Misplaced Pages

#255744

115-494: A thought experiment is a hypothetical situation in which a hypothesis , theory , or principle is laid out for the purpose of thinking through its consequences. The concept is also referred to using the German-language term Gedankenexperiment within the work of the physicist Ernst Mach and includes thoughts about what may have occurred if a different course of action were taken. The importance of this ability

230-403: A closed system in terms of work and heat . It can be linked to the law of conservation of energy . Conceptually, the first law describes the fundamental principle that systems do not consume or 'use up' energy, that energy is neither created nor destroyed, but is simply converted from one form to another. The second law is concerned with the direction of natural processes. It asserts that

345-612: A "contrary-to-fact conditional" – speculate on the possible outcomes of a different past; and ask "What might have happened if A had happened instead of B?" (e.g., "If Isaac Newton and Gottfried Leibniz had cooperated with each other, what would mathematics look like today?"). The study of counterfactual speculation has increasingly engaged the interest of scholars in a wide range of domains such as philosophy, psychology, cognitive psychology, history, political science, economics, social psychology, law, organizational theory, marketing, and epidemiology. Semifactual thought experiments –

460-424: A colder to a warmer body without some other change, connected therewith, occurring at the same time. The second law of thermodynamics allows the definition of the concept of thermodynamic temperature , but this has been formally delegated to the zeroth law of thermodynamics . The first law of thermodynamics provides the definition of the internal energy of a thermodynamic system , and expresses its change for

575-418: A crystallized structure of reduced disorder (sticking together in a certain order due to molecular attraction). The entropy of the system decreases, but the system approaches uniformity with its surroundings (category III). On the other hand, consider the refrigeration of water in a warm environment. Due to refrigeration, as heat is extracted from the water, the temperature and entropy of the water decreases, as

690-412: A factory. The robotic machinery requires electrical work input and instructions, but when completed, the manufactured products have less uniformity with their surroundings, or more complexity (higher order) relative to the raw materials they were made from. Thus, system entropy or disorder decreases while the tendency towards uniformity between the system and its environment is counteracted. In this example,

805-420: A forecast model after an event has happened in order to test whether the model's simulation is valid. The activity of retrodiction (or postdiction ) involves moving backward in time, step-by-step, in as many stages as are considered necessary, from the present into the speculated past to establish the ultimate cause of a specific event (e.g., reverse engineering and forensics ). Given that retrodiction

920-464: A full statement of the second law: Differing from Planck's just foregoing principle, this one is explicitly in terms of entropy change. Removal of matter from a system can also decrease its entropy. The second law has been shown to be equivalent to the internal energy U defined as a convex function of the other extensive properties of the system. That is, when a system is described by stating its internal energy U , an extensive variable, as

1035-520: A function of its entropy S , volume V , and mol number N , i.e. U = U ( S , V , N ), then the temperature is equal to the partial derivative of the internal energy with respect to the entropy (essentially equivalent to the first TdS equation for V and N held constant): The Clausius inequality, as well as some other statements of the second law, must be re-stated to have general applicability for all forms of heat transfer, i.e. scenarios involving radiative fluxes. For example,

1150-429: A heat engine operating between any two given thermal or heat reservoirs at different temperatures. Carnot's principle was recognized by Carnot at a time when the caloric theory represented the dominant understanding of the nature of heat, before the recognition of the first law of thermodynamics , and before the mathematical expression of the concept of entropy. Interpreted in the light of the first law, Carnot's analysis

1265-422: A hypothesis. In common usage in the 21st century, a hypothesis refers to a provisional idea whose merit requires evaluation. For proper evaluation, the framer of a hypothesis needs to define specifics in operational terms. A hypothesis requires more work by the researcher in order to either confirm or disprove it. In due course, a confirmed hypothesis may become part of a theory or occasionally may grow to become

SECTION 10

#1732765935256

1380-445: A light beam, leading to special relativity . This is a unique use of a scientific thought experiment, in that it was never carried out, but led to a successful theory, proven by other empirical means. Further categorization of thought experiments can be attributed to specific properties. In many thought experiments, the scenario would be nomologically possible , or possible according to the laws of nature. John Searle's Chinese room

1495-461: A method used by mathematicians, that of "investigating from a hypothesis". In this sense, 'hypothesis' refers to a clever idea or to a convenient mathematical approach that simplifies cumbersome calculations . Cardinal Bellarmine gave a famous example of this usage in the warning issued to Galileo in the early 17th century: that he must not treat the motion of the Earth as a reality, but merely as

1610-406: A natural process runs only in one sense, and is not reversible. That is, the state of a natural system itself can be reversed, but not without increasing the entropy of the system's surroundings, that is, both the state of the system plus the state of its surroundings cannot be together, fully reversed, without implying the destruction of entropy. For example, when a path for conduction or radiation

1725-557: A number of important statistical tests which are used to test the hypotheses. Mount Hypothesis in Antarctica is named in appreciation of the role of hypothesis in scientific research. Several hypotheses have been put forth, in different subject areas: hypothesis [...]— Working hypothesis , a hypothesis suggested or supported in some measure by features of observed facts, from which consequences may be deduced which can be tested by experiment and special observations, and which it

