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The term energy is used in a variety of meanings. We speak of an energetic person, we say we are devoting a lot of time and energy for a task, we refuse to walk farther because we have no more energy left. We know that we need it for our comforts and civilization, indeed even for our survival. The Industrial Revolution has energy at its base. Much of applied science is related to the use of energy to serve human needs and wants. The phenomenal world is a complex process of energy transformations, and so is life, and so is the technological world.

The concept of energy is implicit in many ancient writings. The Vedas of India, which date back more than 3,000 years, speak of the divine as cosmic energy. Ancient Greek thinkers used the term energeia to mean activity. Medieval thinkers felt that there was some aspect of motion that remains unaltered when changes occurred. Soon after the rise of modern science in the 17th century, scientific thinkers tried to quantify this invariant feature of motions. By the beginning of the 19th century, Thomas Young redefined the quantitative meaning of energy.

Associated with energy are the ideas of work, force, power, and action. In physics, work and energy are related. Here, work is not just something that we do; it is not a job for a paycheck, nor a task to be submitted to someone, but that which leads to energy. Work, for the physicist, involves a force that moves bodies. There is no work in unchanging motion. There is no work when the effects of forces cancel out. But when forces act and displacement occurs, then we say that work has been done.

Like force and speed, work and energy are physical quantities. There are several (equivalent) units for the measure of energy. The energy unit in the international scientific system is called the joule, abbreviated as J. Another commonly used unit of energy, especially of heat energy, is the calorie (cal).

We need energy for our survival as biological beings: our hearts and lungs, blood and brains are constantly doing work. We move around, too. And as technological creatures, we also use (if not need) energy for heating, cooling, and lighting our homes, for transportation in vehicles, for entertainment (TV, radio), for cooking and refrigeration, for communication (telephone, fax). All this can add up to quite a bit.

There are all these movements: gentle breeze, smooth streams, wild waves, and much more. Every motion is a manifestation of energy. Energy appears in many forms, and one of its most common forms is motion.

Ordinarily, we look upon motion only in terms of changes in location. But when an ant creeps, a runner runs, an eagle flies, when the pendulum swings, the wheel turns, the rocket zooms, and when the planet moves, they all display a burst of energy. We call this their kinetic energy. When Descartes spoke of matter in motion, he was recognizing the universality of kinetic energy. From microcosmic minuteness to the grand galaxies, every bit of matter, a speck or stupendous, is endowed with kinetic energy.

Heat, light, and electricity can all be reduced to some kind of motion or another. This kinetic view of nature: a natural outgrowth of the Cartesian sweep of matter in motion.

We give a kick to the soccer ball, it flies and rolls and comes to a stop. We give a push to the child’s swing, its oscillations gradually weaken and bring the swing to a halt. We spin the wheel on its axle, and it slacks in speed and loses its rotational motion. Even the furious meteorite that comes zooming into our atmosphere slows down, losing speed. Every moving thing here on earth slows down and stops, sooner or later. Put differently, all kinetic energy disappears.

All the kinetic energy in these cases was dissipated by friction. In the case of the meteor, it is glowingly obvious for the intruding stone burns bright and is spectacular as a falling star. The ball and the swing lose their energy to friction, too, but the heat generated is slight and barely perceptible.

Up there beyond the heavens where no air pervades, the kinetic energy of moving bodies does not get dissipated. So the moon revolves and planets orbit, never losing their kinetic energy. If they did, much havoc would follow. It is good space is really empty.

Like the soul of religions, energy is never recognized in its unclad glory; it manifests itself in different garbs. There is heat and light and motion, sound and electricity, too. All these are energy of one kind or another. From all these work can be done.

