The Second Law of Thermodynamics
in the Context of the Christian Faith

Allan H. Harvey


This essay was written in response to questions that came up on the Science and Christianity mailing list touching on issues of entropy and/or the second law of thermodynamics. I found myself writing the same things repeatedly to straighten out various misconceptions. So, I have written something between a personal essay and a FAQ on the topic. Since this is written from my personal viewpoint, I will start by stating my background and personal convictions which cannot help but influence what I write.

I have a Ph.D. in Chemical Engineering (UC-Berkeley, 1988), specializing in "Molecular Thermodynamics" and the thermophysical properties of fluids. I then did two years of postdoctoral work, more or less in Chemical Physics, followed by four years in private industry. I now work at a U.S. Government (civilian) acience lab. [Nothing I say here should be construed as representing my employer or the US Government.] I do not consider myself a specialist specifically in the second law, but my overall expertise in thermodynamics is sufficient to shed light on the relevant issues.

I am an evangelical Christian. I believe the Bible to be trustworthy in conveying God's messages. Where people get into trouble is when, for example, they take the message of Genesis 1 (that God created everything, including us) and try to read it as something it is not (i.e., a science text). I get annoyed at the silly arguments of "creation science," but what is more annoying is when non-Christians see those arguments and get the false impression that such issues (rather than Christ) are what Christianity is all about. I do believe that God created everything, but how and when and to what extent that involved his sovereignty over "natural" processes are secondary questions that should not divide the church.

Finally, I should add that God has given me a passion for truth. Truth in all things, since all truth is God's truth. I therefore welcome correction or constructive criticism on this document.

What are the Laws of Thermodynamics?

First, we need a few definitions. In thermodynamics, we must refer to a clearly defined system. Textbooks commonly consider the system to be the contents of a box-like container. But we could also define it to be a specific cubic meter of the atmosphere above Phoenix, or the Earth (provided we define the boundary precisely), or my left kidney. Everything in the universe that is not a part of the system is the surroundings. Systems are divided into three categories: an isolated system can exchange neither matter nor energy with its surroundings, a closed system can exchange energy but not matter, and an open system can exchange both energy and matter. The Earth, for example, is an open system, but might be considered closed if one neglected meteors, space probes, etc. It is not an isolated system because, among other things, it receives radiant energy from the Sun. [NOTE: this categorization is not universally used; in particular it is not uncommon to hear an isolated system as defined above described as "closed."]

The first law of thermodynamics, also known as the law of conservation of energy, states that the total energy of any system remains the same, except to the extent it exchanges energy with its surroundings. This exchange can be in the form of heat transfer (perhaps by placing a hot body in thermal contact with the system) or work (perhaps by compressing the system via a piston). This gets modified a little for matter/energy conversion (important if the system is the Sun), but it is basically the simple idea that energy is never created or destroyed.

The second law is trickier. There are many statements of it; perhaps the simplest is that it is impossible for there to exist any process whose only effect is to transfer energy from a system at a low temperature to one at a higher temperature. In other words, heat flows downhill. The 2nd law is also formulated in terms of entropy, a well-defined quantity in terms of heat flows and temperature. Another statement of the 2nd law is that, for any isolated system, the entropy remains the same during any reversible process and increases during any irreversible process. The 2nd law also places bounds on the entropy change in a non-isolated system in relation to the temperatures of the system and the surroundings and the amount of energy leaving or entering it, but it is important to note that a system can experience a decrease in entropy if it is exchanging energy with its surroundings. The 2nd law is ultimately a statement about heat flows, work, and temperature, and also about the direction of time. It states that, as time goes forward, the overall effect is for energy to dissipate from hot things to cold things.

The third law concerns changes in entropy as the temperature approaches absolute zero, and indirectly can be used to show the impossibility of attaining absolute zero. It does not come up in the contexts of concern in this essay.