1840-593: A nutshell, the Clausius inequality is saying that when a cycle is completed, the change in the state property S will be zero, so the entropy that was produced during the cycle must have transferred out of the system by heat transfer. The δ \delta (or đ) indicates a path dependent integration. Due to the inherent emission of radiation from all matter, most entropy flux calculations involve incident, reflected and emitted radiative fluxes. The energy and entropy of unpolarized blackbody thermal radiation,

1955-460: A particular characteristic. In entrepreneurial setting, a hypothesis is used to formulate provisional ideas about the attributes of products or business models. The formulated hypothesis is then evaluated, where the hypothesis is proven to be either "true" or "false" through a verifiability - or falsifiability -oriented experiment . Any useful hypothesis will enable predictions by reasoning (including deductive reasoning ). It might predict

2070-436: A particular future end-point to the present to determine what policy measures would be required to reach that future. According to Jansen (1994, p. 503: Within the framework of technological development, "forecasting" concerns the extrapolation of developments towards the future and the exploration of achievements that can be realized through technology in the long term. Conversely, the reasoning behind "backcasting" is: on

2185-745: A patterned way of thinking that is designed to allow us to explain, predict, and control events in a better and more productive way. In terms of their theoretical consequences, thought experiments generally: Thought experiments can produce some very important and different outlooks on previously unknown or unaccepted theories. However, they may make those theories themselves irrelevant, and could possibly create new problems that are just as difficult, or possibly more difficult to resolve. In terms of their practical application, thought experiments are generally created to: Generally speaking, there are seven types of thought experiments in which one reasons from causes to effects, or effects to causes: Prefactual (before

2300-460: A perpetual motion machine had tried to circumvent the restrictions of first law of thermodynamics by extracting the massive internal energy of the environment as the power of the machine. Such a machine is called a "perpetual motion machine of the second kind". The second law declared the impossibility of such machines. Carnot's theorem (1824) is a principle that limits the maximum efficiency for any possible engine. The efficiency solely depends on

2415-438: A problem is commonly referred to as a hypothesis—or, often, as an " educated guess " —because it provides a suggested outcome based on the evidence. However, some scientists reject the term "educated guess" as incorrect. Experimenters may test and reject several hypotheses before solving the problem. According to Schick and Vaughn, researchers weighing up alternative hypotheses may take into consideration: A working hypothesis

SECTION 20

#1732765935256

2530-644: A purely mathematical axiomatic foundation. His statement of the second law is known as the Principle of Carathéodory, which may be formulated as follows: In every neighborhood of any state S of an adiabatically enclosed system there are states inaccessible from S. With this formulation, he described the concept of adiabatic accessibility for the first time and provided the foundation for a new subfield of classical thermodynamics, often called geometrical thermodynamics . It follows from Carathéodory's principle that quantity of energy quasi-statically transferred as heat

2645-567: A social or political organization. The use of the state of nature to imagine the origins of government, as by Thomas Hobbes and John Locke , may also be considered a thought experiment. Søren Kierkegaard explored the possible ethical and religious implications of Abraham 's binding of Isaac in Fear and Trembling . Similarly, Friedrich Nietzsche , in On the Genealogy of Morals , speculated about

2760-467: A synthesis. Concepts in Hempel's deductive-nomological model play a key role in the development and testing of hypotheses. Most formal hypotheses connect concepts by specifying the expected relationships between propositions . When a set of hypotheses are grouped together, they become a type of conceptual framework . When a conceptual framework is complex and incorporates causality or explanation, it

2875-402: A theory itself. Normally, scientific hypotheses have the form of a mathematical model . Sometimes, but not always, one can also formulate them as existential statements , stating that some particular instance of the phenomenon under examination has some characteristic and causal explanations, which have the general form of universal statements , stating that every instance of the phenomenon has

2990-415: A thought experiment is to explore the potential consequences of the principle in question: Given the structure of the experiment, it may not be possible to perform it; and, even if it could be performed, there need not be an intention to perform it. Examples of thought experiments include Schrödinger's cat , illustrating quantum indeterminacy through the manipulation of a perfectly sealed environment and

3105-611: A tiny bit of radioactive substance, and Maxwell's demon , which attempts to demonstrate the ability of a hypothetical finite being to violate the 2nd law of thermodynamics . It is a common element of science-fiction stories. Thought experiments, which are well-structured, well-defined hypothetical questions that employ subjunctive reasoning ( irrealis moods ) – "What might happen (or, what might have happened) if . . . " – have been used to pose questions in philosophy at least since Greek antiquity, some pre-dating Socrates . In physics and other sciences many thought experiments date from

3220-450: A useful guide to address problems that are still in a formative phase. In recent years, philosophers of science have tried to integrate the various approaches to evaluating hypotheses, and the scientific method in general, to form a more complete system that integrates the individual concerns of each approach. Notably, Imre Lakatos and Paul Feyerabend , Karl Popper's colleague and student, respectively, have produced novel attempts at such

3335-410: A very long time for both scientists and philosophers. The irrealis moods are ways to categorize it or to speak about it. This helps explain the extremely wide and diverse range of the application of the term thought experiment once it had been introduced into English. Galileo's demonstration that falling objects must fall at the same rate regardless of their masses was a significant step forward in

