This article is a companion material to the Course COM 25100 Information, Technology, Society which I teach at Purdue University as a University core class. The course teaches trade-off thinking as a fundamental method for understanding technological choice and innovation.
Where does electricity come from?
You watch TV. You listen to music. You receive a phone call. You connect to the Internet over a WIFI connection. All of these actions are powered by electricity. But what does electricity precisely do? What can’t it do? How does the use of electricity as a fundamental medium of communication limit what we can and cannot do?
While WIFI, cellular networks, or broadcasting TV sound like very sophisticated technologies, they all rely on a straightforward trick, which has been with us since the creation of the most elementary electronic telecommunication systems, which was the Morse telegraph and its predecessors. This is the ability of electricity to produce magnetism and vice-versa. In fact, electricity and magnetism are the same things! Electric power is one of the four fundamental forces of nature. The other three are gravity and two more invisible forces that can only be observed within some sub-atomic particles. Conventionally the last two are called the weak and the strong atomic forces. (NB, gravity is not the same as magnetism).
If midichlorians are responsible for any, all, or none of these forces, I honestly do not know. What I know, however, is what electromagnetism is: the fabric of nature. Electricity exists in every single atom. It is, in fact, what makes the electrons and protons you learned about in school special. You might imagine these two particles as little billiard balls spinning inside and around the nucleus of the atom but, in fact, both are clouds of electric energy. Electrons are charged negatively, protons positively.
When electromagnetic energy manifests itself, it does several things. First, it can release its energy as spectacular explosions. This is what happens when you short a light or when lightning hits a tree. More subtly, you might observe that in electrically charged situations (such as a storm), hairs start standing on an end. This is because the strands of hair are electricity laden, which makes them magnetic, which makes them reject each other.
All electrically charged objects can attract objects charged with the same energy, since, remember, electricity is magnetism. More important, objects that are magnetic can be used to produce electricity. All electric power plants do is to spin magnets inside wire coils. That is where electricity is coming from. You can replicate this by moving a magnet through a coil of copper wire.
How do we use electricity to move things at a distance?
The truly, really cool thing about the free conversion of electricity into magnetism and vice-versa is that we can make things DO (move, change, act) other things at a great distance just by generating and sending electricity to remote locations. The action will travel at speed light, a detail I will explain in a minute.
How does electricity make things move at a distance, again? Well, if electricity is magnetic and because magnets can move other things, you can move those things using electricity. With sufficient sophistication, such actions can be combined with large power sources to reach very far. There, we can replicate anything a human can do with his or her hands: move, stop, grab, release, carry, even fly. You are very familiar with this idea. Any remote controlled vehicle, from a toy car to a military drone uses the trick of turning electricity into magnetism to control and change the state of objects at great distances. In the case of a toy car, when you push the “forward” button on the remote, an electric current is sent to the car, which charges a device, which becomes magnetic, which closes a circuit that engages the engine. The same happens when you turn the wheels, and so forth.
Now, the beauty of electromagnetism is that you can do the reverse to generate electricity. Electricity is the product of moving magnets over or through loops of wire. Kinetic energy (physical movement) displaces electrons, which carry electric charge, which is captured by the wires, which become electric.
Radio waves and electricity are the same things
In all I said so far I spoke about electromagnetism and electricity as if they were the same thing. Moreover, I also said that electricity can travel through the air, creating magnetism at a great distance. Your everyday experience tells you, however, that electricity travels through wires. When I say electricity, you might think that I am talking about the power that comes out of an outlet and only about that. At the most, you might allow that I am talking about the power that travels through telephone wires and electronic circuits.
That which travels through the air, as in my example of the remote controlled car, you might’ve thought as a different force or “thing,” namely radio waves. And you were right. But what you did not probably know is radio waves and electric power are in fact the same exact thing. You heard me right. Even more so. ALL radio waves are electricity (or more specifically, electromagnetic radiation). Not only the radio waves that control remotely operated toys are electricity (electromagnetism) but those that send us television, radio, and cell phone signals. It is all electricity, all the time.
