HEMPEL'S COVERING LAW THEORY AND THERMODYNAMICS

BY

DR. EGBAI, U. OJAHDEPARTMENT OF PHILOSOPHY

UNIVERSITY OF CALABARCALABAR

ABSTRACTThis paper attempts to apply the covering law model of explanation championed by the German-born American philosopher Carl GustarHempel to the laws of thermodynamics, a science that describes much of time-asymmetric behavior found in the world. Hempel's popular covering law model of explanation suggests that a particular event is explained if its occurrence can be deduced from the occurrence of other particular events, with the help of one or more laws. He radically assigned the same logical structure to explanation and prediction. The juxtaposition of symmetrical Hempel's covering law model of explanation with the laws of thermodynamics (especially the second law which deals with time-asymmetry), is intended to examined the popularity of this deductive nomological (covering law) model of explanation and to suggest a way forward should the one in consideration fail to represent what scientific explanation ought to be. If all scientific endeavours involve some forms of thermodynamics processes, and the second law of thermodynamics says there cannot be 100% efficiency in any thermodynamic process, to what extent can we trust explanations and predictions in science? The focus of this paper is therefore to attempt a response to this critical question, which will deepen our epistemic appreciation of science.

INTRODUCTIONPhilosophers have written much about the structure and function of scientific

explanation. One of the most important aim of science is to try and explain what happens in the world around us. Sometimes we seek explanations for practical ends. For example we might want to know why the Ozone layer is being depleted so quickly, in order to try and do something about it. In other cases, we seek scientific explanations simply to satisfy our intellectual curiosity- we want to understand more about how the world works. Historically, the pursuit of scientific explanation has been motivated by both goals. Quite often, modern science is successful in its aim of supplying explanation. For example, chemists can explain why sodium turns yellow when it burns, Astronomers can explain why solar eclipses occur when they do. Economist can explain why the Naira decline in value in recent times,etc (Okasah, 40).

With the decline of logical positivism and, empiricism the theory of explanation, like most other pars of philosophy of science, has began to break out of its former narrowness so as to grapple with the wealth of evidence provided by the actual modes of scientific explanation. In such periods of change of emphasis, however, there is always the risk of over-reaction; one may loose nearly as much as one gets. The fact that the universe is expanding is a scientific fact of our time and should not just be taken for granted. A good theory about the expanding universe could solve contemporary problems. It is hoped that this paper will open up avenues for more

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studies in the laws of thermodynamics (especially as it relates to the science of cosmology among others). A suitable explanation of the laws of thermodynamics will help to demystify some unseal occurrences in the universe and make clearer the understanding of what the expansion of the universe is all about, the depletion of the Ozone layer and its implications on global warming. The paper will also attempt to discover if there could be reliable and realistic unusual occurrences that could effectively be explained. It will also provide epistemic direction towards tackling these unusual changes.

SCIENTIFIC EXPLANATIONHempel and Oppenheim's essay “Studies in the Logic of Explanation”, published in Vol. 15

of the Journal: Philosophy of Science, gave account of the deductive-nomological explanation. A scientific explanation of a fact is a deduction of statement (called the explanadum) that describes the fact that we want to explain, the premises (called the explanans) are scientific laws and suitable initial conditions. For an explanation to be acceptable, the explanand must be true.

According to the deductive-nomological model of explanation, a fact is thus reduced to a logical relationship between statements: the explanandum is a consequence of the explanans. As it is typical of the philosophy of logical positivism, pragmatic aspects of explanation are not in any way taken into consideration. Another feature is that an explanation requires scientific laws; facts are explained when they are subsumed under laws. Every generalized statement which is a logical consequence of a fundamental theory is a derived theory. This is poised so as to give the nature of scientific laws. The underlying idea for this definition is that a scientific theory deals with general properties expressed by universal statements. References to specific space-time regions or to individual things are not allowed. Thus, there is a distinction between a fundamental theory, which is universal without restrictions and a derived theory that can contain a reference to individual objects. From a realistic point of view, these scientific laws are not tools to make predictions, but they are genuine statements that describe the world.

