Where Did the Electrons Go?

Where does electricity come from? I knew that electricity generated at power plants travels through copper wires to our homes. Thermal power plants burn oil or coal, nuclear power plants split atomic nuclei, and hydroelectric power plants use water falling from a height. These different energy sources are used to turn turbines. Electromagnetic induction occurs in the generators connected to those turbines, and the electricity produced is delivered to homes through transmission lines. So far, this was not difficult to understand.

But where do power plants get their electrons? Do they strip electrons from around atomic nuclei and send them through copper wires? No. Copper wires already contain electrons that can move freely. A generator does not create or supply those electrons. It produces voltage through changes in a magnetic field. Then do the electrons in the copper wire travel all the way from the power plant to our home? No again. In the alternating current used in homes, electrons mainly move back and forth near their original positions. The electrons at the power plant do not make a long journey to our home.

An analogy came to mind. People are standing in a line. The person at the back pushes the person in front, who then pushes the next person. In this way, the force is transmitted all the way to the person at the front. The people themselves do not travel far. What is transmitted is the effect of the movement. Is electricity like that? The phenomena are not exactly the same, but the analogy was useful for distinguishing the long-distance movement of electrons from the transmission of energy. In an actual wire, electromagnetic fields play an important role.

At that point, I remembered a film I had seen long ago. It was Fallen (1998), starring Denzel Washington, released in Korea under the title Dark Angel. The film features a demon named Azazel. The moment he comes into contact with another person, he moves into that person. Even when his host changes, the demon retains his identity. I still remember the scene accompanied by the Rolling Stones’ song Time Is on My Side. Could electrical energy move in a similar way?

This analogy led me to think of electrons and energy as separate concepts. An electron is a particle, while energy is transmitted. It is not that electrons travel from the power plant to our home, but that energy is transmitted through interactions between electrons and electromagnetic fields. Then are electrons not consumed? That is right. An electron does not disappear because it has powered a vacuum cleaner’s motor. Electrons continue to exist, while the vacuum cleaner converts the electrical energy it receives into motion and heat. What we pay for on our electricity bill is not the use of electrons but the amount of energy supplied through the power grid. Having understood this much, a new question arose. What exactly is energy?

Burning oil produces heat. That heat boils water, and the steam turns a turbine. Water falling from a height turns a turbine, while sunlight is converted into electrical energy by solar panels. Energy is heat, then motion, then electricity, and then light or heat again. It seemed to change its form and continue to exist, much like Azazel. Then is energy matter? Is it a particle? Or is it some kind of substance contained within matter?

Physics offered an explanation different from what I had expected. Energy is not an independent substance but a quantity that describes the physical state of objects and fields. A moving ball has kinetic energy, and water at a height has potential energy. This is not because energy exists inside them as a separate substance, but because their states of motion, position, and interaction differ. I could understand the explanation, yet it still did not feel intuitive. I felt that matter ought to have a form. Even if something had no form, would there not have to be something that existed in order for it to have a state?

This was where the concept of the electromagnetic field appeared. An electromagnetic field can interact with charged particles and transmit energy. Even more surprising was the fact that electromagnetic waves can propagate through a vacuum where there are no electrons. The sunlight that crosses space to reach Earth is explained by the same theory of electromagnetism. Electricity and light were connected phenomena. Then what is a photon, the particle that makes up light?

A photon is different from an electron. Nor is it a composite particle made of quarks, like a proton or neutron. In current physics, it is classified as an elementary particle whose internal structure has not been discovered. The electron is also an elementary particle. Up quarks, down quarks, strange quarks, and charm quarks are elementary particles as well. But does calling something an elementary particle mean that it truly cannot be divided any further? Or does it mean that human technology has not yet discovered a smaller structure? Humanity once believed that atoms could not be divided any further. Later, the atomic nucleus and electrons were discovered, followed by the quarks inside protons and neutrons. Then might the particles we now call elementary also be found to have internal structures someday? That possibility remains open. There are attempts, such as string theory, to explain particles as different vibrational states of something more fundamental. These have not yet been experimentally confirmed.

In the course of explaining photons, an even stranger expression appeared: “a quantum excitation of the electromagnetic field.” What is quantization? What is an excitation? Quantization means that certain physical states or exchanges of energy can occur in discrete units rather than taking continuous values. An excitation means being in a higher-energy state than a lower-energy state. A photon could therefore be understood as a quantum state in which one unit of energy is added to a particular vibrational state of the electromagnetic field. But is this the ultimate reality of nature? Or is it a way of explaining nature that humans have devised after observing it? Natural phenomena existed before humans discovered them. Quantization and excitation are concepts humans developed to explain those phenomena. The fact that a theory makes accurate predictions does not guarantee that the way it describes nature represents nature’s final form.

