There are essentially four kinds of energy sources:
(a) Cyclic sources: Some of our energy sources, though they are being used up, are also being continually re-formed. The most important example of this is food energy. Although it is being consumed regularly and ceaselessly, food is also being formed at the same time by the various processes of agriculture, farming, the breeding of animals, etc. This is also the case with wood. As long as green plants (and the sun) are with us, this energy source will re-emerge regularly. Note that a gigantic natural factory is indispensable for this cycle to operate. It is practically impossible for humans to accomplish this all by themselves. Although we refer to this as a cyclic process it must be understood that it is not the energy that is being recycled, but rather the atoms and molecules that lock in the solar energy continuously pouring over the planet. These molecules (in the form of food) merely serve as buckets to capture and maintain that energy. Once the energy is used up, the bucket returns to the ground, practically demolished. They are then formed again and filled with energy by the green plants, and come back to serve living creatures.
(b) Finite sources: Fossil fuels are among our chief sources of energy today. It took nature several million years to form coal, oil, and gas. But during the past century we have been using them at a fairly rapid rate. Although we have used up barely 2% of these resources, with our increasing rate of consumption we will deplete the remaining 98% in less than a century. There is only a finite amount of fossils buried underground. These energy sources, on which present day technology largely depends, pose serious threats to our future for the simple reason that they will not be available for an indefinite period of time. Even if we do not waste fossil fuels, a time will surely come, sooner or later, when it will all be depleted. What will we do then? This is what prompts the search for other forms of energy.
These other forms come under two categories: Those sources of energy that are known to us, but which we have not yet been able to tap effectively; and those which are as yet unknown to us.
(c) As yet fully untapped sources: Nature is filled with huge reservoirs and transformations of energy. Humans have recognized and calculated these stupendous sources. But our plight is somewhat like that of the penniless pauper who is staring at the gloriously decorated display windows of a store: He knows it is all there, but how can he lay his hands on them? Consider, for example, the energy liberated in a lightning flash. It is equivalent to that obtained by burning 12 kg of coal, corresponding to the average energy consumption of a household during an entire month. There are about 100 lightning flashes occurring in the earth’s atmosphere every second of a 24 hour day, and all this energy goes wasted as far as we are concerned.
Similarly, there is a constant flow of heat energy from the interiors of the earth to the surface, and the total amount of this exceeds that of humanity’s daily energy requirements. But we have not yet developed realistic methods of harnessing this energy, except when parts of it occasionally gush out through hot springs. These are but two examples of such untapped sources. Likewise, the oceans lash out tremendous amounts of energy as waves and tides: about 17 billion joules of energy each second, it has been estimated. This is enormous compared to humanity’s current rate of use of electrical energy which is less than a billion joules a second. Then there is all the wasted power in the winds, though small amounts of this are being captured by windmills here and there. Finally, we have that (for all practical purposes) infinite reservoir of energy: our central star. We get incredible amounts of energy from the sun interminably, and if we could only tap solar energy more effectively all our energy problems (it would seem) would be solved once and for all.
(d) Speculative systems: Vast amounts of energy are given out in lightning flashes. Harnessing that energy is as yet at too speculative a stage. There are other such (as of now even theoretically) impractical ideas. One has talked of tapping the rotational energy of the earth, the energy of cosmic rays, the energy from the great flux of neutrinos that are cascading the earth in never ending torrents of great but imperceptible intensity. None of these is taken seriously at the present time.
But imagination and speculation have always played a role, not only in literature and in art, but in pure and applied science as well. As long as, in any given context, facts and realistic appraisals are carefully distinguished from interesting fantasies, there is no grave danger. It is no doubt difficult sometimes to draw the line between science fiction and real science. Indeed, occasionally the science fiction of one generation becomes the science of the next. And scientists themselves indulge in fantastic speculations, consciously or otherwise. Speculative systems are as interesting, if not as valuable, as great ideals.
September 14, 2010