SECOND LAW OF THERMODYNAMCS

Cosmic evolution stipulates that complexity arises from simplicity, or, we could say, order from chaos. Observations demonstrate that an entire hierarchy of structures has emerged, in turn, during the history of the Universe: energy, particles, atoms, galaxies, stars, planets, life, intelligence, and society. Yet this increase in complexity with the steady march of time bothers some people. Why? Because cosmic evolution, at face value, seems to violate the 2nd law of thermodynamics.

The 2nd law of thermodynamics is one of the most basic and cherished principles in all of physics. "Thermodynamics" means literally “movement of heat,” or more broadly interpreted, "change of energy." Its 1st law simply asserts that the total amount of energy is conserved (or kept the same) during any physical transaction; its 2nd law dictates that the total amount of randomness or disorder (technically called "entropy") increases during any such transaction. This is true because heat (i.e., thermal energy) always flows from hot objects to cold objects. And an inevitable result of this unilateral process is that a house of cards, once built, will tend to collapse eventually; by contrast, a random collection of playing cards is not likely to assemble itself into a structured "house." Similarly, water will of its own accord flow over a dam into a lake below, but has never been seen flowing back up to the top of the dam; eggs naturally crack open, but never reassemble themselves into a shell. These are classical examples of "closed systems" wherein events occur only in one direction. Nature is said to be irreversible or asymmetric.

However, Nature also displays occasional "open systems" whereby energy (and sometimes matter, too) flows into those systems from their external environments beyond. And this can make a great deal of difference (Figure 1.24). For example, a human being, by exerting some energy (and some patience, too, which also takes energy), can rebuild a house of cards. Likewise, a water pump (which also requires energy that also requires energy to run) could be used to transport water from a low-lying lake to above a high-lying dam.

FIGURE 1.24 FIGURE 1.24 – In an open system, energy (in the form of either energy or matter) can enter the system from the outside environment, thereby increasing the system’s total energy, enabling it to do work, and under some conditions become more complex. The symbols are energy E, heat loss Q, entropy S of both the system and the environment.

The infusion of energy into any system can potentially produce organized structures. Disorder (or entropy) can actually decrease within such open systems—which galaxies, stars, planets, and life forms are—even though that disorder is increasing everywhere else in the Universe. Such "islands of order" do not violate the 2nd law of thermodynamics because the net disorder of the system and its environment always increases. The energy needed to run a water pump—or any such device in our industrial civilization—comes at the expense of the environment that’s being ravaged to power our civilization; both digging for coal and burning it disorder the environment more than the order achieved by using that energy. Likewise, the energy exerted by humans to build a house of cards—or a table, chair, automobile, whatever—derives from the food we eat. We literally feed off our neighboring energy sources—locally plants and other animals, and more fundamentally the Sun.

For example, here's what happens in the food chain consisting of grass, grasshoppers, frogs, trout, and humans. According to the 2nd law, greater disorder mounts at every stage of the food chain. At each step of the living process, when the grasshopper eats the grass, the frog eats the grasshopper, the trout eats the frog, and so on, a toll is taken on the environment. The numbers of each species needed for the next higher species to continue decreasing entropy are staggering: To support one human being for a year requires some 300 trout, which, in turn, must consume 90,000 frogs. These frogs, yet in turn, devour 27 million grasshoppers, which live off some 1000 tons of grass. Thus, for a single human to remain "ordered" (namely, to remain alive) over the course of a single year, we need the energy equivalent of tens of millions of grasshoppers or about a million kilograms of grass.

To be sure, humans are heat engines that temporarily—for 70 years on average in the West—maintain order in our bodies by creating greater disorder in the environments surrounding us. Once we stop eating (or intaking energy), we die—whereupon we decay into disordered chaos. The same is true of a plant; if they stop acquiring energy via photosynthesis, they shrivel up and die. So is the case of a star, although they endure much longer, provided they process energy; during their formative stages, stars increasingly order themselves by utilizing energy and dumping entropy into their surroundings—and they continue to become ever-ordered during the course of stellar evolution. Eventually, after billions of years, stars too break down into disorder. In the end, the 2nd law always “wins,” but in the meantime we humans, among all open, ordered systems, can temporarily enjoy a rise in complexity with time.

In this way, any form of matter or life can construct and order itself by exchanging energy (and entropy) with the outside world. No laws of physics are violated, nor even circumvented. The evident order of the Universe around us does not at all contradict the basic principles of modern thermodynamics. These are the very principles that enable us to understand how both order can increase locally all the while disorder increases globally. The evident “constructiveness” of cosmic evolution is thus reconciled with the inherent “destructiveness” of modern thermodynamics.


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