3450-399: Is nomologically possible. Some thought experiments present scenarios that are not nomologically possible. In his Twin Earth thought experiment , Hilary Putnam asks us to imagine a scenario in which there is a substance with all of the observable properties of water (e.g., taste, color, boiling point), but is chemically different from water. It has been argued that this thought experiment

3565-466: Is a function of state , while heat, like work, is not. For an actually possible infinitesimal process without exchange of mass with the surroundings, the second law requires that the increment in system entropy fulfills the inequality This is because a general process for this case (no mass exchange between the system and its surroundings) may include work being done on the system by its surroundings, which can have frictional or viscous effects inside

Thought experiment - Misplaced Pages Continue

3680-568: Is a holonomic process function , in other words, δ Q = T d S {\displaystyle \delta Q=TdS} . Though it is almost customary in textbooks to say that Carathéodory's principle expresses the second law and to treat it as equivalent to the Clausius or to the Kelvin-Planck statements, such is not the case. To get all the content of the second law, Carathéodory's principle needs to be supplemented by Planck's principle, that isochoric work always increases

3795-566: Is a hypothesis that is provisionally accepted as a basis for further research in the hope that a tenable theory will be produced, even if the hypothesis ultimately fails. Like all hypotheses, a working hypothesis is constructed as a statement of expectations, which can be linked to the exploratory research purpose in empirical investigation. Working hypotheses are often used as a conceptual framework in qualitative research. The provisional nature of working hypotheses makes them useful as an organizing device in applied research. Here they act like

3910-429: Is a monotonic function of the internal energy. Nevertheless, this principle of Planck is not actually Planck's preferred statement of the second law, which is quoted above, in a previous sub-section of the present section of this present article, and relies on the concept of entropy. A statement that in a sense is complementary to Planck's principle is made by Claus Borgnakke and Richard E. Sonntag. They do not offer it as

4025-409: Is a process in which "past observations, events, add and data are used as evidence to infer the process(es) that produced them" and that diagnosis "involve[s] going from visible effects such as symptoms, signs and the like to their prior causes", the essential balance between prediction and retrodiction could be characterized as: regardless of whether the prognosis is of the course of the disease in

4140-508: Is almost customary in textbooks to speak of the "Kelvin–Planck statement" of the law, as for example in the text by ter Haar and Wergeland . This version, also known as the heat engine statement , of the second law states that Max Planck stated the second law as follows. Rather like Planck's statement is that of George Uhlenbeck and G. W. Ford for irreversible phenomena . Constantin Carathéodory formulated thermodynamics on

4255-486: Is an ideal search toward determining the nature and scope of the technological challenge posed by sustainable development, and it can thus serve to direct the search process toward new – sustainable – technology. Thought experiments have been used in a variety of fields, including philosophy, law, physics , and mathematics. In philosophy they have been used at least since classical antiquity , some pre-dating Socrates . In law, they were well known to Roman lawyers quoted in

4370-1320: Is calculated using the spectral energy and entropy radiance expressions derived by Max Planck using equilibrium statistical mechanics, K ν = 2 h c 2 ν 3 exp ⁡ ( h ν k T ) − 1 , {\displaystyle K_{\nu }={\frac {2h}{c^{2}}}{\frac {\nu ^{3}}{\exp \left({\frac {h\nu }{kT}}\right)-1}},} L ν = 2 k ν 2 c 2 ( ( 1 + c 2 K ν 2 h ν 3 ) ln ⁡ ( 1 + c 2 K ν 2 h ν 3 ) − ( c 2 K ν 2 h ν 3 ) ln ⁡ ( c 2 K ν 2 h ν 3 ) ) {\displaystyle L_{\nu }={\frac {2k\nu ^{2}}{c^{2}}}((1+{\frac {c^{2}K_{\nu }}{2h\nu ^{3}}})\ln(1+{\frac {c^{2}K_{\nu }}{2h\nu ^{3}}})-({\frac {c^{2}K_{\nu }}{2h\nu ^{3}}})\ln({\frac {c^{2}K_{\nu }}{2h\nu ^{3}}}))} where c

4485-402: Is clear that on uniting the two, the more rapid one will be partly retarded by the slower, and the slower will be somewhat hastened by the swifter. Do you not agree with me in this opinion? Simplicio . You are unquestionably right. Salviati . But if this is true, and if a large stone moves with a speed of, say, eight while a smaller moves with a speed of four, then when they are united,

4600-506: Is fully converted to work) in a cyclic fashion without any other result. Now pair it with a reversed Carnot engine as shown by the right figure. The efficiency of a normal heat engine is η and so the efficiency of the reversed heat engine is 1/ η . The net and sole effect of the combined pair of engines is to transfer heat Δ Q = Q ( 1 η − 1 ) {\textstyle \Delta Q=Q\left({\frac {1}{\eta }}-1\right)} from

4715-457: Is generally referred to as a theory. According to noted philosopher of science Carl Gustav Hempel , Hempel provides a useful metaphor that describes the relationship between a conceptual framework and the framework as it is observed and perhaps tested (interpreted framework). "The whole system floats, as it were, above the plane of observation and is anchored to it by rules of interpretation. These might be viewed as strings which are not part of

