Thesecond law of thermodynamicsstates that all energy-affected matter in the universe is becoming random. In other words, the totalentropy(S) in the universe is increasing. Entropy is defined as a measure of disorder. There is an important relationship between the movement of matter and the ordering of matter. All matter in the universe is tending toward disorder, however, systems can become ordered (become less entropic) with the input of energy.
How can any order be achieved if the tendency for matter in the universe is toward ever-increasing entropy? How can complex (and highly ordered) organisms exist at all? For that matter, how can there be any ordered states in the universe? The answer is that systems can become ordered as long as they are "open" to the universe.
Think of holding 10 marbles in your hand. Your hand represents a system consisting of 10 marbles. Now, turn your hand over and let gravity (a form of energy from outside the system) act on these marbles; they not only fall out of your hand (converting potential energy into kinetic energy), but they also become relatively disordered. You can reorder these marbles back into your hand, however, it requires the input of energy from outside of the system (i.e., your body as you walk around picking them up). The ordering of the marbles back into your hand is done at the expense of entropy somewhere else in the universe. Keep in mind that life (i.e., each organism) exists as a system that is open to the universe, and ultimately the energy that organisms obtain is used, in a sense, to reverse entropic change. From a thermodynamics standpoint, if you stop eating you will die because there is no input of energy from outside your body (i.e., your system) to reverse the natural tendency of matter to disorder. This figureis a summary of the second law of thermodynamics using a glucose molecule as a representation of a highly ordered system. The second law of thermodynamics favors the breakdown of the glucose molecule into CO2and H2O molecules.
The first and second laws are intimately related, and later you will learn how this relationship can be quantitatively stated. In a general sense, life channels energy thermodynamically (via a complex series of energy transformations) for the purpose of decreasing entropy (creating order). For the majority of life forms on Earth, this energy ultimately comes from the sun. Indeed, all the order you see around you is a direct result of the small fraction of total solar radiation that is absorbed by the our planet.
There is a special relationship between temperature and entropy. The entropic state of a given system is proportional to temperature. At absolute zero (in degrees Kelvin), the entropic state of any system is zero. Although absolute zero has never been achieved (-273 deg Centigrade), the relationship between temperature and entropy is important.