For those who want to learn more, I recommend The Second Law, by P.W. Atkins, Scientific American Books, New York, 1994. This is a well-written popular introduction to the subject. The reader is cautioned, however, that Atkins has a bias toward metaphysical naturalism which sometimes leads him to extrapolate from the science to unfounded metaphysical conclusions. If you can ignore the philosophy and stick to the science, you will learn a lot from his book. A good exposition at a higher technical level is given in the introductory chapters of Entropy, by J.D. Fast, McGraw Hill, 1962. [NOTE: Fast's classic work should not be confused with a book of the same title written around 1980 by the gadfly Jeremy Rifkin.] Of course any college textbook on thermodynamics will cover these topics.

A Brief History of the Second Law

Some of the following information is adapted from Ira N. Levine, Physical Chemistry, McGraw-Hill, 1978.

Something that was roughly the 2nd law was stated by French engineer Sadi Carnot in 1824 with regard to the efficiency of steam engines. [Carnot may also have been the first to postulate the 1st law, but he never published that and got no credit until long after his death.] Carnot's work was almost universally ignored, but was rediscovered (and stripped of its tie to the pre-1st-law "caloric" theory of heat) in the 1840's. Around 1850 came the first rigorous statements of the 2nd law by William Thomson (Lord Kelvin) and Rudolph Clausius. It was Clausius who first defined the quantity entropy and coined the word (from a Greek word meaning "transformation"). He made the often-quoted brief statement of the first and second laws: "Die Energie der Welt ist Konstant. Die Entropie der Welt strebt einem Maximum zu." [rough translation: The energy of the world (more properly, an isolated system) is constant. The entropy of the world strives toward a maximum.] Maxwell made his contributions a little later, followed by Boltzmann. Their main contributions here were in tying things to the concept of molecules (including the science of statistical mechanics, which they basically invented though Gibbs brought it to maturity), which was not a part of the thinking of people like Kelvin and Clausius.

The Second Law and Creation

Now we address the context in which the 2nd law arises in creation arguments. The usual argument goes something like this: "The 2nd law says everything tends toward increasing entropy (randomness and disorder). But the evolution of life involves the development of great complexity and order. Therefore, evolution is impossible by the 2nd law of thermodynamics." While it sounds simple, there are major flaws in this argument that render it worthless.

The Earth is Not an Isolated System

It is only in isolated systems that entropy must increase. Systems that can exchange energy with their surroundings have no such restriction. For example, water can freeze into ice (becoming more ordered and decreasing its entropy) by giving up heat to its surroundings (this increases the entropy of the surroundings, of course). In the case of the Earth, the Sun is a major source of energy, and the Earth also radiates energy into space. One consequence of thermodynamics is that, when energy comes from a "hot" source (like the Sun) and is output to a "cold" reservoir (like space), it can be used to do work, which means that "complexity" or "order" can be produced. The main point is that, for a non-isolated system, an increase in "complexity" (to the extent one can connect that concept with the thermodynamic entropy, which is far from straightforward for living creatures) does not necessarily indicate a violation of the 2nd law. A good example is the development of a human fetus into an adult; this is the production of a more thermodynamically complex system but involves no violation of the laws of thermodynamics.

It is worth mentioning here that the usual reply to creationists that "the second law doesn't apply to non-isolated systems" is not quite correct. The second law always applies; in fact, it was originally developed for non-isolated systems (the working fluid of a heat engine). The key point is that it is only in isolated systems that the second law takes the simplified "entropy must increase" form. For non-isolated systems, the second law still applies as a statement about heat flows and temperatures, just not in the form used in creationist arguments.

An Internal Inconsistency

Some creationists assert that advanced (especially human) life represents a decrease in entropy which violates the 2nd law, and they therefore invoke intervention by God, who is outside the laws of thermodynamics. They also, however, generally assert that this particular "intervention" stopped with the creation of man, and that (with the exception of the occasional miracle) God has allowed things to develop in accordance with the laws of thermodynamics and other physical laws since then.

