Imagine the following conversation: One man asks another: “Pardon me, sir, but do you know what an alusisa is?” “Oh yes, silly,” the second man answers. “Alusisa is what skeemoids carry. Everyone knows that.”
Now this answer would not help our curious questioner very much, would it?– especially if he did not know what the heck a skeemoid was.
A very similar situation arises when talk about electrical charge. People answer that charge is what an electron carries, silly. But in truth, this tells us very little about what charge actually IS– especially when one considers that the fundamental nature of electrons is still quite mysterious to us, too.
Physicists have been trying to figure out charge for a long time. For awhile, many scientists thought that an electrical current consisted of two subtle fluids, one positive and one negative, and people like Coulomb, who lived mostly during the 1700s, imagined charge as the imbalance of these electric fluids. This excess amount of one particular fluid could produce either a positive or negative charge, depending on which electrical fluid was in excess.
Faraday, on the other hand, believed that there is only one type of charge, and that there is actually no repulsion between charges, only different degrees of attraction. He also did not buy the “two electrical fluids” theory.
Faraday thought that what we perceive as electricity is the movement of lines of force through a conducting body. The so-called positive and negative sides of a current are actually just different ends of the same lines of force. This is why charges ALWAYS come in pairs. There is no such thing, said Faraday, as a stand-alone, or “absolute,” charge with the quality of being either all positive or all negative.
Faraday knew that some materials conduct electricity better than others. If a material is not particularly good at conducting electrical lines of force, a stress can be built-up. This stress is what we call charge.
Faraday imagined that the molecules in a material become polarized by an electric current attempting to pass through it. In other words, part of each molecule becomes relatively positive and the opposite end becomes more negative. The greater the polarization, the greater the strain on the material becomes. The molecules will exist in this state of tension until the pent-up strain, or “charge,” can be released (dis-charged). For Faraday, the produced current or spark is the breakdown of this built-up stress.
Maxwell had a very similar view to Faraday’s, only Maxwell did not think the build-up of stress was due to molecular polarization. He thought the molecules in a material under electric stress became physically distorted. These distorted molecules would press against each other, creating a physical pressure. The worse the distortion grew, the greater the charge would become.
Maxwell believed that the distortions are caused when the electrical current flowing into a material is greater than the current flowing out.
Lorentz gave us the basis of our modern view of electricity. He said that charge was not due to excessive fluid build-up, or to induced polarizational strain, or to induced physical distortions. Instead, Lorentz contended that extremely tiny particles carry electrical charge, and that a charge builds up when there are too many particles of the same sign. Most people today would call these tiny charged particles “electrons” and assign them a “negative” charge; there are also many people who claim that positively charged counterparts to electrons exist, and they call these critters “positrons.”
Of course, none of this answers the fundamental question: what IS charge? That is to say: sure, you can say that electrons carry a negative charge, but what in blazes IS a negative charge? Some kind of fire? Some kind of particle shape or orientation? Is it some special characteristic of mobility? of adhesiveness? of repulsion?
As smart as we like to think we are, and as complacent as we can be about our view of the universe… “charge” is still a mysterious force of the cosmos.