My thoughts returned to the form of particles. An electron is said to have mass. That mass can be expressed in kilograms. It is an extremely small number, but it is certainly not zero. Then what does an electron with mass look like? Current physics measures the electron’s mass, charge, spin, and other properties with great precision, but no intrinsic spatial size or internal structure has been discovered. Physicists explain that the existence of mass does not necessarily imply the existence of volume or a surface. Yet the explanation left me with another question. The word mass itself makes us imagine a lump of matter with a definite form.

Then what do particle physicists actually observe to confirm the existence of a particle? In particle accelerators, particles are made to collide at high energies, and scientists analyze the traces left by particles produced in those collisions. They measure trajectories, energy, momentum, and other quantities, then infer the types and properties of the particles from the results. The lines and curves we see in photographs and videos are not the physical outlines of the particles themselves, but traces they have left behind or reconstructions of detector records. Instead of seeing the faces of particles, humans were discovering their existence through the actions they left behind.

Today’s questions began with where electricity comes from. I asked whether power plants produce electrons and where those electrons go. When I learned that electrons are not consumed, I began asking what energy is. Trying to understand energy led me to electromagnetic fields, then from electromagnetic fields to photons, from photons to quantization and elementary particles, and finally back to the questions of form and mass. Questions and answers followed one another, much like a Socratic dialogue. An answer did not bring the questioning to an end. Instead, it revealed problems I had never considered before.

I learned that electrons do not disappear when electrical energy is used, and that energy can be transmitted through electromagnetic fields. Energy is not a separate substance but a physical quantity that describes the states of objects and fields. But why does energy exist? What, ultimately, is a physical state? Is the electromagnetic field the final reality of nature, or an expression of a deeper structure we have yet to discover? Today, I set out to understand how electricity flows and ended up asking what matter and energy are. Heraclitus said that everything flows. Through today’s questions, I found myself thinking about those words a little differently. Perhaps it is not everything that flows, but energy.

But if energy flows, where does it flow from, and where does it flow to? Where does the energy that has flowed away remain? Following these questions, a familiar statement began to sound strange again. Energy is conserved. We learn this at school and use it in everyday life as though it were self-evident. Energy, we are told, is neither created nor destroyed but merely changes form. Even when electrical energy becomes kinetic energy and kinetic energy becomes heat, the total energy is conserved. But how far has this law been proven? Have humans confirmed that none of the energy in the universe has ever disappeared?

Physics has tested the law of conservation of energy through countless experiments. In particle collisions, chemical reactions, and the conversion of heat into motion, the conservation law holds with great precision. There is also a mathematical explanation connecting the symmetry of physical laws over time with energy conservation. In general relativity, energy and momentum are conserved locally. But this does not mean that we can define the total energy of the expanding universe as a single number and say that it always remains constant. We apply laws verified in laboratories to the distant universe. That is a scientific judgment supported by substantial evidence. But have we also confirmed that those laws hold without exception at every place and every time in the universe? I was not claiming that the existing laws were wrong. I wanted to know where the boundary lay between what we had actually verified and what we believed on the basis of those observations.

I returned to a single photon. Suppose we build a perfectly sealed room lined with mirrors and fire one photon into it. The walls do not absorb the photon at all, and no energy is lost when it is reflected. The photon would travel from one wall to another, then back again. If those ideal conditions continued indefinitely, the photon could keep reflecting. But now I decided to make the room a little different. Suppose it is a room measuring ten meters by ten meters, in which extreme time dilation occurs. Let us imagine that, according to an outside observer’s clock, it takes the photon one hundred billion years to reach the opposite wall. This does not mean that the photon actually moves more slowly than light in its immediate surroundings. It is a thought experiment in which gravitational time dilation is extended to an extreme so that the photon’s movement appears extraordinarily slow to an outside observer.

Now ten billion years have passed. According to the outside observer, the photon has still not reached the opposite wall. It has not reflected from a mirror even once. Yet if we assume that we can somehow continue to confirm its existence, the photon is still inside the room. The small size of the space and the possibility of observation give us confidence. This time, we fire a photon into space. Suppose it travels for ten billion years without colliding with any matter. Because it is now far from its point of origin, we cannot continue tracking it. Then what is the difference between the photon in the mirrored room and the photon in space? Neither has yet reached its destination, and both are still moving. One is close enough to observe, while the other is too far away.