Thought experiment - Misplaced Pages Continue

4830-550: Is known as the Clausius statement : Heat can never pass from a colder to a warmer body without some other change, connected therewith, occurring at the same time. The statement by Clausius uses the concept of 'passage of heat'. As is usual in thermodynamic discussions, this means 'net transfer of energy as heat', and does not refer to contributory transfers one way and the other. Heat cannot spontaneously flow from cold regions to hot regions without external work being performed on

4945-495: Is made available, heat always flows spontaneously from a hotter to a colder body. Such phenomena are accounted for in terms of entropy change . A heat pump can reverse this heat flow, but the reversal process and the original process, both cause entropy production, thereby increasing the entropy of the system's surroundings. If an isolated system containing distinct subsystems is held initially in internal thermodynamic equilibrium by internal partitioning by impermeable walls between

5060-567: Is not nomologically possible, although it may be possible in some other sense, such as metaphysical possibility . It is debatable whether the nomological impossibility of a thought experiment renders intuitions about it moot. Hypothesis A hypothesis ( pl. : hypotheses ) is a proposed explanation for a phenomenon . For a hypothesis to be a scientific hypothesis , the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with

5175-478: Is physically equivalent to the second law of thermodynamics, and remains valid today. Some samples from his book are: In modern terms, Carnot's principle may be stated more precisely: The German scientist Rudolf Clausius laid the foundation for the second law of thermodynamics in 1850 by examining the relation between heat transfer and work. His formulation of the second law, which was published in German in 1854,

5290-400: Is proposed to subject to an extended course of such investigation, with the hope that, even should the hypothesis thus be overthrown, such research may lead to a tenable theory. Second law of thermodynamics The second law of thermodynamics establishes the concept of entropy as a physical property of a thermodynamic system . It predicts whether processes are forbidden despite obeying

5405-626: Is taken separately from that due to heat transfer by conduction and convection ( δ Q C C \delta Q_{CC} ), where the temperature is evaluated at the system boundary where the heat transfer occurs. The modified Clausius inequality, for all heat transfer scenarios, can then be expressed as, ∫ cycle ( δ Q C C T b + δ S NetRad ) ≤ 0 {\displaystyle \int _{\text{cycle}}({\frac {\delta Q_{CC}}{T_{b}}}+\delta S_{\text{NetRad}})\leq 0} In

5520-478: Is that it allows the experimenter to imagine what may occur in the future, as well as the implications of alternate courses of action. The ancient Greek δείκνυμι , deiknymi , 'thought experiment', "was the most ancient pattern of mathematical proof ", and existed before Euclidean mathematics , where the emphasis was on the conceptual, rather than on the experimental part of a thought experiment. Johann Witt-Hansen established that Hans Christian Ørsted

5635-517: Is the speed of light, k is the Boltzmann constant, h is the Planck constant, ν is frequency, and the quantities K v and L v are the energy and entropy fluxes per unit frequency, area, and solid angle. In deriving this blackbody spectral entropy radiance, with the goal of deriving the blackbody energy formula, Planck postulated that the energy of a photon was quantized (partly to simplify

5750-542: The Digest . In physics and other sciences, notable thought experiments date from the 19th and, especially, the 20th century; but examples can be found at least as early as Galileo . In philosophy, a thought experiment typically presents an imagined scenario with the intention of eliciting an intuitive or reasoned response about the way things are in the thought experiment. (Philosophers might also supplement their thought experiments with theoretical reasoning designed to support

5865-423: The antecedent of a proposition ; thus in the proposition "If P , then Q ", P denotes the hypothesis (or antecedent); Q can be called a consequent . P is the assumption in a (possibly counterfactual ) What If question. The adjective hypothetical , meaning "having the nature of a hypothesis", or "being assumed to exist as an immediate consequence of a hypothesis", can refer to any of these meanings of

SECTION 50

#1732765935256

5980-675: The substantiality of the soul . Scientists tend to use thought experiments as imaginary, "proxy" experiments prior to a real, "physical" experiment ( Ernst Mach always argued that these gedankenexperiments were "a necessary precondition for physical experiment"). In these cases, the result of the "proxy" experiment will often be so clear that there will be no need to conduct a physical experiment at all. Scientists also use thought experiments when particular physical experiments are impossible to conduct ( Carl Gustav Hempel labeled these sorts of experiment " theoretical experiments-in-imagination "), such as Einstein's thought experiment of chasing

6095-441: The 19th and especially the 20th Century, but examples can be found at least as early as Galileo . In thought experiments, we gain new information by rearranging or reorganizing already known empirical data in a new way and drawing new (a priori) inferences from them, or by looking at these data from a different and unusual perspective. In Galileo's thought experiment, for example, the rearrangement of empirical experience consists of

6210-455: The Clausius statement implies the Kelvin statement. We can prove in a similar manner that the Kelvin statement implies the Clausius statement, and hence the two are equivalent. Planck offered the following proposition as derived directly from experience. This is sometimes regarded as his statement of the second law, but he regarded it as a starting point for the derivation of the second law. It

6325-438: The absence of treatment, or of the application of a specific treatment regimen to a specific disorder in a particular patient. The activity of backcasting – the term backcasting was coined by John Robinson in 1982 – involves establishing the description of a very definite and very specific future situation. It then involves an imaginary moving backward in time, step-by-step, in as many stages as are considered necessary, from

