The Energy of Life: - Guy Brown

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remained obscure throughout the nineteenth century. It was gradually established that respiration – oxygen consumption, carbon dioxide and heat production – occurred within the tissue cells, rather than in the lungs or blood. It was thus suggested that muscles might work as biological steam engines using the heat generated by respiration to drive contraction. But by the end of the century, it was realized that this would not work, as the Second Law of Thermodynamics indicates that heat is a very inefficient source of work unless the temperature difference between machine and environment is very high. At normal physiological temperatures a heat engine would therefore be extremely inefficient, generating very little work for the amount of food burnt. The only realistic way of using respiration to drive muscle contraction was to bypass heat production and pass the energy released by respiration through some intermediate energy store to muscle contraction, without releasing the energy as heat. But it took another century to work out how this feat was achieved.

      The historical trail we have followed in pursuit of the secrets of life and energy has branched many times as the questions have multiplied, and the answers have led us off into territory ever more obscure and abstruse. To summarize, before pressing on in the next chapters to the summit of present understanding of body energy: we started by looking at the general modes of biological explanation in early cultures where energy and life were not distinguished from each other and where all movement and change were attributed to anthropomorphic souls, gods or spirits. Energy, enthusiasm and life were given by the gods and equally spirit and health could be taken away by the gods or devils. Mechanisms were not considered, because ‘mechanism’ was not involved. In ancient Greece and Rome the role of gods and souls gradually diminished. Energy came in the form of pneuma, a spirit of the air, circulating in the body and providing the ‘go’ of life. In Renaissance and Enlightenment Europe, spurred on by advances in technology, gods and souls were ejected from science and replaced by cold mechanics. Crucially, hypotheses were now tested by experiment rather than rational plausibility and this was aided by the injection of mathematics into scientific theories and experiments. Pneuma and spirits were replaced by ‘forces’ and ‘laws’. A component of the air, oxygen, was found to be essential to life and consumed inside the living body in the process of burning digested food, resulting in the production of body heat. This process of respiration was eventually found to be located in the cells of the body and carried out by enzymes, the molecular machines of the cell. The various forces of nature were found convertible between each other and into movement and heat and, thus, were united in the common concept of energy, the universal source of all movement and change. The body then became an energy converter (or engine), channelling the energy released by burning food into movement and thought, but how exactly this was effected was unknown.

      The appealing idea of the history of science as a continuous ascent towards the pinnacle of modern truth, is, of course, anathema to most historians. They point out this view of history arises from taking the contemporary truth and weaving a narrative towards it – carefully selecting from the past. My brief historical overview gives little idea of how scientists really thought and operated in the past. It does, however, give us a sense of where our present-day concept of energy came from and how it evolved; and now we must follow it right up to the constantly moving present, where a number of shocks await.

       Chapter 3 ENERGY ITSELF

      WHAT IS ENERGY?

      I taught bioenergetics (the science of body energy) in Cambridge for many years before I realized that I did not, myself, understand what energy was. Tutorials are meant to be cosy but fiercely intellectual chats between a teacher and one or two students. However, teachers can often rattle on without knowing what they are talking about. One fine day I discovered that was true of me and energy. Part of the problem with energy is that it is an abstract idea, so that one answer to the question ‘What is energy?’ is ‘A concept existing in a scientist’s head’. But another, more subtle problem is how the concept of energy has evolved historically, so that many layers of meaning, not always consistent, have been superimposed on the words and symbols. So take heart, if at first you do not understand the meaning of energy, it will not necessarily disqualify you from either doing scientific research or teaching bioenergetics at Cambridge! In science, as in life, you do not necessarily have to understand a concept in order to be able to use it.

      According to current scientific ideas, energy is not an invisible force field coursing through the body, moving arms and legs and cooking up thoughts in the brain like some benign ghost dashing around pulling the levers of body and mind. The modern idea of energy is more like that of money. Money gives the capacity to buy things, coming in many forms, such as coins, notes, cheques, credit cards, bank accounts, bonds, gold etc. It can be used to buy many sorts of things, such as hats, houses and horses. Money allows the exchange of these things at a fixed rate, so that I can, for example, exchange a fixed quantity of coins for one horse. ‘Energy’ is a capacity for movement or change in a physical or biological system. It comes in many forms, such as chemical energy, electrical energy, or mechanical energy and can be used to ‘purchase’ many forms of change, such as movement, chemical change, or heating. Energy quantifies the exchange between these things at a fixed rate, so that, for example, a certain amount of heating requires the expenditure of a certain amount of chemical energy. One important difference between money and energy is, however, that money and monetary value are not exactly conserved. You may pay £100,000 for a house one year, selling it for £110,000 or £90,000 the next year without having altered or improved the house and this £10,000 does not suddenly appear or disappear from elsewhere in the economy. You can burn a £10 note and money simply disappears in smoke. Neither money nor monetary value is absolutely conserved: there is no Economic equivalent to the First Law in Thermodynamics. If there was, Economics would be easier but we might also be poorer. Energy is strictly conserved, as expressed by the First Law of Thermodynamics, which states that during any change of any sort the total amount of energy in the Universe stays the same. If you use one hundred units of energy to raise a rock one hundred feet in the air, on your return a year later lowering the rock to the ground one hundred units of energy will be released. It may not be released in wholly desirable ways – the energy may be released as heat, sound or work depending on how the rock is lowered, but when the energy released is added up the total will be one hundred units.

      Money or monetary value is an abstract concept since it can reside in very different objects, such as coins or a bank account. Energy is similarly abstract since it is contained in many different types of thing, while not actually being them; energy rather is their capacity to produce movement or change. Energy is not in addition to the things themselves: it is rather as if an accountant were examining the situation, assessing the capacity for movement or change. For example if a rock is balanced at the edge of a chasm, it is possible to work out that if it were tipped into the chasm so much energy would be released as movement, noise, heat etc. Before the rock is moved, this energy does not reside in the rock or chasm any more than monetary value resides in coins or horses: this is because energy or monetary value are not tenuous forms of matter, but rather ways of quantifying the potential for change. Energy quantifies the capacity for movement or physical change within any particular situation.

      Energy is like money in another way. Money does not determine how or when it is to be spent; that is determined by the people spending it. Similarly, a rock balanced over a chasm may have a lot of energy but this does not determine if or when the rock may fall. Rather it determines whether the rock can fall or not. The presence of a million dollars does not determine how or when it will be spent but does mean that x number of houses, y amount of strawberries or z number of horses could be bought. Similarly the presence of one million units of energy does not determine how or when the energy will be used, but it does mean that x amount of heat, y amount of movement or z amount of electricity could be produced.

      The great American physicist Richard Feynman warned us of the abstract nature of energy in his famous Lectures on Physics:

      ‘It is important to realize that in physics today, we have no knowledge of what energy is. We do not have a picture that energy comes in little blobs of a definite amount.

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