The Heat Death of Civilization

The universe is gradually falling apart. Sometimes this is referred to as the "heat death" of the universe. Stars run out of fuel and disintegrate. Or, if massive enough, they blow themselves up in supernova explosions, strewing most of their matter into the surrounding space. New stars are being born, replacing the ones lost, but eventually the raw materials that make new stars will be exhausted. The remnants of fuel-exhausted stars - white dwarf stars, neutron stars, and black holes - will similarly die. White dwarfs will become cold, dense, Earth-sized cinders of carbon and oxygen. Neutron stars will be cold and lifeless lumps of city-sized nuclear matter. Even black holes will, over incredibly vast stretches of time, disintegrate into diffuse "Hawking radiation". It may not end there. If protons are ultimately unstable over those vast stretches of time, even the white dwarf and neutron star cinders will disappear. All that will be left is a universe of photons, growing colder and colder.

Why should this be? And why can't we arrest these processes? If we had sufficient technology, couldn't we just keep putting the pieces back together and continually restore the status quo? Stars convert hydrogen to helium (and other elements as they age) in their cores. When the hydrogen fuel got low in a star, we would just collect hydrogen from vast interstellar clouds and recharge the star. Or, cognizant of the fact this hydrogen, though vast, is not limitless, we might construct immense factories that reconvert the helium and other elements produced by stars back into hydrogen and use that to recharge aging stars. This would be recycling on a cosmic scale. The only problem is, it won't work, no matter how advanced the technology.

Although the statement, "it won't work", is bound to be aggravating to many a can-do-minded human, I'm afraid it's true. I once knew a handyman who was sure he could build a perfect refrigerator. He would use the heat generated by the refrigerator to run a dynamo that would then provide electricity to work the refrigerator. The energy would be continually cycled and the refrigerator would run indefinitely without being supplied with energy from an outside source. I tried to explain to him that there is the small matter of the second law of thermodynamics. I put it in as simple terms as I could, but it wasn't a lack of intelligence on his part that led him to reject my argument. He just didn't want to believe it couldn't be done. There had to be a way around this stupid law. Or, perhaps, physicists are just plain wrong.

Far from being "stupid", the second law of thermodynamics is one of the most profound concepts in physics. It is responsible for the continual change we see in ourselves and our surroundings. It is responsible for the continued integrity of our bodies, for the birth of new human bodies, for the evolution of life, and for the evolution of the entire universe. Pretty important stuff. The second law drives change. The nature of the change depends on the other laws of physics. This is such a powerful concept that some have claimed that the flow of time itself is a consequence of the second law of thermodynamics. You don't have to go that far, however, to realize, with this law, you have come into the presence of that which makes creation inevitable.

Well, you might think, why is a law that is the impetus behind change and creation responsible for the demise of the universe? That sounds like a contradiction, but the way the second law of thermodynamics creates (in concert with the other laws of physics) is by destroying. For every ounce of order created, there is a pound of dissolution, so to speak. A creative act at one place can only occur if a larger act of destruction occurs somewhere else. This allows for the appearance of order - creation - in the universe, but at a price - a big price - the ultimate price. The order can only be temporary. The universe must eventually "die" and break down into total disorder.

Recently, my daughter was in a high-school Christmas play, "Willy Wonka & the Chocolate Factory". She was only part of the chorus, but I think she did a good job. In this play, the hero, Charlie Bucket, happens to find a golden ticket in a Wonka chocolate bar. He opens the wrapper to find the ticket, strewing shreds of paper over the stage in so doing. Thus, Charlie, in increasing the order in his possession, decreases the order around him. It is much easier to tear the paper apart than to put it back together, so the disorder is greater than the order created. This is the essence of the second law of thermodynamics, and the cosmic significance of the strewn paper will hopefully become clear below.