6440-438: The absolute entropy of pure substances from measured heat capacity curves and entropy changes at phase transitions, i.e. by calorimetry. Introducing a set of internal variables ξ {\displaystyle \xi } to describe the deviation of a thermodynamic system from a chemical equilibrium state in physical equilibrium (with the required well-defined uniform pressure P and temperature T ), one can record

6555-406: The alternative hypothesis. The alternative hypothesis, as the name suggests, is the alternative to the null hypothesis: it states that there is some kind of relation. The alternative hypothesis may take several forms, depending on the nature of the hypothesized relation; in particular, it can be two-sided (for example: there is some effect, in a yet unknown direction) or one-sided (the direction of

6670-421: The available scientific theories. Even though the words "hypothesis" and " theory " are often used interchangeably, a scientific hypothesis is not the same as a scientific theory . A working hypothesis is a provisionally accepted hypothesis proposed for further research in a process beginning with an educated guess or thought. A different meaning of the term hypothesis is used in formal logic , to denote

6785-448: The basis of an interconnecting picture of demands technology must meet in the future – "sustainability criteria" – to direct and determine the process that technology development must take and possibly also the pace at which this development process must take effect. Backcasting [is] both an important aid in determining the direction technology development must take and in specifying the targets to be set for this purpose. As such, backcasting

6900-482: The benefit of others. Here, the relevant question is not whether the action is moral or not, but more broadly whether a moral theory is correct that says morality is determined solely by an action's consequences (See Consequentialism ). John Searle imagines a man in a locked room who receives written sentences in Chinese, and returns written sentences in Chinese, according to a sophisticated instruction manual. Here,

7015-407: The circumstances of the present into the future. According to David Sarewitz and Roger Pielke (1999, p123), scientific prediction takes two forms: Although they perform different social and scientific functions, the only difference between the qualitatively identical activities of predicting , forecasting, and nowcasting is the distance of the speculated future from the present moment occupied by

SECTION 60

#1732765935256

7130-411: The concept of the arrow of time . Historically, the second law was an empirical finding that was accepted as an axiom of thermodynamic theory . Statistical mechanics provides a microscopic explanation of the law in terms of probability distributions of the states of large assemblies of atoms or molecules . The second law has been expressed in many ways. Its first formulation, which preceded

7245-637: The cooler reservoir to the hotter one, which violates the Clausius statement. This is a consequence of the first law of thermodynamics , as for the total system's energy to remain the same; Input + Output = 0 ⟹ ( Q + Q c ) − Q η = 0 {\textstyle {\text{Input}}+{\text{Output}}=0\implies (Q+Q_{c})-{\frac {Q}{\eta }}=0} , so therefore Q c = Q ( 1 η − 1 ) {\textstyle Q_{c}=Q\left({\frac {1}{\eta }}-1\right)} , where (1)

7360-426: The criterion of falsifiability or supplemented it with other criteria, such as verifiability (e.g., verificationism ) or coherence (e.g., confirmation holism ). The scientific method involves experimentation to test the ability of some hypothesis to adequately answer the question under investigation. In contrast, unfettered observation is not as likely to raise unexplained issues or open questions in science, as would

7475-441: The data to be tested are already known, the test is invalid. The above procedure is actually dependent on the number of the participants (units or sample size ) that are included in the study. For instance, to avoid having the sample size be too small to reject a null hypothesis, it is recommended that one specify a sufficient sample size from the beginning. It is advisable to define a small, medium and large effect size for each of

7590-432: The desired intuitive response.) The scenario will typically be designed to target a particular philosophical notion, such as morality, or the nature of the mind or linguistic reference. The response to the imagined scenario is supposed to tell us about the nature of that notion in any scenario, real or imagined. For example, a thought experiment might present a situation in which an agent intentionally kills an innocent for

7705-444: The entropy flux of NBR emission is farther removed from the conduction and convection q / T result, than that for BR emission. This observation is consistent with Max Planck's blackbody radiation energy and entropy formulas and is consistent with the fact that blackbody radiation emission represents the maximum emission of entropy for all materials with the same temperature, as well as the maximum entropy emission for all radiation with

7820-635: The entropy of the system of interest is defined to result from an infinitesimal transfer of heat ( δ Q {\displaystyle \delta Q} ) to the system of interest, divided by the common thermodynamic temperature ( T ) {\displaystyle (T)} of the system of interest and the auxiliary thermodynamic system: Different notations are used for an infinitesimal amount of heat ( δ ) {\displaystyle (\delta )} and infinitesimal change of entropy ( d ) {\displaystyle (\mathrm {d} )} because entropy

7935-411: The entropy spontaneously decreases by means of energy and entropy transfer. When thermodynamic constraints are not present, spontaneously energy or mass, as well as accompanying entropy, may be transferred out of a system in a progress to reach external equilibrium or uniformity in intensive properties of the system with its surroundings. This occurs spontaneously because the energy or mass transferred from

8050-433: The equality The second term represents work of internal variables that can be perturbed by external influences, but the system cannot perform any positive work via internal variables. This statement introduces the impossibility of the reversion of evolution of the thermodynamic system in time and can be considered as a formulation of the second principle of thermodynamics – the formulation, which is, of course, equivalent to

