Even today, physicists are at a loss to fully define energy. At the same time, the features of this extraordinarily important “something” have been studied in detail and are well known. It goes without further saying that this “something” plays a decisive role in every aspect of human activity, especially in the technological, the economic and the political sectors. The energy crisis and nuclear weapons have made this abundantly clear to everyone.

The first, astounding feature of energy: it is indestructible. It can neither be created nor destroyed. The notion that any particular organ of any organism can “create” energy is therefore an illusion. Whatever energy an organism requires must either be given to it by its parents, or that organism must extract it from the environment on its own.

The second, no less astounding feature of energy: it takes on a variety of different forms (Fig. 1) and can be converted from each one of these forms into any other form. How this works in practice can best be demonstrated using an example:

One of the numerous forms of energy is gravitational energy. Masses exert an attraction on each other. This explains why the earth orbits around the sun and is forced by the latter into a particular trajectory. It also explains why our planet exerts a powerful pull on all the objects on its surface, whether these be human beings or stones. When rivers flow “downstream”, then they are in fact moving closer to the center of the earth. And this provides us with a first example of energy conversion. The energy associated with the river’s motion (kinetic energy), causing it to excavate its channel bed and sweep away sediment and tree trunks, is converted gravitational energy. The steeper the slope, the higher the energy. If we install a turbine under a waterfall in order to power a generator, then we can successfully convert the water’s kinetic energy into another form of energy, namely electricity. If we send this along wires to a factory housing an electric oven, then we convert electricity into heat. This is the term we apply to the vibration of the smallest particles of matter – atoms and molecules; this heat spreads both through the air and via surrounding objects and fluids – it “heats” something up. If we send the electric current to a light bulb, then we convert electric energy into light energy. If we operate a generator with this electric energy, then we convert electricity into kinetic energy. And if we let the motor power a pump that conveys water up into a higher-lying basin, then we have again converted the kinetic energy into gravitational energy, which remains stored in the reservoir: in this case we refer to potential energy, which can immediately be released as “free” energy that can do work when we open the valve and the water jet shoots “downhill”.

Other forms of energy that have not been mentioned above include magnetism, surface tension, chemical energy – that force which combines atoms into molecules – and the especially powerful nuclear energy, which binds the tiny components of the atomic nucleus (the nucleons) to one another.

Energy forms:

1. kinetic energy (energy of movement, e.g. of a cannonball)

     heat (vibrations of atoms and molecules)

2. gravitational energy (attraction of masses, e.g. between the sun and the earth)

3. electromagnetic energy:

     light
     electricity
     chemical energy (the bonds between atoms, giving rise to molecules)
     surface tension (which determines the size of water drops)
     magnetism etc.

4. nuclear energy (holds the subatomic particles that form atomic nuclei together)

5. electron rest mass energy (forms the mass of the subatomic particles)

Fig. 1: Overview of the key manifestations of energy. Each of these manifestations can be converted into any other form. Historically, however, most have been quantified using different units such as erg, calories, horsepower, meter-kilogram force, watt-seconds etc. Today, the common measure for all manifestations is the joule.
 

In the present context, we need only note that all these forms of energy, which appear to be quite different from one another, are ultimately one and the same thing – that invisible “something” that harbors highly versatile capabilities⁴.

At the organismic level, to which we now turn in more detail, energy has a special significance because none of the organism’s manifold functions would be possible without it. As everyone knows, plants and animals are composed of cells in which exceptionally complex processes occur. Each of these processes requires energy. Cells are combined into organs, which perform specialized tasks in the body, a system which is based upon a division of labor. In plants, the leaves fulfill an entirely different function than roots or flowers. In animals, the sensory organs, locomotory apparatus, nervous system and digestive tract are structured entirely differently. Energy is used to perform highly differentiated tasks based on widely differing material structures. In reproduction, energy is first required to develop these reproductive organs, then to regulate, control and maintain them. Energy can be made to perform exceptionally diverse tasks depending on how the respective matter is structured⁵.

As energy cannot be created, every organism must extract what it needs from the environment and then apply it accordingly. This is a primary function because every other task already requires energy, i.e. they require that surplus energy be available. From this perspective, energy – as that invisible “something” – becomes decisive. Once an organism loses the ability to gain and apply the energy reserves it needs for its functions, then its life ends and it “dies”. The organs become useless and decompose.

Note that organisms must do more than merely acquire the precise amount of energy from the environment that they need to cover their overall activity. Another peculiarity of energy enters the calculation here, namely the process of conversion: virtually no one form of energy is transferred 100% into another. As a rule, a considerable portion is converted into heat that is lost to the surroundings. Technicians refer to the “efficiency” of the energy conversion. Thus, for example, an automobile motor converts the fuel’s chemical energy into kinetic energy that propels the car forward. The efficiency here is 40%. This means that 60% of the work that the chemical energy in the fuel could theoretically do is lost in the process (escapes into the environment as heat) and only 40% is actually used to move the car. This loss is significantly greater when electric current is converted to light in a light bulb. The efficiency here is only 9%. Thus, only 9% of the applied energy is converted into the desired form, and the loss exceeds 90% (“entropy”).

Long series of energy conversions take place in the body of every organism before the various organs can use the raw energy gained to fulfill their specialized tasks. This means that organisms must consume many times more energy than their varied functions actually require. This often neglected fact underlines our first premise – that energy gain plays a crucial role in the living world. Any organism that fails in this key endeavor is doomed (Fig. 2).
 
 

Fig. 2: Energy gain in living organisms. No movement and no life functions are possible without useful energy. Each organism must therefore acquire and harness more energy from the environment than its overall activity requires. If the organism is unsuccessful in doing this, its life processes cease and it dies.
(Energiequelle...energy source, Energieaufwand der Erwerbstätigkeit...energy requirements for the acquisition process, Energieeinnahme...energy consumption, Lebewesen...organism)
 

Life is a process that depends on the interplay between many quite different activities. All require energy. Without energy there is no movement, no development, no capability. Not even for a millisecond.
 

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