We have the famous equation $E = mc^2$, and we also believe that matter is made of particles.

Then, What is the energy made of? If the two are interchangeable, there must be some common building block to both for sure. Isn't it?

If energy is made of "Nothing", how could it be converted to matter?

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You may find this useful: leifiphysik.de/web_ph08_g8/lesestoff/01feynman/feynman_engl.htm – mtrencseni Sep 7 '11 at 22:03
quite intriguing.....well what i can only say is that as matter and energy are interchangeable, one might be made of the other. Probably some string theoretician might help! – Vineet Menon Sep 8 '11 at 5:14
Energons, obviously (-; – mbq Sep 8 '11 at 7:21
It's turtles all the way down. – Colin K Jan 27 '12 at 17:30
The question you should worry about is "What is not made of energy?" – Tobias Kienzler Dec 7 '12 at 15:34

Energy is not made of anything, energy is a term used to describe a trait of matter and non-matter fields. When matter has velocity, for example, it is said to have kinetic energy. There are also various forms of potential energy. These forms of energy can increase or decease each other, but when all the forms are added together, the value remains constant.

Consider the case of thermal energy. For a very long time people thought that heat was the manifestation of a substance called phlogiston (see this article). It was thought that the flow of this substance into and out of things was the medium of temperature changes. Eventually, people came to understand that heat is an emergent property of the collective movement of the particles of materials. Thus, the concept of heat energy went from that of a substance to a description of the trait (particularly motion) of matter.

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How can matter be converted to trait of matter? Can a person be converted to age? It just does not make sense. Energy must be made of something. Or else mass itself is not made of anything. – Jus12 Sep 8 '11 at 4:08
When people say "matter is converted to energy" it normally means the matter is being converted to some non-matter form. It also normally means the person in question is not a physicist ;-) Physicists rarely (never?) use such misleading terminology; instead we talk about e.g. pair annihilation. – David Zaslavsky Sep 8 '11 at 6:07
@david: then what about mass defect in nuclear reactions? Even in that case as u say matter is converted to energy! – Vineet Menon Sep 8 '11 at 7:35
@Vineet: have a look at this question to address that point. – David Zaslavsky Sep 8 '11 at 7:47
@jus: matter can be converted to a trait of matter through events like nuclear fission. When an atom fissions, the sum of the masses of the fission products is less than the mass of the original atom. The system retains the same energy because the fission products have the kinetic energy of their motion. – AdamRedwine Sep 8 '11 at 10:37
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Energy only exists because of some difference. For example kinetic energy - it only exists relative between two objects, since movement can only be defined relative to another object. Heat likewise - which is movement on molecular scale, but here we can measuere the movement of molecules relative to other. "Potential" energy as mgh, of heigh above ground, is also only relative to other objects. So indeed, it is a state of the object, that can be related to movement or acceleration (remember an object accelerates in gravity). Electric and chemical energy is likewise due to objects moving relative to others, or being held against a force. Ultimatly, work done, or energy, is movement with a force over a distance, while potential energy exists because an object is held against a force that would have caused it to move.

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I think you have the definition of "energy" is not it really is. Energy is not a real physical state nor an "intangible substance" but only a scalar that is assigned to the state of the physical system, ie, energy is a tool or mathematical abstraction of a property of physical systems.

For example, one can say that a system with zero kinetic energy at rest.

Used as an abstraction of physical systems by the ease of working with scalars, compared with vector quantities such as speed or position. For example, in mechanics, can fully describe the dynamics of a system based on the kinetic, potential, comprising the mechanical energy in Newtonian mechanics has retained ownership, that is invariant in time.

Energy is a physical quantity that occurs in various forms, is involved in all processes of change in physical state is transformed and transmitted depends on the fixed reference system and is retained.

So every body can have energy, thanks to his motion, chemical composition, its location, its temperature, its mass and some other properties. The energy is defined as the ability to perform work. Energy and work are equivalent and therefore are in the same units.

Heat is a form of energy, so there is an equivalence between energy units and heat. The ability to work in a given amount of time is power.

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I will have a go at this since it came up once more.

To start with when we use relativistic equations we are in the realm of particle/nuclear physics, one way or another.

In the formula that puzzles you, $E = mc^2$, the mass is a variable too. So it is an equation that gives an equivalence of one variable to another. So as others have observed, this formula is a mathematical convenience, it follows the conservation laws that are imposed by the differential equations that describe all systems in the microcosm, and should absolutely hold.

Secondly the mass itself in your formula is the relativistic mass and can be defined for all particles and particle systems whether moving or at rest:

$m_r=E/c^2$ or equivalently $m_r=\gamma\times m_0$

where $m_0$ is called the rest mass of a particle or a system and is an invariant quantity under four dimensional transformations, characterizing the Energy_momentum four vector of the system. $m_0^2=E^2-p^2$ where $E$ is the total energy of a system of particles and $p$ the total momentum.

When it is one particle under observation it is the mass that you will find in the table of masses for particles, and can be considered the building block of matter as we know it except for particles at the limit of $m_0=0$. The photon, for example ,has energy $E=h\nu$, but $m_0=0$

When a single particle is moving its relativistic mass rises according to the formula above, thus $m_r$ itself counted in units of $m_0$ is a continuous variable derived from the variables of the system under observation.

Now if we go to the bottom of what we know of the microcosm, we know that it consists by the particles given in the Standard Model table playing ball with each other according to very specific rules, called Feynman diagrams. They interact with each other throwing gauge bosons and turning into new particle manifestations with new $m_0$ masses conserving all necessary quantum numbers. There is never any energy floating by itself in the vacuum. It is always carried by a particle according to the formulas given above.

So the answer for the microcosm is, in a nutshell, that neither $m_r$ nor energy are composed of anything. Only $m_0$ exists and the rest are mathematical definitions useful for calculations. Since the macrocosm is made up by the particles in the microcosm this holds true for the macrocosm too, though relativistic concepts are irrelevant for the everyday velocities achievable .

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From one angle we say energy is a property of something eg kinetic and from another we say light is only energy. Shouldnt we make our mind up? What is the confusion here?

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As we know that everythihg is made of energy (by $e=mc^2$).everything has mass and recently discovered that a body has mass due to The Higgs Boson.if energy is not made of anything then it will not form an object because anything that is not made of anyhting can't form a object.And that object has mass than it has also Higgs Boson so from this we can say energy is made of Higgs Boson.

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