8165-414: The existence of a relation may be assumed. Otherwise, any observed effect may be due to pure chance. In statistical hypothesis testing, two hypotheses are compared. These are called the null hypothesis and the alternative hypothesis . The null hypothesis is the hypothesis that states that there is no relation between the phenomena whose relation is under investigation, or at least not of the form given by

8280-400: The fact) thought experiments – the term prefactual was coined by Lawrence J. Sanna in 1998 – speculate on possible future outcomes, given the present, and ask "What will be the outcome if event E occurs?". Counterfactual (contrary to established fact) thought experiments – the term counterfactual was coined by Nelson Goodman in 1947, extending Roderick Chisholm 's (1946) notion of

8395-433: The factory from the local electric grid. In addition, humans may directly play, in whole or in part, the role that the robotic machinery plays in manufacturing. In this case, instructions may be involved, but intelligence is either directly responsible, or indirectly responsible, for the direction or application of work in such a way as to counteract the tendency towards disorder and uniformity. There are also situations where

8510-404: The flow of heat in steam engines (1824). The centerpiece of that analysis, now known as a Carnot engine , is an ideal heat engine fictively operated in the limiting mode of extreme slowness known as quasi-static, so that the heat and work transfers are between subsystems that are always in their own internal states of thermodynamic equilibrium . It represents the theoretical maximum efficiency of

8625-438: The former and denies the latter. The second law may be formulated by the observation that the entropy of isolated systems left to spontaneous evolution cannot decrease, as they always tend toward a state of thermodynamic equilibrium where the entropy is highest at the given internal energy. An increase in the combined entropy of system and surroundings accounts for the irreversibility of natural processes, often referred to in

8740-417: The formulation of a crucial experiment to test the hypothesis. A thought experiment might also be used to test the hypothesis. In framing a hypothesis, the investigator must not currently know the outcome of a test or that it remains reasonably under continuing investigation. Only in such cases does the experiment, test or study potentially increase the probability of showing the truth of a hypothesis. If

8855-451: The formulation of the principle in terms of entropy. The zeroth law of thermodynamics in its usual short statement allows recognition that two bodies in a relation of thermal equilibrium have the same temperature, especially that a test body has the same temperature as a reference thermometric body. For a body in thermal equilibrium with another, there are indefinitely many empirical temperature scales, in general respectively depending on

8970-410: The four combinations of either entropy (S) up or down, and uniformity (Y) – between system and its environment – up or down. This 'special' category of processes, category IV, is characterized by movement in the direction of low disorder and low uniformity, counteracting the second law tendency towards uniformity and disorder. The second law can be conceptually stated as follows: Matter and energy have

9085-422: The future to the present to reveal the mechanism through which that particular specified future could be attained from the present. Backcasting is not concerned with predicting the future: The major distinguishing characteristic of backcasting analyses is the concern, not with likely energy futures, but with how desirable futures can be attained. It is thus explicitly normative , involving 'working backward' from

9200-460: The historical development of Judeo-Christian morality, with the intent of questioning its legitimacy. An early written thought experiment was Plato 's allegory of the cave . Another historic thought experiment was Avicenna 's " Floating Man " thought experiment in the 11th century. He asked his readers to imagine themselves suspended in the air isolated from all sensations in order to demonstrate human self-awareness and self-consciousness , and

9315-644: The history of modern science. This is widely thought to have been a straightforward physical demonstration, involving climbing up the Leaning Tower of Pisa and dropping two heavy weights off it, whereas in fact, it was a logical demonstration, using the thought experiment technique. The experiment is described by Galileo in Discorsi e dimostrazioni matematiche (1638) (from Italian : 'Mathematical Discourses and Demonstrations') thus: Salviati . If then we take two bodies whose natural speeds are different, it

9430-470: The hypothesized relation, positive or negative, is fixed in advance). Conventional significance levels for testing hypotheses (acceptable probabilities of wrongly rejecting a true null hypothesis) are .10, .05, and .01. The significance level for deciding whether the null hypothesis is rejected and the alternative hypothesis is accepted must be determined in advance, before the observations are collected or inspected. If these criteria are determined later, when

9545-406: The instructions, as well as the source of work may be internal or external to the system, and they may or may not cross the system boundary. To illustrate, the instructions may be pre-coded and the electrical work may be stored in an energy storage system on-site. Alternatively, the control of the machinery may be by remote operation over a communications network, while the electric work is supplied to

9660-536: The integrand (đQ/T) of the Clausius expression applies to heat conduction and convection, and the case of ideal infinitesimal blackbody radiation (BR) transfer, but does not apply to most radiative transfer scenarios and in some cases has no physical meaning whatsoever. Consequently, the Clausius inequality was re-stated so that it is applicable to cycles with processes involving any form of heat transfer. The entropy transfer with radiative fluxes ( δ S NetRad \delta S_{\text{NetRad}} )

9775-431: The intended interpretation usually guides the construction of the theoretician". It is, however, "possible and indeed desirable, for the purposes of logical clarification, to separate the two steps conceptually". When a possible correlation or similar relation between phenomena is investigated, such as whether a proposed remedy is effective in treating a disease, the hypothesis that a relation exists cannot be examined