You can look at the second law of thermodynamics from a merely "phenomenological" perspective. This means you observe what happens and make a generalization that doesn't include how it happens in terms of more fundamental processes. Say you see a number of processes where order decreases. You may then make the generalization that order always decreases. You see sugar cubes dissolve in a cup of hot tea. You never see a sweetened cup of tea produce a sugar cube. You acknowledge that the sugar dissolved in the tea is less ordered than the tea with the sugar cube intact. Therefore, you generalize that nature tends to greater disorder. Why, you don't know. All you know, or claim you know, is that it always happens that way.

But it apparently doesn't always happen that way. You place an ice-cube tray of water in the freezer and wait a couple of hours. When you open the freezer, you have a tray of ice cubes. You have learned that water is made up of molecules composed of two hydrogen atoms attached to an oxygen atom. In liquid water the molecules are (more or less) randomly distributed. (In actuality there is some short-range order in the way the molecules are distributed.) Solid water (ice), however, is highly organized as the molecules arrange themselves into a crystalline state with long-range order, sort of like house after house in a typical suburban subdivision. Isn't this the same, conceptually, as a sugar cube appearing out of a cup of sweetened tea? It looks as if order can arise from disorder after all. So much for the second law of thermodynamics!

The problem with this conclusion is that disorder has indeed increased as a result of the change of liquid water to ice. The water has increased its order by exporting disorder to its environment. And, when you take that disorder into account, it outweighs the order created. What does this disorder consist of? To freeze, the water has to give up a lot of heat. This heat does not involve a change in temperature. The water cools down to freezing (0° celsius, also expressed as 0° centigrade), but it doesn't cease giving off heat. It continues to give off heat (about 80 heat calories per gram) as its temperature remains steady but its order increases. Heat is disorder - a form of disorder that flows from higher to lower temperature. The water increases its order by giving off this heat as it freezes into ice at 0° celsius. In other words there is no temperature change as heat (disorder) is expelled to the freezer (the water's environment), and the liquid water gradually turns to ice, increasing the order of the water and decreasing the order in the freezer. When you measure the entire change, including not only the water turned to ice but also the heat given off, you find the total disorder has increased. So much for disrespecting the second law of thermodynamics!

The transfer of heat energy from a "system" to its environment is a way of exporting disorder. (A system can be pretty much anything consisting of interacting parts you choose, such as the molecules in a tray of water.) The freezing of the water in the above example involves other laws of physics, in particular, electrical forces. Without those forces, there would be no freezing of water to ice. (Which would be moot since, in the absence of electrical forces, there could be no water to freeze!) Without the second law of thermodynamics, you could put a tray of water in the freezer and wait until hell freezes over and still not get ice. (Of course, hell might not freeze either, for that matter.)

A consequence of the second law of thermodynamics is that spontaneous heat flow is from hot to cold and never the other way, since heat flow from hot to cold increases disorder as required by this law. Without this consequence, heat wouldn't flow only from the warmer water to the colder freezer air to produce the desired ice - it would just as likely flow the other way. You might instead get a tray of boiling water (however, this would be as unlikely as getting ice). Note this would not violate the first law of thermodynamics, which postulates the conservation of energy. The heat energy that flowed from the freezer to the water would be the same as that absorbed by the water so that no energy was created or destroyed as required by the conservation of energy.

A good physicist is never satisfied with a phenomenological observation. He or she wants to know how and why the process occurs. The physicist who gave deeper insight into the second law was Ludwig Boltzmann, who worked in the late 1800s. He believed in atomic theory - that all substances consist of atoms, or atoms combined into molecules (that is, consisting of particles that are either individual atoms or molecules). If that is true then there is an incredibly large number of ways these atoms, or molecules, can be organized with respect to each other. He made the assumption that, for a given total energy of the atoms, any of these ways, called microstates, are equally probable.

