The direction of current is taken to be opposite to that of the flow of electrons, due to the established convention that current is in the direction of the flow of positive charges. My question is why didn't we just change this and redefine current as being in the direction of the flow of negative charges (i.e electrons). The best answer I could find on this site simply states that it would have been a bad idea to change the convention, but why is that so?
In typical metallic wiring, current flows in the form of negatively charged electrons.
In semiconductors (such as transistors in electronics or solar panels), current flows as either negative electrons and positive holes depending on type.
In plasmas (such as an arch from an electric lighter or fusion plasma in a power plant), current flows as both negative electrons and positive protons.
In electrolytes (such as the liquid within a battery), current flows as both negative and positive ions.
In general, current isn't necessarily about electrons. So there's no need to make the huge step of redefining centuries of consensus on the direction of current just to make it fit the electron flow direction.
I personally quite like the fact that most definitions of this sort are based on the positive version of what we are dealing with (current direction, voltage polarisation, electric fields and forces etc.). This is nicely consistent and easy to remember.
There are two complementary answers to this convention.
1. Even though electrons flowing through a conductive wire is the most commonly experienced form of electric current, it is not the only form.
Particle beams are also a form of electrical current. Whether the conventional current matched the particle motion depends on the charge of the particle. In the Large Hadron Collider (LHC), these directions match because the particle beam is made up of protons, which are positively charged. In the Stanford Linear Accelerator Center (SLAC), the beam is made of electrons, so the conventional current points backwards.
Plasmas have both kinds of charge motions. In a plasma--like the inside of a fusion reactor, a star, or a lightning bolt--the material is heated to such a high temperature that the electrons in atoms are liberated from the nucleus. So, electric fields accelerate the positively charged nuclei one way and the electrons the other way. The total current past any point is equal to the flow of positive charges one way minus the flow of negative charges the other way.
When working with semiconductors, it can be helpful to model them by thinking about the movement of negatively charged electrons and positively charged holes, which are places where electrons are absent in the crystals.
2. It is not good to change conventions without a good reason.
The definitions of scientific terms are chosen not just to make them simple enough to learn and use, but also to match the experiences of all past scientific work. If the definition of conventional current were changed today (June 22, 2021), then the scientific literature would be split into two parts: before and after June 22, 2021. That would force the reader of any scientific paper/journal/textbook to check the date of publication to see which convention was being used for that paper.
The issue bit me once for a different definition. I was reading a paper from 1963 (Achromatic Magnetic Mirror for Ion Beams, for the curious) to use the equations for simulation code I was writing. But, I was not getting the same results as the paper. I knew I was making some mistake since this was a highly cited paper and nobody had pointed out a mistake. Then, I noticed the statement: "the mass of the particle does not change." Huh? Why would the particle's mass change? I realized then that the author meant relativistic mass when he used the symbol $m$ in equations. Almost all physicists nowadays use $m$ to mean a particle's invariant mass. At that moment, I could reconcile the differences between my simulation and the paper's predictions.
Changing definitions makes reading historic science harder.
It probably would not make sense to do so, since electric current is not simply the motion of a bunch of charge. Instead, electric current is the net motion of electrically charged particles and the movement of electric field disturbances connected to the charges.
The objects that are really contributing to electric current are called charge carriers. Electric charge carriers are not always electrons nor are they all negatively charged. In fact, from that link
a charge carrier is a particle or quasiparticle that is free to move, carrying an electric charge, especially the particles that carry electric charges in electrical conductors. Examples are electrons, ions and holes. The term is used most commonly in solid state physics. In a conducting medium, an electric field can exert force on these free particles, causing a net motion of the particles through the medium; this is what constitutes an electric current.
Conventional current is simply taken as the flow of a positive charge from positive to negative and is taken as the direction reverse of real electron flow. This does not mean that conventional current is the opposite of net electron flow. Also, there are many examples where electrical current is exclusively the flow of real positive charge, like in a chemical battery where there is an internal current flow of positive ions from the anode to the cathode (positive plate), that is opposite in direction to the flow of electrons.
There are historical reasons (see the other answers).
But there is also a more fundamental philosophical reason:
Name are just labels. The question in science and more generally in society is not so much:
- « Is the label chosen for this object accurate, fitting, , intuitive, descriptive or not?»
As it is:
- As long as we all agree on what « red » or « round » or « 1 Km » or « 1 degree Celsius » or « 1 degree Fahrenheit » means, the choice of naming a concept this or that does not matter.
As long as the definition of an item is clear enough and univoque enough to generate unanimity, consensus, the particular choice for a given label does not matter.
Sometimes, however, the choice of a particular label or designation, although univoque can be a bit counterintuitive, unfortunate, and needs getting used to.
For instance, is is perhaps clearer to say that un unsuccessful company has lost money (e.g. on a given year), rather than to say that it has had a negative income during the same period of time (still, basically it changes nothing).
Electrical current is due to the drift of the electrons, that's true, so for current it might have been good if the moving particles were defined as positive.
But to change conventional current to the direction of flow of negative charge would really mean defining electrons as positive as the sign of electrical work done $W=QV$ is tied in with the sign of the charges and there would be repercussions throughout physics.
So the rest of the answer is to do with why electrons have been defined as being negative:
Long before electrical current was commonly used in everyday life, a choice had been made.
Benjamin Franklin was the one who first chose to call charge carriers negative. Franklin identified electric charge carriers after a series of rubbing experiments. He simply made a choice that made sense to him to call them negative.
Benjamin Franklins famous kite experiment was 1752.
Later on, at the end of the 19th Century, research was being done on other types of particles and radiation, e.g. alpha particles, the atomic nucleus, etc...
Two types of radiation were discovered by Rutherford from the radioactivity and named alpha and beta in 1899. The least penetrating, the alpha particle was found to be positive.
The electron had been discovered a few years earlier by J.J.Thompson (1897).
According to wikipedia:
"In 1900, Becquerel measured the mass-to-charge ratio (m/e) for beta particles by the method of J. J. Thomson used to study cathode rays and identify the electron. He found that e/m for a beta particle is the same as for Thomson's electron, and therefore suggested that the beta particle is in fact an electron."
To later change the sign of the charges, when electricity became more common, would mean lots of research in nuclear and atomic physics would have been confusing to the readers of that time and thereafter.
So it has become a convention that the electron is negative and the alpha particle, the nucleus (1911) and hence the proton is positive.