Another characteristic of the Hempel-Oppeheim model is that explanation and prediction have exactly the same logical structure. An explanation can be used to forecast and a forecast is a valid explanation (Feyman, 48). The deductive nomological model also accounts for the explanation of laws. In that case, the explanandum is a scientific law and can be proved with the help of other scientific laws. Hempel's “Aspects of Scientific Explanation”, faces the problem of inductive explanation, in which the explanans include statistical laws. According to Hempel, in such explanation the explanans give only a high degree of probability to the explanadum, which is not a logical consequence of the premises. Take for instance:

The relative frequency of P with respect to Q is rThe object A belong to PThus, A belong to Q

The conclusion “A belongs to Q” is not certain, for it is not a logical consequence of the two premises. According to Hempel, this explanation gives a degree of probability r to the conclusion. Note that the inductive explanation requires a covering law: the fact is explained by means of scientific laws. But now the laws are not deterministic, statistical laws are admissible. However, in many respects, the inductive explanation is similar to the deductive explanation.

Both deductive and inductive explanations are nomological ones (that is, they require universal laws). The relevant fact is the logical relation between the explanans and the explanandum, in deductive explanation, the latter is a logical consequence of the former,

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whereas in inductive explanation, the relationship is different. But in either model, only logical aspects are relevant, pragmatic features are not taken into account. The symmetry between explanation and prediction is preserved. The explanans must be true.

THE LAWS OF THERMODYNAMICSThe word thermodynamics was coined by James Joule from two Greek words therme

meaning “heat” and dynamis meaning “power” (Tolman 6). Thermodynamics is the study of energy conversion between heat and mechanical work, and subsequently the microscopic variables such as temperature, volume and pressure (Sklar, 18).

The starting point of most thermodynamic considerations are the laws of thermodynamics, which postulates that energy can be exchanged between physical systems as heat or work. The entropy, which can be defined for any isolated system that is in thermodynamic equilibrium. These laws, have become some of the most important in all of physics and other associated sciences. The four widely accepted principles of thermodynamics include:a. The Zeroth Law of Thermodynamic, which underlies the definition of temperature,

states that:if object A is in thermal equilibrium with object B, and object B is in thermal equilibrium with object C, then object C is also in thermal equilibrium with object A.

This law allows for the building of thermometer. When two systems are each in thermal equilibrium with a third system, the first two systems are in thermal equilibrium with each other. This property makes it meaningful to use thermometers as the “third system” and to define temperature scale.

b. The First Law of Thermodynamics (The Law of Conservation of Energy)This law states that,The change in a system's internal energy is equal to the difference between heat added to

the system from its surroundings and work done by the system on its surroundings. This law mandates conservation of energy and that the flow of heat is a form of energy transfer. It can simply be stated this way:

Energy can neither be created nor destroyed but may be converted from one form to another

The internal energy, U of a system, which is the sum of all the energies of the system, changes when heat is evolved or absorbed, and/or work is done on, or by the system

c. The Second Law of ThermodynamicsEntropy, means a measure of the degree of disorder or randomness of a substance, is

presumed to be variable that increases but never decreases in all of the ordinary physical processes that never occur in reverse. This assumption leads to the statement of the second law:

The total entropy of an isolated system (the thermal energy per unit temperature that is unavailable for doing useful work) can never decrease.

