Structure and Breakdown, Death and Decay
It is universal human experience that tools wear out, machines break down, and all living organisms die and decay. Many people confuse this tendency with the physical concept of entropy. Analogy is the only relation between the two. The second law of thermodynamics says nothing about the breakdown of structure.
Physicists can write no laws predicting when machines will break down, because some machines are made better than others. We must refer the question to engineers. They can test machines, analyze the reliability of the different parts, and predict the “mean time between failures,” how often breakdowns will occur. Their predictions do not set an absolute limit to the performance of individual machines.
Heat engines break down when their parts wear out or their tubes become clogged with scale and rust. The engines do not stop because their entropy becomes too large. The waste heat they exhaust into the environment carries away entropy. This allows the machines to maintain constant average internal entropy. They can continue working as long as they have fuel, sufficient working fluids, and adequate maintenance.
Entropy does not doom a star to destruction or extinction. The second law of thermodynamics says that entropy will increase in any reaction that emits heat. However, no law of physics limits how much fuel there may be. Some stars renew themselves for a time by drawing in hydrogen from clouds they encounter moving through space. In the 19th century people thought that the stars could only burn a few million years. This is because they only knew of chemical reactions. Such reactions can produce at most a few light photons for each atom that enters the reaction. But nuclear reactions can produce millions of light photons for every atom in the reaction. This 20th-century discovery, nuclear energy, has greatly increased the life expectancy of the stars. They have for a long time been burning a fuel we have only recently discovered.
Stars stop shining when they exhaust their fuel, not because their entropy becomes too great. Light and heat from stars carry much of their entropy away to the rest of the universe. The rest remains in the ashes. These sink down into the center of the star. Nuclear combustion continues in a spherical shell around the inert center as long as there is fuel.
The second law of thermodynamics does not doom living organisms to die, either. We can apply to our own bodies the above discussion about machines and stars. All living organisms maintain themselves in a state of low entropy by consuming food and expelling degraded matter. Telomeres, the terminators at the ends of DNA strands that keep the double helix from unraveling, get shorter and shorter as cells replicate. This presently sets the upper limit of human longevity. Actuaries can calculate average life expectancy sufficiently well to make the insurance business profitable, but not well enough so any individual may be certain of the date and time of his or her death. Mortality tables do not limit anyone’s longevity. The universality and irreversibility of death are not a consequence of the second law of thermodynamics.
The formulas engineers and actuaries use are not laws of physics. Such predictions are only statistical, not deterministic. Let’s note the contrast between statistical predictions and entropy. Entropy is calculable and measurable in controlled circumstances. Therefore entropy is not the same as wear and tear, breakdown, disease, death, and decay.
We can calculate entropy when there is some sort of structure, a gas in a box, a heat engine, or a string of coded symbols. The second law of thermodynamics is about how efficient the structure is in handling energy. The second law says nothing about the possible breakdown modes of the structure, or even if breakdown is inevitable. When physicists say that entropy is disorder, they mean a very specific measure of disorder, not general disorganization.
Physicists can write no laws predicting when machines will break down, because some machines are made better than others. We must refer the question to engineers. They can test machines, analyze the reliability of the different parts, and predict the “mean time between failures,” how often breakdowns will occur. Their predictions do not set an absolute limit to the performance of individual machines.
Heat engines break down when their parts wear out or their tubes become clogged with scale and rust. The engines do not stop because their entropy becomes too large. The waste heat they exhaust into the environment carries away entropy. This allows the machines to maintain constant average internal entropy. They can continue working as long as they have fuel, sufficient working fluids, and adequate maintenance.
Entropy does not doom a star to destruction or extinction. The second law of thermodynamics says that entropy will increase in any reaction that emits heat. However, no law of physics limits how much fuel there may be. Some stars renew themselves for a time by drawing in hydrogen from clouds they encounter moving through space. In the 19th century people thought that the stars could only burn a few million years. This is because they only knew of chemical reactions. Such reactions can produce at most a few light photons for each atom that enters the reaction. But nuclear reactions can produce millions of light photons for every atom in the reaction. This 20th-century discovery, nuclear energy, has greatly increased the life expectancy of the stars. They have for a long time been burning a fuel we have only recently discovered.
Stars stop shining when they exhaust their fuel, not because their entropy becomes too great. Light and heat from stars carry much of their entropy away to the rest of the universe. The rest remains in the ashes. These sink down into the center of the star. Nuclear combustion continues in a spherical shell around the inert center as long as there is fuel.
The second law of thermodynamics does not doom living organisms to die, either. We can apply to our own bodies the above discussion about machines and stars. All living organisms maintain themselves in a state of low entropy by consuming food and expelling degraded matter. Telomeres, the terminators at the ends of DNA strands that keep the double helix from unraveling, get shorter and shorter as cells replicate. This presently sets the upper limit of human longevity. Actuaries can calculate average life expectancy sufficiently well to make the insurance business profitable, but not well enough so any individual may be certain of the date and time of his or her death. Mortality tables do not limit anyone’s longevity. The universality and irreversibility of death are not a consequence of the second law of thermodynamics.
The formulas engineers and actuaries use are not laws of physics. Such predictions are only statistical, not deterministic. Let’s note the contrast between statistical predictions and entropy. Entropy is calculable and measurable in controlled circumstances. Therefore entropy is not the same as wear and tear, breakdown, disease, death, and decay.
We can calculate entropy when there is some sort of structure, a gas in a box, a heat engine, or a string of coded symbols. The second law of thermodynamics is about how efficient the structure is in handling energy. The second law says nothing about the possible breakdown modes of the structure, or even if breakdown is inevitable. When physicists say that entropy is disorder, they mean a very specific measure of disorder, not general disorganization.