These two assertions are, however, mutually inconsistent. The reason is that the thermodynamic entropy is strictly an additive quantity. If the 2nd law has not been violated as the number of humans grew from two to 6 billion, it is ridiculous to assert that it was violated in the comparatively minuscule change from zero to two. If we say that the first two humans represented a violation of the 2nd law, the logical conclusion would be that God must be continually intervening in violation of the 2nd law in order to increase the number of humans on Earth. While God is certainly capable of this, there is no evidence to suggest that such violations are happening as complex life forms like humans reproduce and increase in number. [NOTE: All this is not to say that God's creation of human life was not miraculous. My only point is that the specific assertion that the existence of human life in and of itself violates the 2nd law is unfounded.]

What About the Universe?

An occasional creationist response to the first flaw mentioned above is to say that, while the Earth is not an isolated system, the universe as a whole is. However, this does not help the argument they are trying to make. Astrophysicists, using data such as the cosmic background radiation, have verified that the universe has obeyed the second law of thermodynamics very well since the time of the big bang. The 2nd law predicts that something small and hot should become larger and colder, and that is just what has happened. The existence of some ordered life in a little corner of the universe like ours is a drop in the bucket - when the whole system is considered (which one must always do in thermodynamics), there is no violation of the second law in the development of the universe.

So what about "before" the inception of the universe? Can it be said that bringing into existence the hot, pointlike early universe from nothing was a violation of the 2nd law? While that argument has a certain appeal, and I believe the creation of the universe to have been miraculous, I think a 2nd-law argument is inappropriate here as well. The 2nd law is an attribute of the physical universe, describing how systems go with time. Modern physics tells us that the physical universe is not just space but also contains time as a fundamental dimension. The process by which all that came to be is not something that can be addressed by the laws (including the laws of thermodynamics) characterizing the resulting universe.

What About Information Theory?

Since their arguments do not work in terms of thermodynamics, some anti-evolutionists turn to information theory, which contains a quantity called "entropy." While I am no expert in information theory, I can offer some relevant comments.

As a preliminary, we must talk about the definition of entropy from statistical physics. This definition is mostly due to Boltzmann, and is even engraved on his tombstone. He defined the entropy of a system in terms of the number of different states available to it. So, for example, the expansion of a gas into double its original volume at constant temperature would represent an increase in entropy, because each molecule would have twice as much volume (and therefore twice as many "states") accessible to it. It is this definition that causes entropy to be thought of in terms of "disorder," because a highly ordered system like a crystal has fewer available states. Boltzmann's identification of this quantity with the thermodynamic entropy is now universally accepted.

More recently, a field has arisen called information theory. This deals with, among other things, quantifying the "information content" of various systems. Some of the results of information theory resemble the results of statistical physics, so much so that in certain well-defined conditions a quantity can be defined that is labeled "entropy" and that obeys something analogous to the 2nd law. While the identification of the information entropy with its thermodynamic counterpart is controversial, it is plausible enough to be taken seriously.

So some creationists, recognizing that their argument fails for the thermodynamic entropy, assert it in terms of the information entropy, which talks about things related to "complexity" and "disorder." It still doesn't work. First, there are real problems, without satisfactory solutions thus far, in quantifying the information entropy of living things. Someday this may be do-able, but right now science is not sufficiently well-developed to make definitive statements with regard to information entropy and life. Second, the first flaw mentioned above still applies in that the systems under consideration are not isolated. This means that, even if one can apply a "second law" to them, it will not be in the simple "entropy must increase" form valid for isolated systems. Finally, I can mention that, contrary to statements one finds in the creationist literature, genetic "information" (by reasonable definitions of the term) in living creatures can increase via natural processes.

What about "Energy Conversion Mechanisms"?

A few of those invoking the 2nd law to oppose evolution have recognized the isolated system problem, and responded by saying that for work and structure to be produced in a system, it is not enough to have energy flow, one must also have an "energy conversion mechanism." This statement is actually correct, but it does not help the anti-evolution cause. The biochemistry of life is full of such mechanisms (a more standard name is "dissipative structures"). Photosynthesis is one example, as are other pieces of the biochemistry of the cell. With these structures in place (in other words, once life exists), there is then no obstacle from the standpoint of thermodynamics to the evolution of more and different life.