Heat does not follow spontaneously from a colder region to a hotter region, or, equivalently, heat at a given temperature cannot be converted entirely into work. Consequently, the entropy of a closed system, or heat energy per unit temperature, increases

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over time toward some maximum value. Thus, all closed systems tend toward an equilibrium state in which entropy is at a maximum and no energy is available to do useful work. This asymmetry between forward and backward processes gives rise to what is known as the “arrow of time”. It states that a spontaneous process occurs only if there is an increase in the entropy of a system and its surrounding.

d. The Third Law of ThermodynamicsAs a system asymptotically approaches absolute zero of temperature all processes

virtually cease and the entropy of the system asymptotically approach a minimum value; also stated as follows:

The entropy of all systems and of all states of a system is zero at absolute zero.Or,It is impossible to reach the absolute zero of temperature by any finite number of processes.Or,The entropy of a perfect crystal of an element in its most stable form tends to zero as the temperature approached absolute zero.

oAbsolute zero, at which all activity would stop if it were possible to happen, is -273.15 C o(degree Celsius), or -459.67 F (degrees Fahrenheit), or 0K (kelvins, formerly sometimes degrees

absolute). (Pippard 64)This allows an absolute scale for entropy to be established that, from a statistical point of

view, determines the degree of randomness or disorder in a system.

COVERING LAW AND THERMODYNAMICSHempel's popular covering law model of explanation suggest that a particular event is

explained if its occurrences can be deduced from the occurrence of other particular events, with the help of one or more laws. Hempel holds that the structure of a scientific explanation is essentially the same whether the explanandum is particular or general,. He allows a scientific explanation could appeal to particular facts as well as general laws, but holds that at least one general law is always essential. Hempelasserts that every scientific explanation is potentially a prediction. For him, explanation and prediction are structurally symmetric. The covering law model implies that explanation should be symmetrical in relation.He seems not to agree that connections between causes and effects may be merely probabilistic. The question is whether the covering law model fully captures what a scientific explanation is in totality?

His account of scientific explanation appears to be limited when applied to thermodynamic processes in science. The science of thermodynamics seems to give a concise, powerful and general account of the time asymmetry of ordinary physical processes found in the world. In a world possibly governed by time-symmetric laws, how should we understand time-asymmetric laws of thermodynamic? Thermodynamic asymmetry in time affirms that microscopic processes appear to be temporarily “directed” in some sense.Systems spontaneously evolve to future equilibrium states, but they do not spontaneously evolve away from equilibrium states. The nature of this directedness raises many questions at the foundations of philosophy of science.

Since the covering law model of explanation purports a symmetrical relation it may fall short of what scientific explanation holds for thermodynamics, there are asymmetries in life;

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casual asymmetries, time asymmetries and the rest. There must be another way of designating what scientists call explanation, which is more encompassing than the covering law model of explanation. A recourse to causal explanation may involve less risk and achieve more success.

CONCLUSIONThe problem of scientific explanation goes beyond the epistemological considerations

but reaches far into the metaphysical issues in philosophy of science. Most recent discussions on scientific explanation are laden with the presupposition that science sometimes provides explanation rather than something that falls short of explanation, say for instance, mere description. The history of science is replete with scientific theories which have turned out to be false. This seems to provide some grounds for one to argue then that the realist view of an independent reality might be incorrect. It is plausible then for someone like David Papineau to infer that by what he called a “pessimistic meta-induction” that since past scientific theories have normally turn out to be false, present and future scientific theories are likely to be false too (science, problems of the society, 809), will it then be out of place to respond to this problem by asserting that successful theories are merely approximations to truth and not absolute truths. It is on the basis of this that scientific laws and theories can be said to be probabilistic as this put science in the anchor of verisimilitude.

WORKS CITEDHempel, C. G.,Aspects of Scientific Explanation and other Essays in the Philosophy of Science. New

York: Free Press, 1965.

Papineau David, Problems of Philosophy of Science. Ted Honderish (ed.) The Oxford Companion to Philosophy. Oxford: Oxford University Press, 1995.

Pippard, A.,The Elements of Classical Thermodynamics. Cambridge: Cambridge, University Press, 1964.

Samir, Okasha,Philosophy of Science: A very short introduction. New York: Oxford University Press, 2002.

Sklar, L., Philosophy and Space-time physics. Los Angeles: UCLA Press, 1985.

Tolman, R.,Relativity, Thermodynamics and Cosmology.Oxford: Oxford University Press, 1934.

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