Energy manifests itself in two essentially different forms: First there is motion, which may be ordered or random; then there are waves, material or immaterial. What is significant for us humans is that these manifestations affect us in ways that not only serve our basic needs for survival, but also add richness to our lives. Thus, for example, ordered motion or mechanical energy serves us in locomotion, whereas random molecular motion affects us as heat and warmth. Material waves include the ups and downs of water waves, vibrations of strings and air columns, which in turn produce sound and music, and a whole range of immaterial waves, which strike us as light and radiant heat.

The world of perceived reality is thus made up of energies in various forms. These different forms of energy create different impressions. We go through the pains and pleasures of life without pausing to consider the energy aspects of the world. But they are there at every turn, sometimes blatantly obvious, sometimes not so apparent, and in other contexts stealthily hidden, as it were, waiting to be released when opportunities arise.

Heat can be converted to motion (kinetic energy), motion into electricity, electricity into light, light into sound, and so on. Indeed, such transformations are the root of perceived reality. The phenomenal world is an endless complex of energy transformations.

The transformations are endless, and they are complex, too. Even the most trivial episode in the arena of cosmic history involves complicated energetic changes. Just consider snapping a finger, which calls for muscular effort. The energy generated for that was from a series of biochemical reactions involving molecules (proteins, fats, etc.) whose source is ultimately the green kingdom, which captured energy from sun light, which in turn energy came from the core of the sun as a result of nuclear reactions that occurred, as per our calculations, some 10,000 years ago.

This is a most fascinating story: this conversion of energy from the sun’s core several thousands of years ago to its climax in the snapping of my fingers. And then it goes on, for that mechanical energy became sound and got dissipated in the air, giving a slight boost to some molecules. What a mind-boggling chain of transformations! This is an insignificant instance of countless transformations occurring at all scales of perceived reality.

At every pause we take to reflect on the roots of perceived reality, we never cease to wonder at the magnificence of it all, in scale and in variety, in complexity and in simplicity. How fortunate that we can fathom some of this, and wonder at it all!

Like exchange rates in currency, so much heat is equivalent to that much mechanical energy; that much mechanical energy is equivalent to so much light, and so on.

Energy is the insubstantial dynamic dimension of the physical world: manifest as light and sound, as heat and motion, or is simply held trapped in positional constraints and in molecular configurations, ready to be released when provoked. Matter, on the other hand, is the static substantial feature of the world, concentrated and massive, localized in space, exerting nevertheless long range forces on other pieces of matter in the universe.

We have a world of matter and energy, of substance and action, one making us feel we are in a tangible world, the other giving us the sensation of heat, the joys of sound, and the effulgence of light. Matter undergoes umpteen transformations, while retaining its total mass; and energy does a very similar thing, too, maintaining its quantitative integrity also.

It turns out that these two dimensions of perceived reality, one so different from the other, are in fact two aspects of one and the same entity, for which we have no simple name. We may regard matter as an extremely concentrated form of energy, and energy as a very diffuse and insubstantial manifestation of matter.

Energy, the life-breath of the universe, will never by annulled. There will always be a residual heartbeat even if the universe were to reach asymptotic chillness. Inactivity may be for the lazy, rest for the tired, and inertness for the lifeless. But a modicum of energy will always be associated with the atoms and the ultimate oscillators of the universe. Here is a root of perceived reality that has been unearthed by scientific inquiry: We live in a world that has been keyed to innate dynamism.

Physics has also revealed that energy simply does not vanish even where there is absolute nothingness. Like writings on a blank blackboard, virtual (ephemeral) particles appear and are promptly erased, as if strewn and sucked back by some cosmic pump. This is possible because at the underlying levels there are inherent latitudes as to the strictness with which matter and energy are conserved.

The kind of dynamic vacuum mentioned above is no irrelevant quirky behavior in some remote corner of the universe. It is not a stray event like a comet or a supernova, which are interesting but not regular features of the observed world. Rather, if current cosmological models have any truth, virtual particles in the nether world are the ultimate culprits that are responsible for the emergence of the universe. They are what gave rise to this material universe of ours, and in quite unexpected ways, too.