Get ready to be even more surprised. The light we get from the sun is, in fact, a type of electromagnetism, too! It just happens to be visible to the naked eye. Light is produced by nuclear reactions that release electromagnetic radiation on a large scale. The X-ray waves that doctors use to look at our bones are electromagnetic (and a lot of them are produced by the sun, too). The deadly radiation that is put out by the nuclear bombs is electromagnetic, too.
How is this possible? Well, again, as I mentioned, electromagnetism is everywhere. It is present in all forms of matter since it is part of the most intimate fabric of the universe, which is made of elemental particles, electrons and protons. When a nuclear bomb explodes or when the sun boils over its own nuclear reactions (the same thing), the electric energy locked in the atoms of uranium, plutonium, or hydrogen is released as electromagnetic radiation in a bewildering array of kinds. Which brings us back to the idea that electromagnetism is one of the binding forces of nature.Electromagnetism both within the particles and outside them exists in a particular state of nature, called a field. To make it simple, let us call it a state of “radiating field” or simple, as a form of radiation. When exploding out of nuclear bombs or when generated by our TV stations, electromagnetism starts traveling as a never stopping radiating field of waves.
Electromagnetism: wave with frequency
At the same time, electromagnetism is not, in fact, a “thing,” like water, let us say, which is stable, quiet, and contained until released. Electromagnetism is vibrating energy that literally charges all things, all the time. These vibrations are sometimes weak and sometimes strong. Sometimes they can travel far, sometimes they can only go as much as a millionth of an inch. What makes the difference is the frequency of each type of wave. Typically, the electromagnetism contained in matter travels very little because, as you will learn later, it has a high frequency. Yet, it is there all the time, buzzing and beaming inside our own bodies, in the air, in rocks, and in specks of dust.
To understand why electromagnetism is, in fact, a type of ever-present wave, you should imagine it as a fundamental ripple in matter, the way a wave is a ripple in water. A water wave is mechanical energy; it is the shock or push of some event exercised on the water. However, the wave is not the water itself. It is the energy carried by water. As soon as the water hits an obstacle, the energy is expended, sometimes damaging the object it hits, and the wave disappears. The energy is gone, too. The same with electromagnetic energy. It is in all things, making them what they are. When you expend it, you simply push out energy from an initial source through matter and then through pure space, with no material support.
You heard it right. The fascinating thing about electromagnetic energy is that, unlike kinetic waves carried by water, it does not need a support to travel. Electromagnetism is its own support. That is why you do not need wires to broadcast electricity (radio waves). You can simply send it out, even in the interstellar vacuum.
This type of self-sustaining wave (energy) shares with all waves two features: frequency and wavelength. In other words, moving in pulses, electromagnetism has peaks and troughs. The number of peaks and troughs within a unit of time (second), defines the FREQUENCY of the wave. The higher the number of peaks and troughs, the higher the frequency. At the same time, the higher or lower the frequency, the greater the distances between two peaks increases or decreases. In short, electromagnetic waves can come in various frequencies and corresponding wavelengths. The basic unit of measurement for frequency is the Hertz or Hz. A wave has a frequency of one 1 hertz when it cycles once a second. In other words, it takes a second for the wave to peak twice. Since all electromagnetic waves travel at the speed of light (which is electromagnetism), the length of a wave with a frequency of 1 HZ is… the distance travelled by light in a second = 300,000 km or 186,000 miles. Electromagnetic frequencies start from 0 and go to observable frequencies 1014 (ten followed by 14 zeros) Hz. There are higher theoretical frequencies, but those were never observed. As frequencies increase, we use kilo, mega, giga, tera, peta, and so before Hertz to make the numeric notation simpler. A megahertz (MHz) is one million Hertz, a giga, a billlion, and so on.
The tradeoffs of electromagnetism
The inverse relationship between frequency and wavelength leads to a significant tradeoff in using electromagnetism. In electromagnetic fields, each wave is also a pulse of energy. When you have many waves in close succession, the frequency is very high and the energy carried by the electromagnetic radiation is correspondingly high. Yet, as you remember, waves of high frequency has very short wavelengths. The trade-off that obtains is between energy load and capacity to travel (reach). Why is this so? Although electromagnetic waves can travel through the vacuum, they cannot easily travel through solid materials. Or, they can if the wavelength of the radiation is sufficiently long to allow the wave to jump over it. Thus, some radio waves with very long wavelengths (yards or even miles) travel far. Radio waves with very short wavelength (typically millimeters or much shorter) bounce off obstacles or, even more dangerously, are absorbed by the obstacles. As short wavelength also have high energy load, due to high frequency, they can have lethal effects. This explains why X or gamma and beta ray radiation is lethal for the human body and radio waves are not. The wavelength of the former is microscopic, being absorbed by our body. The length of the former is macroscopic, jumping over us and anything smaller than a few yards and feet in size.
