We scientists talk about energy, and derive equations with energy mathematically expressed in the equation as though we understand energy. The fact is: we do not. It is an indirectly observed quantity. We infer its existence. For example, in physics, we define energy as the ability of a physical system to do work on another physical system. Physics is one context that uses and defines the word energy. However, the word energy has different meanings in different contexts. Even the average person throws the term energy around in phrases like, “I don’t have any energy today,” generally inferring a lack of vigor, force, potency, zeal, push, and the like. The word energy finds its way into both the scientific community and our everyday communications, but the true essence of energy remains an enigma.

The concept of energy is an old concept. It comes from the ancient Greek word, “enérgeia,” which translates “activity or operation.” As previously stated, we do not know the exact essence of energy, but we know a great deal about the effects of energy. To approach a better understanding, consider these four fundamental properties of energy:

1. Energy is transferable from one system to another.

Transferring mass between systems results in a transfer of energy between systems. Mass and energy have been inseparably equated, since 1905, via Einstein’s famous mass–energy equivalence equation, E = mc2, where E is energy, m is mass, and c is the speed of light in a vacuum. This equation is widely held as a scientific fact. Experimental results over the last century strongly validate it. Typically, mass transfers between systems occur at the atomic level as atoms capture subatomic particles or bond to form products of different masses.

Non-matter transfer of energy is possible. For example, a system can transfer energy to another by thermal radiation (heat). The system that absorbs the thermal radiation experiences an increase in energy, typically measured by its temperature. This is how the radiators in a house raise the room temperature. Here is another example: If an object in motion strikes another object, a transfer of kinetic energy results. Consider billiard balls. When one ball strikes another, it imparts kinetic energy to the ball it strikes, causing it to move.

2.  Energy may be stored in systems.

If you pick up a rock from the ground and hold it at shoulder height, you have stored energy between the rock and ground via the gravitation attraction created between the Earth and rock. You may consider this potential energy. When you open your hand, the rock will fall back to the ground. Why? The answer is straightforward. It required your energy to hold the rock in its new position at shoulder height. As soon as you, by opening your hand, released the energy that you were providing, it reduced to a lower energy state when the gravitational field pulled the rock back to the ground.

Any type of energy that is stored is “potential energy,” and all types of potential energy appear as system mass. For example, a compressed metal spring will be slightly more massive than before it was compressed. When you compress the spring, you do work on the system. The work on the system is energy, and that energy is stored in the compressed spring as potential energy. Because of this stored potential energy, the spring becomes more massive.

3. Energy is not only transferable–it is transformable from one form to another.

Our example regarding the rock falling back to the ground is an example of energy transformation. The potential energy was transformed to kinetic energy when you opened your hand and released the rock. This is what caused the rock to fall back to the ground. Here is an industrial example. Hydroelectric plants generate electricity by using water that flows over a falls due to gravity. In effect, they are transforming the falling water (gravitational energy) into another form of energy (electricity).

4. Energy is conserved.

This is arguably the most sacred law in physics. Simply stated: Energy cannot be created or destroyed in an isolated system. The word “isolated” implies the system does not allow other systems to interact with it. A thermos bottle is an example of an isolated system. It is preventing the ambient temperature from changing the temperature inside the thermos. For example, it keeps your coffee hot for a long time. Obviously, it is not a perfectly isolated system since eventually it will lose heat to the atmosphere, and your coffee will cool to the ambient temperature that surrounds the thermos bottle. For example, in your house, the coffee in a cup will cool to room temperature.

In summary, energy may be transferred, stored, and transformed, but it cannot be created or destroyed in an isolated system. This means the total energy of an isolated system does not change.

Next, we will consider energy in different contexts. Unfortunately, since we do not know the true essence of energy, we need to describe it via the effects we observe in the context that we observe them. Here are two contexts:

1)   Cosmology and Astronomy

Stars, nova, supernova, quasar, and gamma-ray bursts are the highest-output mass into energy transformations in the universe. For example, a star is typically a large and massive celestial body, primarily composed of hydrogen. Due to its size, gravity at the star’s core is immense. The immense gravity causes the hydrogen atoms to fuse together to form helium, which causes a nuclear reaction to occur. The nuclear reaction, in effect, transforms mass into energy. In the cosmos, mass-to-energy transformations are due to gravity, and follow Einstein famous equation, E = mc2 (discussed previously). The gravity can result in nuclear fusion, as described in the above example. It can cause a dying star to collapse and form a black hole.

2) Chemistry

Energy is an attribute of the atomic or molecular structure of a substance. For example, an atom or molecule has mass. From Einstein’s mass-energy equivalence equation, (E = mc2), we know the mass equates to energy. In chemistry, an energy transformation is a chemical reaction. The chemical reaction typically results in a structural change of the substance, accompanied by a change in energy. For example, when two hydrogen atoms bond with one oxygen atom, to form a water molecule, energy emits in the form of light.

Other scientific contexts give meaning to the word energy. Two examples are biology and geology. Numerous forms of energy are accepted by the scientific community. The various forms include thermal energy, chemical energy, electric energy, radiant energy, nuclear energy, magnetic energy, elastic energy, sound energy, mechanical energy, luminous energy, and mass. I will not go into each form and context for the sake of brevity. My intent is to illustrate that the word energy in science must be understood within a specific context and form.

As mentioned above, we truly do not know the essence of energy; we infer its existence by its effects. The effects we measure often involve utilizing fundamental concepts of science, such as mass, distance, radiation, temperature, time, and electric charge. Adding to ambiguity, energy is often confused with power. Although we often equate “power” and “energy” in our everyday conversation, scientifically they are not the same. Strictly speaking, in science, power is the rate at which energy is transferred, used, or transformed. For example, a 100-watt light bulb transforms more electricity into light than a 60-watt light bulb. In this example, the electricity is the energy source. Its rate of use in the light bulbs is power. It takes more power to run a 100-watt bulb than a 60-watt bulb. Your electric bill will verify this is true.

What is it about energy that makes it mysterious? Science does not understand the nature of energy. We have learned a great deal about energy in the last century. The word energy has found its way into numerous scientific contexts as well as into our everyday vernacular, but we do not know the fundamental essence of energy. We can infer it exists. Its existence and definition is context sensitive. We do not have any instrument to measure energy directly, independent of the context. Yet, in the last century, we have learned to harness energy in various forms. We use electrical energy to power numerous everyday items, such as computers and televisions. We have learned to unleash the energy of the atom in nuclear reactors to power, for example, cities and submarines. We have come a long way, but the fundamental essence of energy remains an enigma.

In the next post, we will discuss another aspect of energy that haunts the scientific community. Does all reality consist of discrete packets (quantums) of energy? Are mass, space, time, and energy composed of quantized energy? We can make a reasonably strong case that they are. It is counterintuitive because we do not experience reality that way. For example, when you pick up a rock, you do not directly experience the atoms that make up the rock. However, the rock is nothing more than the sum of all its atoms. If all reality is made of quantized energy, we live in a Quantum Universe. What exactly is a Quantum Universe? Stay tuned, and we will explore what a Quantum Universe is in the next post.

Source: Unraveling the Universe’s Mysteries (20120, Louis A. Del Monte