– By Robert U. Ayres
From early childhood I have been fascinated by learning “how things work”. I suppose that is quite natural for children, but for one reason or another, most children are discouraged at an early age. The world is too complicated, there are too many “things” to learn about, there are conflicting short-term needs for time, they are told that parents or teachers or priests will explain it all in due course when we are “ready”, etc.
For some reason, however, I found a book called “The Strange Story of the Quantum” that introduced a curious idea, namely that there is an underlying simplicity that can be grasped by human intelligence, and that understanding “things” can sometimes be approached from “below”, so to speak rather than from the usual perspective “above”. I read that a fizzy-haired man named Albert Einstein had already found a way to put that underling simplicity in a single mathematical equation, a “theory of everything”. It is why I was attracted to physics.
Later I found out that Einstein’s equation didn’t actually explain everything. But that only left some room for me and others to fill in the gap. Needless to say, the gap remains unfilled. But now, late in my life, I think I have grasped – if not understood — some of the underlying simplicities. One of them is that “opposites attract”.
The attraction of Opposites: From quarks to Atoms
Early in the Big Bang (with in the tiny fraction of a fraction of a second, when the temperature was unimaginably high, pairs of elementary particles (quarks) and their anti-particles were created instantly destroyed by recombination, because anti-matter and matter attract each other. For some reason only one of these opposites exists in our part of the universe. Why? Nobody knows for sure. One suggestion is that back when the universe was expanding faster than the speed of light, there was a spontaneous “creation” event and the quark and its anti-quark flew apart in different directions. One carried mass and (possibly) charge and the other carried anti-mass and the opposite charge.
Nucleons (protons and neutrons) are constructed from quarks with positive mass and positive or neutral electric charges. Positive and negative charges attract each other. If particles annihilate each other they produce a high-energy photon, like a gamma-ray. But oppositely charged particles in close proximity (but kept apart by centrifugal force or some other force) can also create something new.
For example, electrons and protons, with opposite charges but with very different masses can combine to form a stable and long-lived couple. It consists of one charged particle (an electron) rotating – actually in a kind of three-dimensional cloud) around a proton. (By the way, the proton cannot actually combine with an electron to form a neutron, though a neutron can “decay” into a proton and an electron plus an anti-neutrino, which is another kind of particle.) That is how hydrogen atoms were created. (Why aren’t there any particles as heavy as protons, but with negative charges that form atoms with positrons? The answer is that they would be anti-protons and anti-hydrogen, which does not exist in this part of the universe.)
This attraction between opposites can be expressed as an underlying desire for “equilibrium” – a state where nothing changes. Attraction between charged particles can also be expressed as a “force law”. When particles with opposite charges – say electrons and positrons — actually collide, they annihilate each other. The outcome is a very energetic shower of photons or electro-magnetic waves. Are there stable relations (“marriages”) between opposite magnetic poles? Or between matter and anti-matter? I don’t know.
More interesting is the fact that atoms come in different kinds (sizes), depending on the number of protons in the nucleus. They can combine into molecules, also because of the underlying attraction between positive and negative electric charges. (The full explanation of how complex molecules are created depends on another attribute called “spin” – which has nothing to do with rotation, and also comes in two opposite types. I will not try to explain how spin comes into the story in one paragraph.)
There are practical ways of accumulating – and storing — electric charge (e.g. in a capacitor), thus creating a voltage. It is the attraction between positive and negative electric charges that creates a voltage difference that makes an electric current flow. A moving electric charge, or a current flow, in turn, creates a magnetic field, while a current flowing through a conductor in a stationary magnetic field causes a force on the conductor. That is how an electric motor works. Meanwhile an electrical conductor moving through a stationary magnetic field causes an electric current to flow. That is how a generator works.
North magnetic poles and south magnetic poles, e.g. on a stationary magnet, also attract each other. Magnetic poles are always found together in pairs, usually quite close to each other. Physicists have speculated about the existence of isolated magnetic poles, but so far none has been observed. If they did exist, other interesting combinations might exist also, but that is pure speculation.
The periodic table and chemistry
Electric charges also account for most chemical reactions. This happens because the electrons circulating around a nucleus of protons and neutrons, are organized into “shells”. The fact that electrons in an atom exist in distinct “shells’ is a consequence of a quantum mechanical rule, called the “Pauli exclusion principle”. This principle says no two objects can occupy the same physical location or “state”. (A “state” is defined as one solution of the so-called Schrodinger equation, which is more than most readers need to know, or will care to know.) Take my word that the shell structure has been confirmed in many ways.