9890-402: The internal energy of a closed system that was initially in its own internal thermodynamic equilibrium. In 1926, Max Planck wrote an important paper on the basics of thermodynamics. He indicated the principle This formulation does not mention heat and does not mention temperature, nor even entropy, and does not necessarily implicitly rely on those concepts, but it implies the content of

10005-460: The mathematics), thereby starting quantum theory. A non-equilibrium statistical mechanics approach has also been used to obtain the same result as Planck, indicating it has wider significance and represents a non-equilibrium entropy. A plot of K v versus frequency (v) for various values of temperature ( T) gives a family of blackbody radiation energy spectra, and likewise for the entropy spectra. For non-blackbody radiation (NBR) emission fluxes,

10120-425: The network but link certain points of the latter with specific places in the plane of observation. By virtue of those interpretative connections, the network can function as a scientific theory." Hypotheses with concepts anchored in the plane of observation are ready to be tested. In "actual scientific practice the process of framing a theoretical structure and of interpreting it are not always sharply separated, since

10235-463: The original idea of combining bodies of different weights. Thought experiments have been used in philosophy (especially ethics), physics , and other fields (such as cognitive psychology , history, political science , economics, social psychology , law, organizational studies , marketing, and epidemiology ). In law, the synonym "hypothetical" is frequently used for such experiments. Regardless of their intended goal, all thought experiments display

10350-440: The outcome of an experiment in a laboratory setting or the observation of a phenomenon in nature . The prediction may also invoke statistics and only talk about probabilities. Karl Popper , following others, has argued that a hypothesis must be falsifiable , and that one cannot regard a proposition or theory as scientific if it does not admit the possibility of being shown to be false. Other philosophers of science have rejected

10465-496: The proper definition of entropy and was based on caloric theory , is Carnot's theorem , formulated by the French scientist Sadi Carnot , who in 1824 showed that the efficiency of conversion of heat to work in a heat engine has an upper limit. The first rigorous definition of the second law based on the concept of entropy came from German scientist Rudolf Clausius in the 1850s and included his statement that heat can never pass from

10580-418: The properties of a particular reference thermometric body. The second law allows a distinguished temperature scale, which defines an absolute, thermodynamic temperature , independent of the properties of any particular reference thermometric body. The second law of thermodynamics may be expressed in many specific ways, the most prominent classical statements being the statement by Rudolf Clausius (1854),

10695-534: The relevant question is not whether or not the man understands Chinese, but more broadly, whether a functionalist theory of mind is correct. It is generally hoped that there is universal agreement about the intuitions that a thought experiment elicits. (Hence, in assessing their own thought experiments, philosophers may appeal to "what we should say," or some such locution.) A successful thought experiment will be one in which intuitions about it are widely shared. But often, philosophers differ in their intuitions about

10810-401: The requirement of conservation of energy as expressed in the first law of thermodynamics and provides necessary criteria for spontaneous processes . For example, the first law allows the process of a cup falling off a table and breaking on the floor, as well as allowing the reverse process of the cup fragments coming back together and 'jumping' back onto the table, while the second law allows

10925-410: The researcher already knows the outcome, it counts as a "consequence" — and the researcher should have already considered this while formulating the hypothesis. If one cannot assess the predictions by observation or by experience , the hypothesis needs to be tested by others providing observations. For example, a new technology or theory might make the necessary experiments feasible. A trial solution to

11040-412: The results from their subsequent, real, physical experiment differed from those of their prior, imaginary experiment. The English term thought experiment was coined as a calque of Gedankenexperiment , and it first appeared in the 1897 English translation of one of Mach's papers. Prior to its emergence, the activity of posing hypothetical questions that employed subjunctive reasoning had existed for

11155-477: The same energy radiance. Second law analysis is valuable in scientific and engineering analysis in that it provides a number of benefits over energy analysis alone, including the basis for determining energy quality (exergy content ), understanding fundamental physical phenomena, and improving performance evaluation and optimization. As a result, a conceptual statement of the principle is very useful in engineering analysis. Thermodynamic systems can be categorized by

11270-406: The same way one might examine a proposed new law of nature. In such an investigation, if the tested remedy shows no effect in a few cases, these do not necessarily falsify the hypothesis. Instead, statistical tests are used to determine how likely it is that the overall effect would be observed if the hypothesized relation does not exist. If that likelihood is sufficiently small (e.g., less than 1%),

11385-416: The scenario. Other philosophical uses of imagined scenarios arguably are thought experiments also. In one use of scenarios, philosophers might imagine persons in a particular situation (maybe ourselves), and ask what they would do. For example, in the veil of ignorance , John Rawls asks us to imagine a group of persons in a situation where they know nothing about themselves, and are charged with devising

11500-404: The second law. A closely related statement is that "Frictional pressure never does positive work." Planck wrote: "The production of heat by friction is irreversible." Not mentioning entropy, this principle of Planck is stated in physical terms. It is very closely related to the Kelvin statement given just above. It is relevant that for a system at constant volume and mole numbers , the entropy

11615-399: The sign convention of heat is used in which heat entering into (leaving from) an engine is positive (negative) and (2) Q η {\displaystyle {\frac {Q}{\eta }}} is obtained by the definition of efficiency of the engine when the engine operation is not reversed. Thus a violation of the Kelvin statement implies a violation of the Clausius statement, i.e.

