Two of the most important breakthroughs in science became prominent during the nineteenth century. One in the science of physics was the establishment of thermodynamics or the field of physics that studies energy and how energy changes from one form to another. Thermodynamics consists of two well known laws, the conservation of energy or the first law and the law of increasing entropy or the second law. The first law states that energy or the ability to do useful work can be converted into other different forms of energy: Energy cannot come from nothing and it cannot disappear. Energy can only change form so in principle of all the energy in the universe that is present other forms of energy can be converted perhaps into forms useful for human welfare. But not so fast! There is another law, the second law which states that there is a quality of energy called entropy. What is entropy? In the first law, it talks about quantity where for any system or a region of space where there is a given amount of energy and the science of thermodynamics was founded on the study of such systems , and these kind of systems are what is called isolated systems or systems where nothing can enter and nothing can leave. From the study of ideal systems based on actual experimental work, energy can be converted into different forms. If the first law dealt with quantity then the second law or the law of increasing entropy is the opposite; entropy is about the quality of energy. In the study of the same kind of systems, it was found that energy can be converted into one form of energy, heat, which is actually a disordered form of energy and entropy measures the amount of that kind of energy that is disordered or energy that cannot be used to do any work so the second law as was formulated during the nineteenth century states that for any process that converts energy, entropy or the unavailability to do useful work increases. In other words entropy increases until equilibrium or the state where nothing really happens is achieved. The second law states that entropy increases until it reaches a maximum amount so in a isolated system the amount of entropy is low but as time progresses the entropy becomes large or the future of the system is different than in the past and indeed entropy measures what scientists call the arrow of time: the flow of time can be characterized by the increase in entropy or that there was less entropy in the past than there is in the future.
Another way to measure entropy is to consider matter at the molecular level. Matter consists of atoms and molecules and a system such as ice, has a definite pattern of water molecules are locked into an ordered crystalline structure. Since the molecules are moving very little, entropy can be considered the measure of order at the molecular level but when ice melts, all the molecules are free to move around and so entropy of the ice becomes larger. Entropy based on the definition of how atoms are arranged in systems reflects a degree of order. Order can go into disorder and the more the molecules move into all directions in space or when water becomes steam, the more disorderly the molecules are arranged which is different than when the same molecules were compacted together into ice, the more the entropy increases. Another definition of entropy is that it measures the degree of molecular disorder; the higher the disorder the higher the entropy. To sum it up, the first law deals with the quantity of energy while the second law talks about increasing entropy or increasing disorder or that the quality of energy that can do work decreases so order runs into disorder.
Another breakthrough occurred in science, notably biology and that is the theory of evolution by natural selection as outlined by Charles Darwin’s well known work The Origin of Species. All of life has a common ancestor, argued by Darwin and based on evidence that Darwin collected from his voyage to the Galapagos all to colloborations with other naturalists and based on his work in various fields such as paleontology, animal and plant breeding, animal behavior, taxonomy, and biogeography or the study of the distribution of living things, Darwin concluded that evolution or “descent with modification” is inevitable because of three observations for populations of organisms whether they are animals, plants, fungi, and microbes. Populations of organisms in any environment small or large are growing because of absence of predators and presence of food and populations but predators are present and food is limited so populations cannot grow faster than the resources needed to support them so in each organism that can produce far more offspring, only few will survive. Those surviving few will compete with one another and through competition only those with certain traits such as the ability to see better, to run away from predators, and so on will have an advantage compared to those individuals without such traits who will have no such advantage and the ones that do will survive and passed on their advantageous traits to their offspring. Because this is occurring in their environment it is apparent that the environment is selecting those individuals that can survive and it is this mechanism that Darwin recognized as natural selection which in comparison to animal and plant breeding or “artificial selection” where humans have been selecting desireable qualities such as thicker coats or fleshier fruits and allowing those useful qualities to pass on to future generations. Natural selection works on the surface as well as in the inside of each organism and that would make the difference between survival or death. Gradually as Darwin inferred and later proven to be correct, a population can evolve into new species even into several species resulting in new and distinct species that are completely different from the ancestral population.
Biological evolution more or less is about the increase in order such as various species with survival conferring traits that was not present in the previous populations. You may notice a paradox and indeed there is a paradox that some scientists noted. If according to the laws of thermodynamics the universe is increasing in disorder then how is life possible and if life evolves into new species with new individuals would that be an increase of order? Order increases with order in the biological world that much is true but life coexists with the physical universe which is increasing disorder so the paradox is : How is life possible in a universe where disorder increases? Is life violating the second law of thermodynamics? Indeed at first glance when you look at how intricate a flower is or when you study the inside of an eukaryotic cell, you cannot escape the fact that these are complex systems and even more so when these organisms reproduce they are almost exactly like there parents although there will be some differences, however slight, that according to Darwin will allow the offspring to survive or perish. There was once a belief called vitalism where it was thought that there was some magic quality to life which endowed it with properties such as growth and reproduction perhaps even the ability to break the second law, but we know that organisms are composed of the same atoms as non living substances; its just that the atoms are arranged in organisms more differently than in inanimate systems.