Consider the tray of water about to be placed into the freezer. It hardly matters to the person putting in the tray exactly where each of the water molecules is and how it is moving. Wherever they are, and whatever their individual motion in the water happens to be, the person sees a tray of water. This tray of water is termed a macrostate. A macrostate can consist of any of an incredibly large number of microstates. From one tiny fraction of a second to another, the tray of water will change from one microstate to another as the molecules jostle around. The tray of water has a certain temperature and a certain volume and is at atmospheric pressure (neglecting the very slight increase in pressure between the surface of the water and the bottom of the tray). The temperature, volume, and pressure determine the macrostate - what the person can measure or observe - and there is an incredibly large number of ways (microstates) the water molecules can arrange themselves, both in position and velocity, to render this particular macrostate.

It isn't hard to conclude that there is an incredibly larger number of disordered microsates than there are ordered microstates in a system. If all of these states are equally probable, than the likelyhood of a system being in a disordered state is incredibly greater than it being in an ordered state. This was what Boltzmann contended. As atoms or molecules (or even photons) randomly move around, they are far more likely to constitute a disordered rather than an ordered state. That is, it would take a mind-boggling stretch of improbability for the molecules of sugar in a cup of sweetened tea to move together and assemble themselves, by accident, into a cube. This implies that the second law of thermodynamics is, in some sense, not a real law of physics, but a statement of probability given that the universe is made up of particles - atoms, molecules, ions, photons, etc. - in constant and random motion.

Except the motion is not entirely random. Forces such as gravity and electricity cause particles to move in non-random ways. Nevertheless, there is a tremendous amount of randomness at work. Enough randomness that, on the whole, order decreases with time.

Moving on from a golden ticket in a Wonka chocolate bar and a tray of water, consider a gold atom. Now, this particular atom was recently synthesized in some sort of nuclear reaction, possibly as a result of a supernova explosion, and is soaring through mostly empty space. Mostly empty, that is, but for a proton with which it has a chance collision. The collision adds energy to the gold atom, putting it in what physicists call an excited state. This means one or more electrons in the atom have more energy than they would have in their lowest energy states. There are possibly several microstates available to the excited gold atom, all with the same energy. However, there are fantastically more microstates consisting of the gold atom back in its lowest energy state (the so-called ground state) and a photon (one or more) moving away from the atom, carrying off the extra energy. The number of these states is huge, because a photon can leave the atom in any direction whatsoever. If all microstates are equally likely, there is a much greater probability the excited gold atom will transition into an unexcited atom by emitting one or more photons. Of course, there are other laws of physics involved in this process, in particular electrical forces and quantum mechanics.

A process like this, where a system (here, the excited gold atom) "seeks" its lowest energy state is often referred to by saying, "Nature is lazy. It wants to be in the lowest energy state possible." However, the new state, unexcited gold plus photon(s), has the same energy as the excited gold atom. The conservation of energy says that nature will always have the same total energy. What has really happened is that the laws of probability have led to a more disordered situation. The second law of thermodynamics guarantees that a system, unaffected by its environment, will evolve to the state of greatest possible disorder. So, Mother Nature is not lazy, just messy.

But then you look around. Biologically, nature is complicated and ordered almost beyond belief. You see organisms with incredibly complex bodies. You see very complex plant and animal communities maintain, and even increase, their complexity. You see the ecological balance that maintains the order of vast ecosystems. You explore the past by studying fossil life and discover that, on the whole, biological complexity on the Earth has increased over time. So much for the second law of thermodynamics!

Creationists will contend that the second law of thermodynamics proves evolution could not have occurred. On the contrary, the second law of thermodynamics does not prevent the accumulation of biological order on Earth so long as there is a greater increase of disorder elsewhere. But where is this disorder? It isn't under the sea. It isn't in the atmosphere. It isn't in the solid Earth. So, where is it?

Life is truly incredible in its ability to export disorder. This is like the tray of freezing water but "infinitely" more complex. How does the tray of water export disorder? Recall it is through giving up heat to its environment. The biosphere (the sum of all life on Earth) does exactly the same thing. Where does this disorder go? Ultimately, to space. Biological processes produce heat. This heat raises the temperature of the Earth just the tiniest amount, increasing the heat flow to space. Heat, you may remember, must flow from high to low temperature and is a flow of disorder. In the case of the Earth, the flow of heat to space occurs by the emission of heat radiation (that is, thermal infrared radiation such as that you feel emitted by a hot fire in a more intense form). This heat flow exports disorder to space allowing life to be ordered on Earth. Again, the second law of thermodynamics triumphs!

