Big Bang theory contradicts the second law of thermodynamics.
The reasoning behind such an assertion usually is that Big Bang theory posits a high degree of order in the initial state of the universe, but that the second law of thermodynamics forbids this.
The second law of thermodynamics states that the entropy of a closed system never decreases over time. This definition makes evident a number of problems with the creationist line of reasoning.
I. Entropy vs. disorder
As Lorenzo Benito has emphasized to me, it is important to be clear that the second law of thermodynamics deals with entropy rather than with "disorder." Although entropy often is described as a measure of disorder, only a very technical kind of disorder matches entropy; there is no rigid thermodynamic correlation between entropy and intuitive notions of disorder, such as the notions appealed to by conversational examples like shuffled decks of cards and messy rooms. For instance, the increase of entropy that occurs when a deck of cards is shuffled results not from the randomization of the card faces, but from the heat energy released by our muscles in the process shuffling. While there are reasons to expect shuffling to randomize cards, those reasons are not thermodynamic ones. John Pieper's talk.origins article Entropy, Disorder, and Life discusses in detail the limitations of the relationship between entropy and disorder.
It is not difficult to recast the creationist argument in terms of low and high entropy instead of order and disorder, but the modified argument still runs into problems, as described in the next points.
II. Entropy decreases in open systems
The creationist argument ignores the possibility that the universe is an open system. If the universe is, or ever was, part of a larger system (as hypothesized, for instance, by Smolin 1999, in which universes reproduce), it could have purchased its initial low entropy at the expense of increased entropy in the remainder of the larger system.
Some creationists insist that only open systems with some kind of sophisticated conversion mechanism in place can undergo a decrease in entropy. However, that claim is neither stipulated nor entailed by the second law of thermodynamics, and is in fact known to be false, as the examples of crystallization and endothermic reactions make clear. It is important to be attentive when presenting these examples to creationists, because many will respond by playing a shell game: they will reply that crystallization and endothermic reactions do not produce "complex information." But remember what the initial claim was: that the second law of thermodynamics rules out a decrease in entropy. That claim has been shown to be false. Anything creationists try to add to that about complex information being ruled out is a complete concoction by them, unrelated to the second law of thermodynamics.
III. What if the universe is a closed system?
If the universe is a closed system, a violation of the second law of thermodynamics would require that there be two distinct states of the universe, U and U*, with U preceding U*, for which U is of higher entropy than U*. But if we go by the equations of general relativity alone, then the origin of the universe was the origin of time itself), which means there could have not have been any state prior to the initial state of the universe, much less one with higher entropy than a subsequent state. This goes likewise for scenarios employing quantum gravity in which there was a first moment of time: for any cosmological model in which there is a first moment in time, the initial state of the universe can be of as low entropy as one wishes without violating the second law of thermodynamics.
Theories of quantum gravity that allow the universe to continue existing infinitely into the past are a different matter. It is unclear to me whether there is any way to reconcile them with the second law of thermodynamics, or whether they would require abrogation of the second law of thermodynamics.
Theories of quantum gravity that have time breaking down in the early universe are also difficult to assess, but since the second law of thermodynamics makes essential reference to time, it would seem that the second law of thermodynamics could not apply to such cosmological models at all.
IV. Expansion of a closed universe
Physicist Victor J. Stenger points out (2007: 117-121) that in an expanding universe, it actually is possible for the universe to start out in a state of maximal entropy, and yet for its entropy to increase over time, because the expansion of spacetime also raises the maximum allowable entropy. The maximum allowable entropy, in fact, increases faster than the actual entropy, which means that there is room for localized order to form.
Smolin L. 1999. The Life of the Cosmos. Oxford: Oxford University Press.
Stenger VJ. 2007. God: the Failed Hypothesis. Amherst, NY: Prometheus.
Last updated: 7 Mar 2017
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