Why it doesn't contradict Christian faith
It is a fairly common assertion among some parts of the Christian church that the Second Law of Thermodynamics is the result of the Fall, in that it is thought to result in death and decay and a move from order to chaos. I want to defend this law of physics from being tarred as something not part of Gods intrinsically good Creation. Rather, I will then go further to explain why I see the Second Law to be an important part of that good Creation.
First, some basic thermodynamics. The Second Law can be stated in three equivalent ways: heat can never, of itself, flow from a lower to higher temperature state; it is impossible to extract heat from a reservoir and convert it to work without causing other changes in the Universe; any change in a closed system will always result in an entropy increase, and a change in a closed system can only occur if it's possible for entropy to increase.
It is the last of these that is often quoted when someone says it wasn't part of Gods' original design of the universe. This is because entropy is related to disorder, and increasing entropy increases disorder. The problem here is two fold; one is that the universe simply doesn't work without the Second Law (or at least not unless all the other laws of physics are different too) which would imply the Fall resulted in a complete recreation of the Universe. I'm not sure if anyone would seriously consider the Fall to have such an effect. I have no problem with God recreating the Universe such that it runs by different laws, although I'm not sure he necessarily will do so. I do have problems with the idea that the universe is not currently the way God intended it to be (in it's physical state, so excluding the spiritual, moral and relational problems humanity has).
The other problem I see is the idea that an increase in entropy is actually something bad. It is this second point that I'll concentrate on. Increasing entropy results in the potential for useful work to be done, it is one of the things that defines the arrow of time. The Second Law allows work to be done, for example the evolution of increasingly complex self-replicating organisms, albeit at the expense of increased disorder elsewhere in the Universe. The Universe and the laws that govern it's physical behaviour is well suited to developing intelligent beings (whether that has happened just once or many times) without God intervening in a miraculous way; I assume that that is part of the purpose of the universe within Gods plan for creation.
There is a conception that since ultimately the universe will end up in a state of maximum entropy that this somehow results in the universe being ultimately futile, which misplaces the purpose of the universe at it's end rather than in all the things that happen to get to that point. Why do some people seem to insist on assuming that the purpose of the universe is located at it's end rather than in what it produces along the way? Is there something inherently good about stability, or bad about disorder? Stability can easily lead to stagnation, but disorder can easily result in creative novelties. I'm much happier with the concept of a God who keeps stirring things up to cause new things to happen than one who settles for maintaining the status quo.
I believe that physical disease, death and decay have always been part of the created order. As such the Fall had no effect on the physical universe. It did, however, have extremely dramatic spiritual effects that resulted in spiritual disease, death and decay. I don't read the opening chapters of Genesis as a scientific account of Creation and Fall; it has far more important things to tell us than that. The story of the Fall is a description of the spiritual state of humanity, whether of not there was such a historical event. I believe it talks of spiritual death (ie seperation from God) rather than physical death, and the disease of sin that eats away at humanity individually and corportately. The breakdown of the relationships between people and God, people and the rest of creation and between people does, of course, have effects on the physical as well as spiritual.
The thoughts expressed here are drawn from a discussion which is archived on the Ship of Fools