The details of this process are still being unraveled by scientists. After all, nature has had billions of years of trial and error to produce the ordering processes we observe, and we have just started, really, to figure all this out. Nature uses the laws of physics to create chemistry. Then she uses a particular chemistry, biochemistry, to create life. How this all has happened is a great mystery that is gradually being revealed by science. We have made great strides, such as the mapping of the human genome and the genomes of many other species. We are learning about the thousands and thousands of biological molecules and how they interact. But we are still scratching the surface. The second law of thermodynamics, however, doesn't care how the ordering is done, so long as if it is done, it is done at someone else's expense. In the case of the Earth's biosphere, the unlucky recipient of our disorder is outer space.

The biosphere is an almost impossible highly ordered state of matter. Yet its order is actually quantifiable, as is the disorder thrown out into space. To quantify disorder, you must have some sort of way of measuring and computing it. This is what the scientists Rudolf Clausius and Ludwig Boltzmann of the nineteenth century did. They each came up with a formula to quantify disorder. Even though these formulas appear to be totally different, they actually calculate the same thing. The measure of disorder is called entropy.

Let's look at Clausius' formula. According to this formula, the rate of the export of disorder with time (the time rate of the flow of entropy from a system to its environment) can be expressed as the heat flow from the system to its environment divided by the absolute (kelvin) temperature of the environment. (The kelvin temperature scale, named after the British scientist of the 19th century, Lord Kelvin, uses the same degrees as celsius, but takes zero temperature to be absolute zero rather than the freezing point of water.) In general, for an environment whose temperature is changing, you have to divide the heat flow at each temperature and add these all up. However, if the environment maintains a constant temperature, you can simply divide the total heat flow by that constant temperature. This is true for the tray of freezing water in the freezer, assuming the freezer temperature remains constant at about 0° C, or 273 kelvin (written in scientific notation as 273 K).

Let's say it takes exactly one hour for the water to freeze. During this time each gram of water gives up about 80 heat calories, which comes to a heat flow rate of about 0.022 heat calories per second. We need to change our heat energy flow units to watts if we want to express the flow of disorder in scientific units, watts per kelvin (the same as "entropy per second"). The heat flow comes to 0.093 watts (0.093 W) so that the rate of disorder (the rate of entropy flow) exported by the freezing water is 0.093 W divided by 273 K (the freezing point of water in kelvin), or about 0.00034 watts per kelvin (W/K) for each gram of water. Multiply this by the number of grams of water in the tray (say 200 grams), and you get the total rate of the loss of disorder by the water, 0.068 W/K in this case. Multiply again by the number of seconds in an hour and you get the total entropy that the water has lost in units of joules (J) per kelvin. (A joule is an energy unit equal to the amount of energy in a flow of one watt in a time of one second. Therefore a 60-W bulb will use 60 J of energy every second.) The disorder lost by the water is therefore about 250 J/K. If the freezer temperature is, say, 10 K lower than the freezing point, 263 K, then the disorder gained by the freezer will be, performing a similar calculation to that above, about 260 J/K. Note that, as the second law of thermodynamics demands, the total change in disorder, water plus freezer, is 260 J/K minus 250 J/K or 10 J/K. Order has decreased for the system as a whole, as required by the second law.

It is more daunting to apply this formula to the biosphere. However, you can make a "back of the envelope" approximation that should at least give you an idea of the magnitude of the disorder exported to space. You need the heat flow of the biosphere to its environment (and ultimately to space) and an approximate average temperature of the biosphere's surroundings. The latter is fairly easy to estimate - a reasonable choice is 300 K (80° F). The former is harder. The biosphere gets energy from photosynthesis, originally in the form of sugars, but gives off heat as it uses this energy to maintain its integrity. You have to calculate the heat generated by the biosphere in using the energy provided by photosynthesis and then divide by 300 K to get an estimate of the disorder the biosphere exports to its environment.