One might, of course, ask about the origin of these dissipative structures. This is a legitimate question, though not really one of "evolution" (which normally refers to the development of life from other life) but instead one of "abiogenesis." Whether or not the biochemistry of life could arise "naturally" is one where the evidence is not so clear, and legitimate arguments can be made here. However, at this level the arguments are primarily about plausibility of chemical mechanisms rather than thermodynamics (and those who use them should not say their position is based on thermodynamics), so they are outside the scope of this essay.

Other Abuses of the Second Law

A common misuse of the 2nd law occurs in connection with events that are highly improbable. An example is the hypothetical origin of life from normal chemical processes, which has been compared to unlikely occurrences such as the assembly of a 747 by a tornado passing through a junkyard. That may or may not be an appropriate analogy, but it is definitely mistaken to assert that, simply because it is ridiculously unlikely, the scenario would represent a violation of the 2nd law. The important point is that, while violations of the 2nd law are highly improbable (this improbability is the essence of the 2nd law in the statistical-mechanical formulation), not every improbable event is a violation of the 2nd law. For example, if I flipped a coin 1000 times and came up "heads" each time, it would be highly improbable but would not violate any laws of thermodynamics.

Finally, there is the use of "entropy" in situations where thermodynamics is simply not relevant. One hears entropy invoked as an explanation for everything from my messy desk to the decline of society. That is tolerable and perhaps even useful as a metaphor; certainly there is some similarity between the "decay" and "disorder" in these situations and the thermodynamic consequences of the 2nd law. But we must not mistake metaphor for real physical law. To do so can lead to false and even harmful conclusions, such as when "relativity" is invoked to argue against the idea of absolute right and wrong.

The Second Law, Evil, and the Fall

My final topic is the occasional identification of entropy with "evil" or "death," an identification often accompanied by the assertion that the 2nd law is a consequence of the Fall. I believe that this is wrong for several reasons. [NOTE: I am neutral with regard to the literalness of the Biblical account of the Fall. I am open to the idea that it is a figurative account of mankind's collective rejection of God's authority. For simplicity, this section uses terminology that presumes the literal interpretation. But the arguments are not significantly affected if one takes a less literal view.]

First, I believe the identification of the 2nd law with "evil" is a consequence of some of the misconceptions mentioned above. We identify God (and therefore good) with "order," but mistakenly identify the ungodly "disorder" in the world with the thermodynamic entropy. Certainly entropy is a factor in some of the world's "disorder," such as the degradation of the environment. But gravity, electromagnetism, and the 1st law are all involved as well, and there are no grounds for assigning any special "evil" role to the 2nd law. Calling the 2nd law evil because it is involved in, for example, the decay that accompanies physical death is as unfounded as calling gravity evil when somebody falls off a cliff.

Second, the physical evidence strongly indicates that, like all God's other physical laws, the 2nd law has been operating since creation. Entropic processes are involved in the burning of the Sun and other stars (many of which emitted the light we see today longer ago than the 6000-20,000 years ago usually assigned to the Fall), and would have been involved as Adam and Eve walked, ate and digested their food, etc. Assuming there were flowers in the garden, it is the 2nd law that allowed Adam and Eve to smell them (again speaking against the concept that entropy is inherently evil). While it is not impossible that God had an entirely different set of physical laws in place before the Fall, such speculation is not supported by any scientific or Biblical evidence.

Third, we need to deal with Romans 8.18-23, which talks about (in the context of the final fulfillment of the Kingdom) how "the creation itself will be set free from its bondage to decay and obtain the freedom of the glory of the children of God" (v. 21, NRSV). The "bondage to decay" is sometimes taken to refer to the 2nd law. That interpretation is at best incomplete. The Bible teaches (cf. Rev. 21) that, when all is said and done, God will renew creation into something that transcends all the limitations we now know. So while the "repeal" of the 2nd law may be a part of what the passage refers to, it is at most only a small portion of a much greater transformation. The "bondage to decay" seems in context to be more about lack of flourishing of God's creation in general due to human sin.

