Nothing Is Made of Energy

Rub your feet on a carpet and you move electrons. Touch a doorknob and they come back, all at once, through a channel of air you have just torn apart. The answer to is it electrons is yes.

The other question — whether everything, matter included, is really just states of energy — does not survive contact with the first. Energy is not a substance. Nothing is made of it — matter included — and there is no ladder of energy levels along which one kind of thing turns into another kind of thing. Energy is a number you can compute about a system, and its entire importance is that the number does not change.

The instinct underneath the question is right, though, and it is one of the deepest things physics has found: there is a common substrate, and the different things in the world are different arrangements of it. The substrate just is not energy. It is fields.

Where this came from

Two questions, asked together, which turn out to pull against each other.

The first is mechanical. Lightning and a static shock are both electricity, so what is actually moving in them — is it photons, or is it electrons?

The second is the one sitting underneath: whether everything in the universe, matter included, is states of energy, with different levels of energy giving you different things.

The first has a clean answer, and working it out in full supplies everything needed to see why the second contains a category error. Not an idiosyncratic one, either — it is the same error carried by nearly every popular account of physics ever written, including the ones that deliver it as the punchline.

What a spark actually is

Worth doing in full, because every piece of the second question is already sitting inside the first.

Electrons get moved somewhere they would rather not be

Atoms are nuclei with electrons bound around them. How tightly a material holds its outermost electrons varies — rubber grips them hard, human skin holds them loosely. Press two such materials together and rub, and at every point of contact some electrons hop from the loose-gripping material to the tight-gripping one and stay there.

Now one object has more electrons than protons and the other has fewer. Neither is happy about it. Opposite charges attract, and you have just pulled a great many of them apart and left them apart. Doing that took work — your legs did it, against that attraction — and the work you did is still sitting there, unspent, in the arrangement.

That is what “charged” means. Not that something has been filled with a fluid, but that a population of electrons has been displaced from where the attraction wants them, and has not yet been allowed to return.

The field builds until the air gives way

A charged object surrounds itself with an electric field: at every point in the space around it, a specification of the force a charge placed there would feel. Bring your hand near a doorknob and the field in the gap between them gets stronger, because the same charge imbalance now spans a shorter distance.

Air is an insulator. Its electrons are bound to their molecules and cannot wander, which is why the charge sits on you rather than draining quietly away. But “insulator” is a statement about ordinary conditions, not a permanent property. Push the field past roughly three million volts per meter and the field itself pulls electrons off air molecules — it is simply stronger than the grip the nuclei have.

The moment a few free electrons exist, the situation runs away. Each one accelerates in the field, hits a molecule, and knocks more electrons loose; those accelerate and do the same. An avalanche, doubling and doubling, and in well under a microsecond a thread of air along the shortest path has been converted into plasma — a gas of separated electrons and ions, which unlike ordinary air conducts extremely well.

That thread is a wire that did not exist a moment ago. The accumulated charge pours through it and the imbalance is gone.

The flash and the crack are cleanup

Two things happen as the current dies. Free electrons recombine with ions, dropping into bound states around the nuclei, and each drop releases the difference in energy as a photon — that is the visible flash. Meanwhile the channel has been heated violently by the current tearing through it, and hot gas expands; the expansion is fast enough to be a shockwave, which reaches you as the snap.

So the light is not the electricity. The light is the sound of the door closing behind it.

Lightning is the same event, made enormous

Every step scales up without changing character. In a storm cloud, an updraft drives small ice crystals up past larger, heavier soft hail falling down. They collide, charge transfers on contact, and the two populations separate by weight — light positive crystals carried to the top, heavy negative hail settling lower down. Which way the charge goes depends on temperature, so a real storm ends up more layered than that — but the main split is the one that drives the stroke. It is the carpet-and-feet mechanism run by weather, at cubic-kilometer scale.

The field between cloud base and ground builds until air breaks down, a conducting channel is negotiated downward in steps, and when it meets an upward reach from the ground the accumulated charge dumps through in a return stroke. The channel reaches something like 30,000 K — several times the temperature of the surface of the sun — and that is thunder.

Same physics as the doorknob. The only difference is how much charge got separated and how far apart it got moved, and both differences show up as one number: how much work was done separating it, which is how much comes back.

The electrons crawl and the energy sprints

Here is the part that reorganizes the picture, and it is the bridge to the whole second question.

In a copper wire carrying an ordinary household current, the electrons do not race along. They drift — with a bias imposed on their otherwise random jostling — at a fraction of a millimeter per second. Depending on the load, a given electron needs somewhere between roughly fifteen minutes and eight hours to travel the length of your arm.

Yet the light comes on the instant you flip the switch.