A little research turns up some numbers you need to compute the amount of heat given off by biosphere. The average amount of solar radiation falling on the lighted side of the Earth is about 600 watts per square meter, adjusted to account for reflection by clouds and absorption by the atmosphere . (A meter is a little longer than a yard.) The area of the lighted disk of the Earth comes from the formula for the area of a circle with a radius equal to that of the Earth. Therefore we find that about 80 thousand trillion watts of solar power fall on the Earth's surface.

How much of this 80 thousand trillion watts is intercepted by photosynthetic organisms? The Earth consists of about 30% land, and although there are photosynthetic plankton in the ocean, most of the ocean is a biological desert. There are vast stretches of land that are desert or covered by ice. In addition a lot of the light from the sun comes in at too low an angle to support photosynthesis, so I make a reasonable guess that something like 10% of the sunlight is actually intercepted by photosynthetic organisms. (This is just an "order of magnitude" calculation, after all.) That would mean about 8 thousand trillion watts of sunlight is available to make sugar and oxygen out of carbon dioxide and water, which is what photosynthesis does. But not all of this sunlight can be used to do this; only about half the photons have the correct energy, and only a fraction of these are absorbed to make sugar. Estimates are that only about 3% of solar radiation energy is actually stored. So, about 2 hundred trillion watts are continually being stored in sugar worldwide.

A small fraction of this energy is sequestered in sediments to form, for example, fossil fuels such as oil and coal. However, it is clear that the vast majority of it ultimately is released back into the environment as organisms die, decay and turn back into carbon dioxide and water. To a very good approximation, the rate of disorder being exported to space by this decay should be, according to the formula produced by Clausius, the rate of energy released by decay (approximately equal to the rate of energy stored by photosynthesis) divided by 300 kelvin. This amounts to roughly 800 billion watts per kelvin.

That's a really huge number - the amount of disorder the biosphere has to get rid of to maintain itself, but what does it mean? How can you put it in perspective? Well, you can compare it to the amount of disorder human beings export to the environment (not including that due to metabolism, which is part of the biosphere already computed). This is pretty easy to compute, since a brief Internet search turns up the fact humans used about 15 trillion watts of power in 2008. With an environment temperature again estimated at 300 K, this amounts to an outward flow of disorder around 6% of that exported by nature. It is amazing - or maybe not so much, given our impact on the environment - that humans are producing numbers that can be compared with nature.

This energy consumption by both humans and nature will, once again according to the second law of thermodynamics, raise the Earth's temperature. (I am not talking about greenhouse gases here, which is another matter.) A calculation I won't afflict you with shows this change in temperature to be negligible: only about one-tenth of a degree celsius for nature and about six one-thousandths of a degree celsius for humans. The difference between nature and humans is that nature uses energy from the sun that would go to heat the planet anyway, so no net temperature change occurs. Humans mostly use fossil fuels, so this energy is extra, although, as we see, quite negligible. The non-negligible effect of greenhouse gases, on the other hand, is not due to extra energy but to how they change the flow of heat already in the atmosphere.

Let's return to the golden ticket and the gold atom for a minute. The gold atom, like the biosphere, exports disorder by radiation. Both the biosphere and the tray of water in the freezer export disorder by giving off heat (as would a warm gold nugget composed of innumerable randomly excited gold atoms - the radiation has to be random to be heat). However, the torn wrapper strewn over the floor of the stage, although an increase in disorder, involves no apparent heat flow. In other words, here we have disorder produced that does not (unambiguously) involve heat flowing from a hot to a cold system. This type of disordering process is not described conceptually by Clausius' formula. We must, instead, look to Ludwig Boltzmann, whose formula approaches the idea of disorder from the point of view of how matter (or, more precisely, states of matter) is arranged rather than heat flow per se.