There may be an additional logical (and theological) fallacy at work in those who attribute the 2nd law to the Fall. The (faulty) line of reasoning goes something like, "Since the 2nd law will not exist in God's final Kingdom [that may or may not be the case], it must not have existed before the Fall." This simply does not follow. Nowhere in the Bible does it suggest that the final Kingdom will simply be a restoration to pre-Fall conditions. Instead, it is pictured as something brand new and infinitely more glorious than what Adam and Eve experienced in the Garden.

With all that said, I should add that I do believe that the Fall (whether interpreted as a singular event or as a metaphor for pervasive human sinfulness) has consequences. The primary result, of course, is our separation from God and need for salvation. But Scripture does teach (Gen. 3.17) that there are also negative consequences for our surroundings. I do not deny that, in some sense, the ground (and maybe even all of creation) is "cursed" because of our sin (I lean toward viewing that as our relationship to the environment being corrupted by sin). What I do deny is that the 2nd law of thermodynamics is any more a part of that curse than is gravity or any of the other physical laws God has crafted for His creation.

Final Thoughts

I used to think about entropy childishly. When I was about 20 and a fairly new Christian, I even wrote a poem called "The Second Law" in which I invoked entropy to explain decay of the human soul, of human society, and of Christ's church. [I later saw a "Life in Hell" cartoon listing "Entropy" as a topic about which all bad poets must eventually write.] Since then, I have learned more about thermodynamics and about God. I know how alluring the simplistic entropy arguments sound. But God calls us to truth, and that sometimes requires abandoning simplistic concepts.

My main purpose here is to dissuade my fellow followers of Christ from pursuing incorrect arguments based on a lack of understanding of the second law. One might ask whether it is really important for Christians to think about entropy in a mature manner. For many, it probably isn't. But for those who engage in apologetics, and for those who might find themselves defending the faith to those who are scientifically literate, I think it is important for three reasons.

The first is that, by abandoning these errors, we can focus more effectively on legitimate arguments for the faith. While I do not subscribe to the notion that one can arrive at Christianity through pure reason, I do believe that it is reasonable. With regard to origins, there are reasonable arguments that the universe and human life did not come about through random Godless chance. But none of these arguments is based on thermodynamics, and it can only confuse the issues and obscure God's truth when the 2nd law is inappropriately dragged in.

The second reason is the special responsibility to truth we have as people of God. There is no room for falsehood in God's kingdom, even in the defense of the Gospel. We should be diligent in our efforts to avoid bearing false witness, whether the victim is our next-door neighbor or Ludwig Boltzmann. Worldly politicians or marketers may say "I don't mind using a little falsehood as long as it helps persuade my audience," but that is unacceptable for a Christian. We who serve the God of truth should make a special effort to cleanse our words of all falsehood.

Finally, there is the Christian witness to the world. A small but not insignificant segment of the world is scientifically literate. It is tragic that many think of Christians only as "those people with the crackpot arguments about a young Earth and entropy" and do not even consider the Gospel because they think it requires them to believe things they know to be as silly as a flat Earth. The myth that Christianity is for stupid people is widespread, and part of the blame must rest on some Christians. This harm to our witness will only be overcome if Christians refocus their message on central truths (like the fact that God created everything) rather than trivial side issues (like how He did it), and repudiate those arguments (like the misuse of the 2nd law) that are simply incorrect. Many will still reject and belittle Christ and those who follow Him. But if the world is going to laugh at us, let it at least be for a central doctrine like the Cross or the Resurrection, or for our insistence on loving everybody, not for mistaken pseudoscientific arguments on peripheral issues.

Disclaimer: The views expressed in this essay are the opinion of the author of this essay alone and should not be taken to represent the views of any other person or organization.

Last major revision 2000. Page last modified October 16, 2018

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