The periodic table was introduced by Dmitri Mendeleev in 1869. It was originally a tool for predicting the properties of newly discovered elements, and is now an essential framework for this discussion. The order, from top to bottom and from left to right, is by atomic number, which also corresponds roughly to weight. Along a row (“period”) metals are on the left and non-metals on the right. Neighbors along a row tend to have chemical similarities based on electron configuration. Columns (“groups”) also reflect chemical similarities.
The elements on the first row (period) are hydrogen (H-1) and helium (He-2). The second period starts with lithium (Li-3) and ends with neon (Ne-10). The third period starts with sodium (Na-11) and ends with argon (A-18). The fourth period is longer; it starts with potassium (K-19) and ends with krypton (Kr-36). The fifth row period with rubidium (Rb-37) and ends with xenon (X-54). Finally, the sixth row starts with caesium (Cs-55 and ends with radon (Rn-86). The “rare earths” are in this period. The last period is for radioactive elements and trans-uranics, that can be ignored for now.
The column (group) starting below hydrogen consists of reactive alkali metals (Li, Na, K, Rb..) while the group starting one place to the left of helium on the right side consists of highly reactive halogens (fluorine, chlorine, bromine, iodine..). The group under helium consists entirely of inert, unreactive (“noble”) gases, characterized by complete outer shells. Chemistry students will be aware that the chemical combinations between alkali metals and halogens take place very easily, releasing energy as heat.
This is because the metals have a single loosely bound electron attracted only to the positively charged nucleus, while the halogens have a gap in their outer shells that they “want” to fill. When sodium meets chlorine, its loosely bound (extra) electron meets and fills a gap in the outer shell of chlorine, resulting in a tightly bound molecule, sodium chloride (NaCl), known as common salt. This is why alkali metals and halogens attract each other so strongly. It is still a case of opposites attracting.
The essential point here is that the elements in the periodic table tend to be related to each other chemically, according to the distribution of electrons in their outer shells. As stated above, near neighbors in the same row (period) of the periodic table also tend to have similar physical properties, such as melting points. For instance, going along the fourth row (period) from left to right we see most of the major ferrous metals chromium (Cr), manganese (Mn), iron (Fe), cobalt (Co), and nickel (Ni). These elements, in adjacent groups, all alloy readily with iron, which is lucky, because iron is by far the most common heavy metal on the Earth’s surface.
On macro-molecules and thermodynamics.
Molecules with different atomic compositions (and different shapes) are also “containers” of chemical energy. They can come together to create other molecules. There are two fundamentally different types of chemical reactions. One is called exothermic (like “combustion”) because it releases chemical energy as heat. This is a generalization of what happens when a hydrocarbon molecule containing chemical energy spontaneously re-combines with an oxygen molecule, forming carbon dioxide and water vapor and releasing that surplus chemical energy as heat.
The other process is called endothermic. It utilizes heat (from other sources) to form molecules with more “contained” chemical energy that would not be formed by spontaneous combinations (reactions) of smaller molecules. Ammonia is one example. Indeed all organic macro-molecules, from carbohydrates and fats to proteins are of this type. They all result from processes that utilize chemical energy from other sources (“food”) and store it in molecular form.
Some large macro-molecules have an interesting capability, called auto-catalysis. This means that, given a “food supply” of appropriate smaller energy-carrying molecules, they can reproduce themselves, leaving still smaller molecules, like carbon dioxide and water as “waste”.
Living organisms all depend on autocatalytic macro-molecules organized in such a way as to acquire and “digest” a “food supply” in the form of other energy-containing molecules. The first living organisms on Earth probably utilized chemical energy from sub-surface chemical processes in the magma under the Earth’s crust. Energy-rich sulfur compounds like hydrogen sulfide were (and still are) emitted from under-sea vents. Specialized ecosystems gradually evolved around such vents. The energy production system within the organisms was fermentation, a process by which glucose is converted to ethanol, releasing carbon dioxide and heat. It is the same process by which yeast makes bread.