You are a prospector looking for gold. You come upon a hill composed completely of quartz sand grains, all identical, except for thousands of gold nuggets randomly distributed throughout the sand. Naturally, this is not how gold is found but assume this scenario for simplicity. After you stake your claim, you wander over the sand hill, picking up a gold nugget now and then as you find it. This is a slow process, and you know you'll never get the buried nuggets this way, so you have an idea. You will resort to hydraulic mining, where you use a high pressure hose to gradually wear down the hill. The sand and nuggets will be directed down a sluice where you will use the difference in density between quartz and gold to separate the gold from the sand. The sand will be flushed down a local stream, and you will eventually have all the gold nuggets in your possession. You will have increased the order of the gold nuggets. Once they were randomly mixed in with the sand, but now they are all in your deposit boxes. You have become incredibly wealthy, but at what cost? What price has the second law of thermodynamics exacted?

To find out we turn to the Boltzmann formula. Boltzmann's idea of disorder goes like this. You have a carton of twelve milk bottles. One half of the carton contains six bottles of chocolate milk and the other six of whole milk. The bottles of chocolate milk are all identical, as are those of whole milk. Since the bottles are identical, you can interchange any bottle of chocolate milk with any other such bottle, and everything looks the same; you can't tell any difference. The same holds for the whole milk.

Your carton is in a highly ordered microstate. Since you can't tell any difference when you switch like bottles, the microstate stays the same. If you have a symmetrical carton (say, three by four bottle containers), you can switch every chocolate bottle with every whole-milk bottle and get a second ordered microstate, so you actually have two ordered microstates, defined as bottles on either side of the carton being the same kind. Things will look different, however, if you switch any whole milk bottle with a chocolate bottle. The mathematics of probability say that there are 924 distinct ways you can do this, meaning you now have the two ordered microstates plus 922 others where there is at least some disorder. If you were to take the bottles out of the carton, have someone mix them around with your eyes blindfolded so you didn't know which bottle was which, and then put the bottles back into the carton with the blindfold still on, chances would be only one in 462 that you would achieve one of the two ordered microstates. Note there is no obvious heat flow here, and yet, just as the second law demands, order has almost certainly decreased by your random blindfolded work. The more bottles and cartons, the smaller the chance you will get an ordered result. With two cartons and 24 bottles, for example, the chance of getting an ordered microstate where there are twelve chocolate bottles in one carton and twelve whole-milk bottles in the other, would be less than one in one million. Well over a million microstates would be mixed and only two ordered.

Let's consider what this means back at the gold mine. You created the order of the gold nuggets at the expense of greatly disordering the sand and the environment. There is an enormous number of ways the sand could end up downstream, plus the action of the moving sand would create even more disorder. The environmental damage could be huge. And it was in California when hydraulic mining was used during the Gold Rush. Sediments from the mining filled rivers, leading to devastating floods, severely damaging both farms and cities. River navigation was severely impacted. Large numbers of trees were felled for fuel, adding to the devastated landscape eroded by high pressure water. The practice of using mercury to separate gold from the rest of the mined material led to downstream contamination, especially in San Francisco Bay, such that the consequences of the mining continue to this day.

Of course, the gold miners didn't intend to cause this much devastation; they just wanted to be wealthy. This and other environmental disasters show that the second law of thermodynamics is the mother of "the law of unintended consequences". Not just inanimate objects such as gold and sand are subject to the second law and its daughter law, but people as well, including all their activities. And not just the environment may suffer but humans and their institutions. The second law of thermodynamics knows no boundary.

Stand back a bit and look out how nature works versus how humans usually do. The biosphere does not permanently disorder matter. Instead, it recycles it. Carbon dioxide and water are combined by photosynthesis to form sugar and oxygen. The sugars and oxygen go to power the biosphere, providing energy to other organisms - energy to consume other elements necessary for life, to fabricate new biomolecules, to repair damage and wear to maintain body integrity, and to propagate the species. Ultimately, all (or almost all) this biological material that is fabricated turns once again into carbon dioxide and water and the trace elements used by living things. Nearly all the energy captured by photosynthesis is turned into disordered energy (heat) and ultimately expelled to space. Nearly all the matter is recycled, from disorder in the environment, to order in organisms, and back to disorder in the environment, and so on. This recycling is powered by energy captured from the sun. If nature didn't maintain itself this way, disorder would inevitably build up on the Earth, and life could not sustain itself.

