. While the innovations in heat concerning the nature of heat. Some natural philosophers engines were important stimuli for further research, 'older' argued that heat, or “caloric,” was a weightless fluid that technologies such as the water wheel served as models flowed between objects. Others argued in favor of the through which to discuss efficiency and work. Indeed, Sadi dynamical theory of heat, which stated that heat was Carnot (Lazare's son) would later reference the water related to particle motion. wheel in his treatise on engines,Reflexions that was published in 1824. Though such discussion of heat were important for the emerging field of thermodynamics, the scientific Despite his marginal status in the mainstream engineering investigation of heat was largely driven by engineering and practice, Sadi Carnot shared concerns about the practical industrial concerns with the efficiency of steam engines. To problems of steam engines. Carnot's concern was not with The Origins of Entropy: How Culture Influences Scientific Progress 1 www.storybehindthescience.org the resolution of whether heat was a material substance didn't optimally interact with a wheel's buckets, motion (caloric), or whether it was related to the motion of particles would be wasted and thus work output would be inefficient. that made up matter — though he sided with the first Similarly, if heat were transferred to the surroundings option. What preoccupied Carnot instead were without doing work, engine efficiency would be measurable macroscopic quantities, like pressure, compromised. temperature, heat, and work. Like other French engineers, he was concerned that France was falling behind the torrid Another key insight of Carnot's was that an engine's advance of British industry. He believed that the maximum efficiency only depends on the difference in 'haphazard' nature of improvements to heat engines was temperature between heat source and heat sink. Carnot due to the lack of systematic knowledge about the therefore determined that the engine's working substance engine's inner workings. Carnot thought that if one didn't matter at all. Whether steam, air, or some yet understood the underlying theory of steam engines, then undetermined substance, thelimits of efficiency were the one could systematically make improvements to engine same. With these understandings, Carnot imagined an work output and efficiency. Carnot's goal for the Reflexions ideal 'perfect' engine, an engine that wasreversible . By was to create a complete theory of heat engines. running the engine backwards, work could be used to Furthermore, Carnot believed this theory should rely only transfer heat from the surroundings to the heat source. on general principles and not require any reference to the Carnot used the idealized “Carnot cycle” to describe the particular substance at work in the engine. operations of a reversible engine. An ideal, reversible engine assumed no friction. The reversible engine was ! the 'limit' to an engine's productivity and efficiency. The Carnot claims that a more basic understanding reversible engine, though theoretical and not practically of the underlying principles of nature will help achievable, was the best possible engine, and thus a engineers create improvements in engine target to for which to shoot. performance. He is seeking to understand the natural world to advance technology. This kind ! of science research is referred to as applied The role of idealization in science is often research. Scientists also conduct basic or pure overlooked. In order for laws of science to be research which is undertaken solely to learn invariable relationships that apply throughout more about the natural world without concern the universe, idealization is necessary. Then, regarding whether or not that knowledge will when working with real objects, adjustments advance technology. While basic/pure research must be made taking into account how far the often draws the ire of those concerned about situation deviates from the idea. This approach potentially wasteful spending, it often creates a is at odds with common sense thinking, but it broad base of knowledge upon which other results in knowledge that can be used widely scientists can make connections they otherwise rather than having to develop different laws for could never make, and often results in the every unique situation. creation of technology that profoundly changes the world. History makes clear the importance Carnot's work was largely unheralded, possibly due to his of both basic/pure and applied scientific position between the domains of academic physics (basic research for technological advancement. science) and engineering. He also used no calculus, although Clapeyron did include calculus when he Carnot produced a number of important insights. First, reformulated Carnot's work in 1834. Carnot's ideas also while a heat source was clearly important for the operation relied on the caloric theory of heat; a position that was of the engine, the presence of acold source was just as becoming increasingly difficult to support. Part of the important. What caused the production of useful reason for the decline of the caloric theory was the work of mechanical work was the movement of heat from heat James Prescott Joule (1818-1889), an amateur source to cold sink. Carnot often used the analogy of water gentleman scientist. Joule was in favor of the dynamical wheels to explain his ideas. Because he subscribed to the theory of heat, which claimed that heat was a form of caloric theory of heat, he imagined that heat flow from hot motion. Because work could produce motion, Joule to cold sources was akin to the flowing of water through a thought that heat could be transformed into work and vice water wheel from 'high' to 'low'. Just as water was versa. 'conserved' and not consumed in the water wheel, so too was caloric conserved. Thus, one source of inefficiency Joule was the son of a Manchester brewer. Educated by was any movement of heat without the production of work. private tutors such as the famous chemist John Dalton, Again arguing by analogy, Carnot claimed that the waste Joule initially had little status in the scientific institutions of of heat was like the wasted motion of water in a water his day. Joule, supported only by his own means and wheel. If water fell without spinning a wheel, or if the water interests, was an amateur scholar with no academic 2 The Origins of Entropy: How Culture Influences Scientific Progress www.storybehindthescience.org affiliations.