The resolution is that the electrons are not what carries the energy. They carry charge. The energy travels in the electromagnetic field in the space around the wire, at a large fraction of the speed of light. Work this out carefully in classical electrodynamics — computing, at every point in space, how much energy is flowing and in what direction — and the answer is genuinely strange: energy flows out of the battery into the surrounding space, travels through the space alongside the wires, and enters the bulb through its sides. The wire’s job is to guide the field, the way a riverbank guides water without being the water.

The same thing is true of the spark. The electrons crossing the gap are the charge finally getting home. The energy that heats the channel and makes the flash was stored in the field the whole time — in the arrangement, in the space, not in the particles.

So: photons or electrons?

Both, and they are not alternatives. They are doing different jobs, and once you have the field picture the relationship between them is straightforward.

• Electrons carry the charge. They are what got displaced and what returns.
• The electromagnetic field carries the energy and the force. It stores the work you did and delivers it.
• Photons are what that field is made of. This is the quantum description of the same thing. When two charges push on each other, the interaction is carried by photons — virtual photons, meaning excitations of the field that exist only as part of the interaction rather than flying off as light. Saying “the field pushes them apart” and “photons carry the force between them” are the same statement at two resolutions.
• And some photons fly off as light — the ones emitted when excited atoms in the channel settle back down. Those are the only ones you see, which is exactly why they are the misleading ones.

The question “is it photons or electrons” quietly assumes the two are competing candidates for the same role. They never were. One is the thing that moved; the other is the thing that pushed it.

Energy is a number, not a stuff

Now the second question, and the reason it does not have the shape it seems to have.

Everything above can be described without ever treating energy as a thing that exists somewhere. Electrons moved. A field configuration changed. Air ionized. Photons were emitted. Energy never appeared in the story as an object — it appeared as an accounting: how much work it took to separate the charge, and how much came back out as heat and light and sound. The number at the start matched the number at the end.

That is what energy is. Not a substance things are made of, but a quantity things have, computed from their configuration and motion. A stretched spring has energy; the spring is made of steel. A moving car has energy; the car is made of metal and rubber. A charged cloud has energy; it is made of water and ice.

Asking what things are made of energy is like asking what things are made of momentum, or made of length. Those are all properties — real, measurable, essential to the physics — and none of them is a material. Energy feels different only because we talk about it as though it flows and gets stored and gets used up, and the metaphor is so useful in engineering that it hardens into an ontology.

The precise version. “Everything is energy” is false. “Everything has energy” is true and nearly empty. The interesting claim is a third one, and it is about fields — below.

Why there is such a number at all

The obvious follow-up is why this particular bookkeeping quantity should matter so much, if it is not made of anything. Why conserve that?

The answer is one of the most satisfying results in physics, and it is structural rather than empirical: every continuous symmetry of the laws of physics produces a conserved quantity. That is Noether’s theorem, and the correspondences are exact.

Energy is conserved because the laws of physics are the same tomorrow as today. That is the whole reason. Run an experiment now and run it next year, and if the rules governing it are identical, then there is a quantity you can compute from the state of the system that cannot change as it evolves — and that quantity is what we call energy.

This is why energy conservation is not a fact about a substance being neither created nor destroyed. It is a fact about time being uniform. Which makes energy less like water in a bucket and more like the balance in a ledger: absolutely real, tracks something true, and made of nothing.

The one place “matter is energy” is nearly literal

E = mc² is where the popular version comes from, and it deserves a careful reading rather than a dismissal, because there is something real in it.

First, what the equation actually says. It does not say matter can be converted into a substance called energy. It says mass and energy are the same quantity measured in different units. The c² is a conversion factor and nothing more, exactly like the 1609 in “one mile is 1609 meters.” Distance is not converted into meters. Mass is not converted into energy — it is energy, expressed on a different scale, and the scale factor is enormous, which is why a small amount of mass corresponds to a spectacular amount of energy.

Now the part that is genuinely startling. A proton is made of three quarks. Add up the masses of those three quarks and you get about one percent of the mass of the proton.

The other ninety-nine percent is the energy of the gluon field binding them together, plus the kinetic energy of the quarks churning around inside. Since mass just is energy content, that internal energy shows up on the scale as mass — as weight, as inertia, as gravitational pull.

You are made of atoms; atoms are mostly protons and neutrons by mass; and those are about 99% internal field energy and motion. So when you stand on a scale, the number is very nearly a measurement of how much is going on inside you rather than how much stuff you contain. If there is one place the intuition “matter is energy” earns its keep, it is here, and it is worth holding onto.

But note what that does not license. It does not mean the proton is a lump of energy that could have congealed differently into a photon. It means the proton is a particular configuration of particular fields, and the energy of that configuration is what we weigh.

What everything is actually made of

The common substrate exists. Here it is.