How is it possible that life can become complex when the universe increases entropy? Recall that thermodynamics was founded on what was called isolated systems or systems that do not allow energy and matter to go in and to come out. From the studies of isolated systems it was found that entropy increases until a maximum amount is achieved and no further changes result. Notice that only isolated systems were first studied but are there are other systems to consider? Yes, and there are open systems and as the name suggests these are systems where matter and energy goes in and matter and energy goes out. In regards to the second law if open systems are considered then we would have to broadened the second law to consider entropy of the system and its environment and in the past 50 years a much more general form of thermodynamics , non equilibrium thermodynamics or NET for short studies systems that are open and away from thermal equilibriums and it turns out that open systems are real while isolated systems are really just ideal systems and with the study of NET it becomes possible to solve the paradox: How is biological evolution possible if entropy increases?
Recall the example with the ice cube. Atoms are arranged in a pattern but entropy is still present. That kind of entropy is low or negative entropy and negative entropy corresponds to a high degree of order but if heat flows into ice cubes, the molecules possese so much energy that there is more movement and so entropy goes from negative to positive. This is based on the fact that the ice cube is part of an open system where heat flows in and heat can flow out. This is contrast to an isolated system where no energy can come in and no energy can go out.
What about living systems? Suppose you grew a batch of E.coli all of which are capable of metabolism and reproduction but you place all the E.coli in a isolated system and no fresh nutrients are allowed to enter the population and no wastes can exist. After some time, all the cells will cease metabolizing and reproducing because the cells will be in an isolated systems and all cells of E.coli will approach thermal equilibrium and every molecule of E.coli will be in a state of maximum entropy and no further biochemical activity is possible or in other words all the E.coli will be dead.
If the grown batch of E.coli is allowed to be in an open system where nutrients are added and wastes are removed and as long as there is a flow of nutrients in and wastes out, populations of E.coli can continue to metabolize, reproduce even evolve into new strains and that is because of the fact that those cells are in an open system. A bacterium of E.coli if you could look at one at higher magnification is composed of several polymers; a cell consists of cell membranes and cell wall, there are protein and RNA structures called ribosomes where genetic information is translated into proteins using amino acids present in the cytoplasm of each cell bounded by membranes that cover the entire length of the cell and there are DNA molecules where the information for the structure and function of the cell is located. Protein molecules called enzymes which speed up biochemical reactions and are vital from breaking down molecules to forming molecules and forming molecules takes energy. Energy released from metabolizing molecules is stored in a molecule called ATP and when ATP is broken down energy is released and that released energy is what allows molecules to come together in cells whether they are cell membranes to replicating DNA molecules.
You can see that a cell is a system of interacting molecules each performing various functions and through this complex system of interaction more complex than the simple system of water molecules making up the ice cube, the processes of life ranging from protein synthesis, movement towards food, and reproducing. The cell does something in order to make a living and this is made possible by the fact that the cell is a open system and that a living thing is a part of the environment and to live is to depend on flow of energy and matter and to release wastes into the environment. As long as there is flow of energy, living cells whether unicellular organisms to multicellular organisms will continue to grow and evolve and each cell has a very high degree of order, or a large amount of negative entropy while the entropy of the environment is increasing slowly into disorder.
The paradox between order and disorder disappears when you consider opens systems but open systems are a part of the larger environment, and entropy in open systems can increase, go to zero, or decrease and order can increase in open systems as long as there is a compensating increase of entropy to the environment. When order increases in open systems, disorder of the environment increases so the second law is not violated in the least.
The gist of NET is that systems that are from from equilibrium tend to decrease in entropy along with a corresponding increase in order and that is because those systems tend to be open and as order increases disorder increases outside. Life is no exception to this and it because of the flow of energy and since the biosphere or the sphere of life is possible because of the flow of energy in the form of visible light and is used in that biochemical process known as photosynthesis and oxygen is released which is used by animals for respiration which in combination with glucose, carbon dioxide, water, and heat is released and the carbon dioxide is then reused by all green plants, algae, and cyanobacteria through the process of photosynthesis where oxygen is released as waste and glucose is synthesized while infrared energy is released into space. With biological order evolution is inevitable and with open systems such as the biosphere, evolution of life forms with their ability to take in food as a source of energy and through metabolism , energy can be used for reproduction and through reproduction evolution by natural selection is inevitable, and as long as the environment is considered the second law is maintained with the open systems that is life with its ability to take in energy and matter, cycle matter, convert the energy into many useful forms or more simply it is because of the second law of thermodynamics that life is possible.
Atkins, P (2007) Four Laws that Drive the Universe. Oxford, England: Oxford University Press
Chaisson, E (2000) Cosmic Evolution: The Rise of Complexity in Nature Cambridge, MA: University of Harvard Press
Darwin, C (1859) On the Origin of Species By Means of Natural Selection or the Preservation of Favoured Races in the Struggle for Life. London, England: Murray London
Goodsell, D.S (2009) The Machinery of Life: New York, NY: Springer Verlag
Mayer, E (2001) What Evolution Is New York, NY: Basic Books
Sagan, D Schneider. E (2005) Into the Cool: Energy Flow, Thermodynamics, and Life Chicago, IL: The University of Chicago Press