Another tradeoff found in electromagnetism is between reach and information load. To understand this, we need first to know how radio, telephone, or television transmission stations use electromagnetism to send out their signal. Roughly, they encode the information to be sent out as variations in the frequency of the signal. In essence, each bit of information (sound, number, letter, shade of color or light) is assigned a given frequency (at least in the analog communication world). Changing the frequency of the signal using a transistor and a capacitor (among other things) encodes specific units of communication. At the other end, the frequency is similarly decoded and turned into meaningful information. If you have a lot of information, you need many different frequencies to send the information. For this purpose, signals that have naturally very high frequency are better. If you have less information, you will use signals with low frequency. This leads to the conclusion that you can communicate a lot if you do not want to reach very far and that you will need to limit the amount of information if you want to communicate very far.
For, example, most HD television signals use signals with millions of cycles (waves) per second. At the same time, radio waves for talk stations (AM) use only thousands of waves per second. This makes the wavelength of the HD stations much shorter (meters) compared to that of the radio stations (kilometers). This is why you can listen to an AM station from Chicago in West Lafayette, Indiana, which are separated by 100 miles of distance, but you cannot listen to the FM radio stations from the same time.
Even more significant, the radio signals we use to connect to the Internet (the so call WIFI signals) have an even higher frequency, which is the billions of waves per second. This allows pushing out and absorbing a lot of information. However, these signals, unless they are amplified a lot can only travel short distances. This makes them hard to use for long distance communication but ideal for local, intense communication.
In conclusion, radio communication is by design made for local, high-quality communication. It is not very good for long-distance communication. That is why, maybe, we have not yet heard from aliens. Encoding a very complicated message and sending it over light years of distance is not easy.
A final tradeoff that comes with communication technologies is that between information variety and bandwidth. Each signal stream demands a particular frequency. In fact, because we vary the frequency for each component of the signal, we need a specific band of frequencies to create a communication channel. In radio broadcasting, each FM station gets a channel or band in the MHZ area of the spectrum. This means that each radio signal cycles millions of time a second. The spread of stations is between 88 and 100 MHz. Each station gets a carrier wave at a certain point, typically a fractional number, such as 99.8 MHz. However, what the station gets is not only the right to broadcast on that frequency but to send out signals that can vary .2 MHz (or 200 KHz) around the fixed carrier frequency (BTW, this is why the station numbers are always even). Thus, when you tune into a station broadcasting on the 99.8 MHz band, you may, in fact, receive a signal that is anywhere between 99.9 or 99.7 MHz.
Thus, at any given point in any given place, you cannot broadcast more than a finite number of signals. In other words, the number of radio stations allowed to broadcast in a given area is restricted and pretty low. The practical number of channels that can be crammed in a given area is, in fact, lower than that of frequency bands allowable. Receivers, just like the human ear, needs to accept all signals and only after that to decide which individual one to attend to. If two signals have very similar frequencies or if two transmitters use very similar frequencies, you get what is called interference. It’s the same effect with many peoples speaking at the same time at a cocktail party. You hear different voices talking, but you cannot understand what each is saying. This is why governmental regulators (in the US, the FCC) determine how many radio or television stations can broadcast in a specific area. The frequencies are allocated in such a way that the distance between the frequencies is at least 4 bands (800 KHz or .8 MHz). Thus, if in a market you have an FM station broadcast on 95.2 MHz, the next station will broadcast on the 96 MHz channel.
This simple tutorial, complemented by the readings listed in the links, are meant o help you better understand what electromagnetic communication is and how it works. If you then read the Andrew Wheen’s book, from Dot-Com to Dot-Dash, you will also understand how the tradeoffs I discussed shaped in many other ways the future of telecommunication as well.