In the current picture, space is filled — everywhere, always — with a set of fields. Not a field around things, the way an electric field surrounds a charged doorknob; fields as the base layer, present in empty space, each one a quantity defined at every point in the universe. There is an electron field, a photon field (which is the electromagnetic field), a field for each flavor of quark, a Higgs field, and so on.

A particle is a ripple in one of those fields. An electron is a quantized excitation of the electron field — a discrete lump of disturbance in it, the way a note is a discrete mode of a vibrating string rather than an object sitting on it. A photon is a lump of excitation in the electromagnetic field. Two electrons are identical in every measurable respect not by coincidence but because they are the same kind of ripple in the same one field.

This is the claim the original question was reaching for. There is one substrate, and everything is a state of it, and different states give you different things. That is right. The correction is only about what the substrate is:

Energy is not the stuff. Energy is the measure of how much stuff is doing something.

Why more energy does not turn one thing into another

The last piece of the question was the ladder: different levels of energy giving you different things. This is where the substance metaphor does its real damage, so it is worth being blunt.

A photon with more energy is a bluer photon. Add more still and it is an X-ray, then a gamma ray. It never becomes an electron. What makes an electron an electron is not a quantity of energy — it is a set of properties belonging to its own field: electric charge of −1, spin ½, a specific mass, a specific way of coupling to the other fields. A photon has charge 0, spin 1, no mass. No amount of turning an energy dial converts one into the other, because energy is not the dimension along which they differ.

Even annihilation, the classic “matter into energy” case, is not what it is advertised as. An electron meets a positron and what comes out is two photons. Nothing became energy. The electron field’s excitations were converted into photon field excitations — matter turned into light — and energy is the number that stayed the same across the transaction. Energy was not a participant. It was the audit.

Where the intuition is right anyway

Having said that plainly: the sense that energy scale governs what can exist is correct, and it is important. It just works by a different mechanism.

Energy is the entry fee for making a particle. Because mass is energy, creating a particle requires supplying at least its mass-worth of energy. A photon carrying enough energy, passing near a nucleus, can produce an electron and a positron out of the vacuum. Below that threshold it cannot, no matter how many photons you have. So energy availability determines what is reachable, which is why colliders are described by energy — it is a statement about what is affordable, not about what raw energy congeals into.

And energy scale changes the rules themselves. The electromagnetic and weak forces are not actually two forces. Above a certain energy they are one force with one set of symmetries. Below it, the Higgs field settles into a nonzero value throughout space, that symmetry breaks, and the single force separates into the two we observe — the weak force’s carriers acquiring mass in the process while the photon stays massless. The early universe, hot everywhere, sat above that threshold; as it expanded and cooled it fell through, and the forces we have are what precipitated out.

So: high energy really does mean a different-looking world, with different particles available and forces that have not yet separated. But the mechanism is which fields are excited and which symmetries are intact, not energy thickening into matter as it cools.

What this leaves open

Three places where the tidy version above is genuinely unfinished, rather than simplified.

Energy conservation is a local law, not a cosmic one. Noether ties energy conservation to the laws being unchanging in time. In general relativity, spacetime itself is dynamic, and for an expanding universe there is no global time-translation symmetry to invoke — so total energy of the universe is not a well-defined quantity. This is not a technicality: light traveling across the expanding universe redshifts, losing energy, and that energy does not go anywhere. Locally, energy conservation is as exact as anything in physics. Globally it does not straightforwardly apply.

Nobody knows why the fields are the ones they are. The picture explains what things are made of but not why there are these particular fields with these particular masses and charges rather than others. The masses are measured, not derived.

The vacuum’s energy is the worst prediction in physics. Empty space, in quantum field theory, should have an energy density from the fields’ unavoidable fluctuations. Space does appear to have an intrinsic energy density — it is what drives the accelerating expansion. The two numbers disagree by many tens of orders of magnitude. That is an open problem sitting directly underneath the claim that fields are the substrate, and it says the account above is at best incomplete at its foundation.

Sources

• The Feynman Lectures, Vol. I, Ch. 4 — Conservation of Energy. The canonical statement that energy is an abstract accounting quantity rather than a substance, including the blocks parable.
• The Feynman Lectures, Vol. II, Ch. 27 — Field Energy and Field Momentum. Where the energy actually flows in a circuit, and why it enters a bulb through the sides.
• NOAA / National Weather Service — Understanding Lightning. Charge separation in storm clouds, stepped leaders, return strokes, channel temperature.
• The Ice Crystal–Graupel Collision Charging Mechanism of Thunderstorm Electrification. The temperature dependence of the charge transfer, and why storm charge structure is layered rather than a simple dipole.
• Particle Data Group. Quark and proton masses, for the ~1% figure.
• Noether’s theorem. The symmetry-to-conservation-law correspondence.
• The cosmological constant problem. The vacuum energy discrepancy noted at the end.