The great evolutionary “invention” that enabled life to grow without depending on a finite food supply from under-sea vents, was photosynthesis. Luckily some primitive organism incorporated a new autocatalytic macro-molecule that had the capability of absorbing an energetic photon and using it to catalyze a reaction combining a carbon dioxide molecule and a couple of water vapor molecule to create a sugar molecule (glucose), releasing the excess oxygen molecules into the water. The sugar molecules were subsequently incorporated in new macro-molecules, thus reproducing the living organism.
At first the free oxygen in the ocean was quickly combined with dissolved methane, ammonia or free hydrogen. But most of it combined with dissolved metal ions, especially ferrous (incompletely oxidized) iron, to form insoluble (ferric) iron. (It is now called iron ore). But after hundreds of millions of years the dissolved iron was used up and free oxygen started accumulating in the atmosphere and the oceans. At that point, free oxygen in the water became a hazard to life itself.
The next important evolutionary “invention” (a billion years later) was an organism capable of oxidizing the glucose molecules inside itself by an alternative to the primitive fermentation process. The new process is called respiration. It is sixteen times more efficient than fermentation. This enables the organism to utilize free energy for other metabolic purposes, especially movement. The first organisms able to move (i.e. swim) in search of food needed much more chemical energy than stationary organisms that depended on diffusion or other natural processes to bring food. So respiration was important for two reasons. First it enabled mobility. And second, it provided a “sink” for the excess oxygen, which is highly reactive and toxic to simple organisms. Without organisms to consume the free oxygen, life would have destroyed itself soon after it started.
The invention or respiration enabled the creation of a whole new type of organism. The evolutionary descendants of the early photosynthesizers are called plants, whereas the descendants of the mobile respirators are now called animals. The plant kingdom – as we call it now– and the animal kingdom are another example of attractive opposites. Plants cannot exist without animals to consume the oxygen by respiration and animals cannot exist without photosynthetic plants to produce glucose.
As mentioned above, cellular reproduction at first depended on autocatalytic macro-molecules in a “soup” of suitable micro-molecules constituting both “food” (energy supply) and construction materials. The cloning of one macro-molecule in those circumstances was very slow, as it depended on diffusion and random encounters at the molecular level. The evolutionary “invention” of membranes to enclose the cell, allowing “food” molecules in, while allowing waste molecules (such as carbon dioxide) to escape, must have occurred at some point. The first bacterial cells, without a nucleus, were called prokaryotes.
Gradually, over hundreds of millions of years, some organisms became specialized in utilizing particular “foods”, based on location. Later, biological mergers occurred, as some organisms learned to live inside others, as “nuclei”, each performing a specialized service for the other. The autocatalytic molecules responsible for actual reproduction are called DNA, which is always located in the cell nucleus. Organisms with nuclei (eukaryotes) were more efficient than primitive bacteria and other organisms without nuclei (prokaryotes). The structure of an eukaryotic cell is illustrated below.
The last big evolutionary step – I am skipping a lot – was sexual reproduction involving females carrying eggs and males producing sperm. The two must combine physically in order to reproduce. True there are some species more complex than prokaryotes (cells without nuclei, e.g. viruses) that reproduce themselves without asexually. However, among multi-cellular organisms such species are rare oddities, suggesting that sexual reproduction has evolutionary advantages. I’m not sure what they are.
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About the author:
Robert U. Ayres is a physicist and economist, currently Novartis professor emeritus of economics, political science and technology management at INSEAD.. He is also Institute Scholar at the International Institute for Applied Systems Analysis (IIASA) in Austria, and a King’s Professor in Sweden. He has previously taught at Carnegie-Mellon University, and as a visiting Professor at Chalmers Institute of Technology. He is noted for his work on technological forecasting, life cycle assessment, mass-balance accounting, energy efficiency and the role of thermodynamics in economic growth. He originated the concept of “industrial metabolism”, known today as “industrial ecology” with its own journal. He has conducted pioneering studies of materials/energy flows in the global economy. Ayres is author or co-author of 21 books and more than 200 journal articles and book chapters. The most recent books are Energy, Complexity and Wealth Maximization (Springer, 2016), The Bubble Economy (MIT Press, 2014) “Crossing the Energy Divide” with Edward Ayres (Wharton Press, 2010) and The Economic Growth Engine with Benjamin Warr (Edward Elgar, 2009).
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