11730-404: The spectral entropy radiance L v is found by substituting K v spectral energy radiance data into the L v expression (noting that emitted and reflected entropy fluxes are, in general, not independent). For the emission of NBR, including graybody radiation (GR), the resultant emitted entropy flux, or radiance L , has a higher ratio of entropy-to-energy ( L/K ), than that of BR. That is,

11845-467: The statement by Lord Kelvin (1851), and the statement in axiomatic thermodynamics by Constantin Carathéodory (1909). These statements cast the law in general physical terms citing the impossibility of certain processes. The Clausius and the Kelvin statements have been shown to be equivalent. The historical origin of the second law of thermodynamics was in Sadi Carnot 's theoretical analysis of

11960-596: The subsystems, and then some operation makes the walls more permeable, then the system spontaneously evolves to reach a final new internal thermodynamic equilibrium , and its total entropy, S {\displaystyle S} , increases. In a reversible or quasi-static , idealized process of transfer of energy as heat to a closed thermodynamic system of interest, (which allows the entry or exit of energy – but not transfer of matter), from an auxiliary thermodynamic system, an infinitesimal increment ( d S {\displaystyle \mathrm {d} S} ) in

12075-455: The system may become more ordered or complex, by the combination of two things, a work or exergy source and some form of instruction or intelligence. Where 'exergy' is the thermal, mechanical, electric or chemical work potential of an energy source or flow, and 'instruction or intelligence', although subjective, is in the context of the set of category IV processes. Consider a category IV example of robotic manufacturing and assembly of vehicles in

12190-427: The system moves further away from uniformity with its warm surroundings or environment (category IV). The main point, take-away, is that refrigeration not only requires a source of work, it requires designed equipment, as well as pre-coded or direct operational intelligence or instructions to achieve the desired refrigeration effect. Before the establishment of the second law, many people who were interested in inventing

12305-504: The system to its surroundings results in a higher entropy in the surroundings, that is, it results in higher overall entropy of the system plus its surroundings. Note that this transfer of entropy requires dis-equilibrium in properties, such as a temperature difference. One example of this is the cooling crystallization of water that can occur when the system's surroundings are below freezing temperatures. Unconstrained heat transfer can spontaneously occur, leading to water molecules freezing into

12420-443: The system will move with a speed less than eight; but the two stones when tied together make a stone larger than that which before moved with a speed of eight. Hence the heavier body moves with less speed than the lighter; an effect which is contrary to your supposition. Thus you see how, from your assumption that the heavier body moves more rapidly than the lighter one, I infer that the heavier body moves more slowly. The common goal of

12535-411: The system, because a chemical reaction may be in progress, or because heat transfer actually occurs only irreversibly, driven by a finite difference between the system temperature ( T ) and the temperature of the surroundings ( T surr ). The equality still applies for pure heat flow (only heat flow, no change in chemical composition and mass), which is the basis of the accurate determination of

12650-417: The system, which is evident from ordinary experience of refrigeration , for example. In a refrigerator, heat is transferred from cold to hot, but only when forced by an external agent, the refrigeration system. Lord Kelvin expressed the second law in several wordings. Suppose there is an engine violating the Kelvin statement: i.e., one that drains heat and converts it completely into work (the drained heat

12765-404: The tendency to reach a state of uniformity or internal and external equilibrium, a state of maximum disorder (entropy). Real non-equilibrium processes always produce entropy, causing increased disorder in the universe, while idealized reversible processes produce no entropy and no process is known to exist that destroys entropy. The tendency of a system to approach uniformity may be counteracted, and

12880-517: The term semifactual was coined by Nelson Goodman in 1947 – speculate on the extent to which things might have remained the same, despite there being a different past; and asks the question Even though X happened instead of E, would Y have still occurred? (e.g., Even if the goalie had moved left, rather than right, could he have intercepted a ball that was traveling at such a speed?). Semifactual speculations are an important part of clinical medicine. The activity of prediction attempts to project

12995-428: The term "hypothesis". In its ancient usage, hypothesis referred to a summary of the plot of a classical drama . The English word hypothesis comes from the ancient Greek word ὑπόθεσις hypothesis whose literal or etymological sense is "putting or placing under" and hence in extended use has many other meanings including "supposition". In Plato 's Meno (86e–87b), Socrates dissects virtue with

13110-417: The user. Whilst the activity of nowcasting, defined as "a detailed description of the current weather along with forecasts obtained by extrapolation up to 2 hours ahead", is essentially concerned with describing the current state of affairs, it is common practice to extend the term "to cover very-short-range forecasting up to 12 hours ahead" (Browning, 1982, p.ix). The activity of hindcasting involves running

13225-539: Was the first to use the equivalent German term Gedankenexperiment c.  1812 . Ørsted was also the first to use the equivalent term Gedankenversuch in 1820. By 1883, Ernst Mach used Gedankenexperiment in a different sense, to denote exclusively the imaginary conduct of a real experiment that would be subsequently performed as a real physical experiment by his students. Physical and mental experimentation could then be contrasted: Mach asked his students to provide him with explanations whenever

#255744