As you know, this is not how we humans do business. We only get a fraction of our energy from so-called renewable sources - ultimately, these are all from the Sun. It is perhaps ironic that fossil fuels, from which most of our energy comes, contain stored solar energy. (You have a solar-powered car but may not realize it.) As far as the second law of thermodynamics goes, this energy is not a problem, because, like the energy used by the biosphere, it all eventually goes out into space as thermal radiation. Now, there may be a local problem due to, for example, hot water from a power plant being discharged into a stream, but globally everything is copasetic.

The real problem is how we humans create disorder in matter. We have landfills and human wastes, mine tailings, carbon dioxide and other greenhouse gases in the atmosphere, smog, trash in the oceans and on beaches and roadsides, pesticides and other chemicals in waters both above and below the Earth's surface, nuclear wastes, cleared lands, and on and on. All this is disordered matter. It is perhaps impossible to put a number on the amount of this disorder, but it certainly must be about the same order of magnitude as our heat disorder, which you recall was 6% of nature's. Nature's recycling mechanisms have been able to handle a lot of it, so long as it (like human biological waste but not plastic waste) is "natural", but nature is gradually being overwhelmed by the concentration of waste produced by humans. (The Gulf of Mexico oil spill is an extreme example of this. There are natural oil seeps in the sea floor of the Gulf, but they don't overwhelm the natural processes that convert them into compounds like carbon dioxide that can be used in the biosphere.)

Nature, undisturbed by humans, can maintain itself indefinitely, but neither nature nor we can maintain our current course. The second law of thermodynamics says so and we better take heed. With population growth, technology advancements, and rising standards of living, the amount of disordered matter exported to the environment will grow. How much can nature take? Well, she isn't handling what we are already dishing out all that well. Species are disappearing at rates only seen during "mass extinctions" in the fossil record. The ocean is acidifying. The climate appears to be changing. We cannot continue to increase disorder on our planet and survive. Disorder is the same as unavailable energy, and we need energy to live. If things continue as they are, a breakdown is inevitable. It may not be in my or your lifetime, but it will happen.

So, what do we do about this? The obvious solution is to behave like nature: get all of our energy from the Sun and recycle all our material. The problem is that solar energy is very diffuse and already contains a high degree of disorder. This is one reason why only 3 to 6% of it is captured by photosynthesis. Then, if we really do begin to recycle everything, we will need more energy than we are now using. We can, of course, be as efficient as possible, but there is a limit, again enforced by the second law of thermodynamics, to how great that efficiency can be. It can certainly never be greater than 100%, and the Carnot cycle, a consequence of the first and second laws of thermodynamics, says it can't even reach that. (The Carnot cycle usually gives unrealistically high efficiencies. For example, the Carnot cycle says that the maximum efficiency of photosynthesis is 95%, but the actual efficiency, due to factors mentioned above, is only about 0.25%.)

At some point it will be too late. There will be too many people and too much demand on our planet. The future does look pretty gloomy without some form of abundant and clean energy. Solar energy is an unlikely source. Recall that 80 thousand trillion watts of solar power strike the Earth. (Included in this is the energy it takes to drive the weather, meaning wind energy is also part of this.) However, even photosynthesis can only harvest 200 trillion watts. We humans now use more than 15 trillion watts, 7.5% (!) of what nature needs. In a "perfect" world, every person on Earth would have an economic condition equivalent to the average American. How much energy would be needed?