Of course, the physical conditions of the two spaces are not entirely identical. Unlike the ideal mirrored room, the actual universe is expanding, and its gravitational field is not uniform. A photon traveling through space may also lose energy through redshift caused by cosmic expansion. But what I wanted to compare was not the properties of mirrors. My question was whether the continued existence of a photon confirmed in a small, observable space could be assumed in the same way in an immense space that we cannot fully observe.

My thoughts then turned to ancient starlight. We observe light that has traveled for more than ten billion years before reaching Earth. But has that light retained its original state throughout the journey? Suppose a supernova explodes and sends one hundred photons toward Earth. How can we know whether one hundred, ninety-nine, or fifty of those photons actually arrive? The condition that they are traveling toward Earth is important here. I was not asking why only a tiny fraction of the light reaches Earth when starlight spreads in every direction. I was assuming that one hundred photons had set out from the beginning along paths that would bring them to Earth. Could we then determine how many of them actually arrived?

Astronomers estimate a light source’s original brightness and compare it with the brightness observed. They analyze the effects of distance, absorption and scattering by cosmic dust, and redshift caused by the expansion of the universe. They also compare distances inferred from supernova brightness with distances measured independently to test for unexpected photon loss. There are, in other words, ways to compare observations with theory. But this is not the same as directly counting one hundred photons at the moment of emission and then counting the arriving photons ten billion years later to compare them one by one. Current observations can be explained by known interactions and standard physical laws, and no phenomenon in which photons disappear for no apparent reason has been confirmed. Photons are not regarded as particles that simply vanish because a long time has passed. Nor have we individually verified the fate of every photon traveling through the universe.

There was another problem. The disappearance of a photon and a decrease in its energy are not the same phenomenon. In an expanding universe, a photon can lose energy through redshift without being absorbed by matter. As its wavelength increases, its energy decreases. Then where does the lost energy go? In general relativity, the treatment of energy conservation across the expanding universe is not as simple as the treatment of a closed physical system in a laboratory. Eventually, I returned to the original question. Is energy conserved? The physical laws we know provide substantial grounds for saying that it is. Yet we cannot treat the entire universe as one perfect mirrored room and account for every photon and every unit of energy inside it. The extent of the universe we can observe is not the same thing as the boundary of the universe as a whole.

All these questions were connected to the process of conceiving a new novel. One of the starting points of A Dictionary of Galactic Extinction was a very simple assumption. What if a single photon disappeared without interacting with anything? It had not been absorbed by matter, converted into another particle, or carried beyond the limits of observation. A photon had actually vanished in a way that known physical laws could not explain. This was not a phenomenon confirmed by current physics, but an assumption made for the novel. And if that assumption were shown to be true, one of the fundamental laws through which humans understand the universe would have to be reconsidered.

I was not trying to calculate how much energy would be lost through the disappearance of a single photon. The energy carried by one photon can be extremely small. Its disappearance would not immediately bring the power plants and spacecraft of a galactic civilization to a halt. What interested me was the possibility that such a tiny event could undermine a civilization’s certainty about the world. Civilizations develop technologies based on the laws they have discovered, and organize their societies around those technologies. Countless people rely on those laws without personally understanding why they hold. Then one day, in a world where everything seems to be functioning reliably, an observation indicates that a photon has disappeared. At first, scientists might suspect a measurement error. They would replace their equipment and repeat their experiments. But what if the unexplained deficit remained?

What that civilization would then face was not merely the problem of a single photon, but a question about the universe it believed it understood. That question might not remain confined to scientific laboratories. Governments and corporations, religious institutions and the media, politicians and ordinary citizens would begin making different judgments. What should be disclosed, and what should be concealed? What should be considered dangerous, and who should be protected? How would humans choose to act when confronted with a phenomenon whose cause remained unknown?

A Dictionary of Galactic Extinction began with questions like these. The disappearance of a single photon creates a small crack in the foundations of galactic civilization. Faced with that crack, people act according to their own judgments and good intentions. The consequences of those choices unfold in the novel.

Today, I set out to discover where electricity comes from, then asked what electrons are, what energy is, and whether energy is truly conserved. Those questions eventually led me back to the starting point of a novel I had been imagining for a long time. In the beginning, there was a single photon. Its disappearance alone would not cause an entire galaxy to collapse. What matters is what people come to believe and what choices they make after that event.