According to the Department of Energy, each American consumed over ten thousand watts in 2008. Spread that out over a population of six billion people, and we would need 60 trillion watts. This is over one fourth of what nature gets from the Sun! Solar power doesn't seem to measure up to the needs of humanity. On the other hand, if we were to divide the current energy use equally, each person would get only about one-fourth the energy an average American consumes. How would you like your standard of living to be one-fourth of what it is now? Improving technology can help - increased efficiency, life-cycle engineering and management of our consumer goods, improved energy generation and storage, new materials, and so on - but only if the technology takes the second law of thermodynamics into account. And the cost will go up as we will have to pay, not only for the goods, but the recycling costs as well. At the moment too many industries, institutions, and individuals dump this cost on someone else (typically on local, state, or federal government aka "the taxpayer") or on the biosphere. The biosphere has to handle its own mess and can't handle our growing mess as well.

What energy sources can we tap, if not just the Sun? The unfortunate fact is that any energy generation is subject to the second law of thermodynamics, even photosynthesis, as we have seen. The more energy that is generated, the more disorder that will also be generated. To counter this, our energy sources need to be as efficient as possible and to ultimately generate disorder in the form of heat rather than disordered matter if we are not to choke on our own garbage. Heat can be expelled into space, unlike human-generated carbon dioxide.

As a relatively clean source of energy, nuclear power comes to mind. It generates mostly heat and relatively little waste compared to fossil fuels. The most efficient nuclear fission plants are the breeder reactors, but their use is problematic due to proliferation concerns. They generate nuclear "waste" that can be reprocessed to extract the plutonium, which can be used as fuel. The problem is the danger of diversion of plutonium to nuclear weapons. This danger might be avoided by a design where the nuclear material stays in the reactor and does not need to be removed for reprocessing. A major advantage of breeder reactors is that the nuclear waste ultimately produced only takes a couple of hundred years, more or less, to lose nearly all of its radioactivity. Nuclear waste produced by most of today's reactors will stay dangerous for many thousands of years.

Thought to be even more efficient are nuclear fusion reactors. These should generate even less waste material than fission reactors, and the supply of fuel - deuterium from sea water - is practically endless. Contrast this to the need for uranium and/or thorium mining to supply fission plants with fuel. The problem is fusion power is decades off. The international ITER project, now underway, which will try to build a sort of prototype reactor, should clarify just what scientists and engineers have to overcome to design a production reactor.

As more humans inhabit the planet and as (we hope) their standards of living rise, we are facing the danger of increasing the disorder on the planet to the point it may become, ironically enough, essentially unlivable. The most dangerous disorder we create is disordered matter, which often has unintended consequences, such as the deterioration of the ozone layer due to man-made chemicals, damaging floods due to unwise water projects and urbanization, floods and devastating mudslides caused by deforestation, ground subsidence resulting from groundwater and oil and gas removal, chemical and pesticide pollution (witness the environmental crisis due to the use of DDT), growing "dead zones" in the seas due to agricultural run-off, just to name a few. Very worrisome is the increase of human-generated gases in the atmosphere. Methane and carbon dioxide (and some even more powerful but less abundant "greenhouse gases") threaten to change the climate. Carbon dioxide also dissolves in sea water and increases the acid in the ocean. Just as worrisome is the current global mass extinction of species that seems to be the result of human-produced habitat loss.

The only practical way to minimize matter disorder is by conservation, recycling, and turning to energy sources that produce disorder in the form of heat rather than disordered matter. We really don't have an energy crisis, if you look at our situation in light of the first two laws of thermodynamics. The first law says you will always have the same amount of energy in the universe. The problem is how much usable energy you have, and that is determined by the second law of thermodynamics. What we actually have is a usable energy crisis, not an energy crisis per se.

To get in step with the second law of thermodynamics, we are going to have to do some things. Don't forget, this is a law of nature. Congress cannot repeal it; treaties cannot do away with it. It will take "cleaner" energy sources (in the sense of producing less disordered matter), conservation, increased efficiency (recall the second law of thermodynamics puts limits on this, however), recycling, and life-cycle-engineered products (a sort of "crade-to-grave" plan to minimize impact on the environment). In short, it will take a radical departure from the way we are currently doing business. It's a matter of survival.