Why did we decide one side of a magnet or proton was a “positive charge” and the otherside of a magnet or all electrons were “negative” charges?


Would it matter if we all just decided one day to switch them and say all protons were negative and electrons were positive?

In: Physics

This doesn’t apply to magnets. They have magnetic poles, not positive and negative charges.

But as for electric things: the decision was arbitrary and was based on a guess. Many people today think it would have been clearer to do it the opposite way.

The label of positive and negative are as arbitrary as the label of x and y on a set of axes. But the general idea that these labels COULD be switched (as long as this switch was applied universally – ie “globally”) with no effect on the physics implies that there is a certain symmetry in the way the universe “thinks” about positive and negative charges. This type of symmetry (which Lawrence Krauss attempts to explain in #938 of the Joe Rogan podcast) is covered under the umbrella of Gauge Theory.

It may seem trivial to just switch the way we talk about positive and negative charges (and all other physical properties that share this type of Gauge symmetry), but this extends beyond just language to the way the universe is organized. When you use Cartesian coordinates to locate an object in the universe with the x-axis one way and the y-axis the other way (and the z-axis the third way, b/c the space in 3D), you designate that object a set of coordinates for its location in space. If we switch the axes and now say the x is the y and the y is the x, the location of that object has changed, even though it has not moved.

Of course this is only really makes sense in the context of the universe if we apply that same change to all objects in the universe. That is, to look at the universe as a coherent system, we need to be using the same set of axes all the time so we can talk about objects relative to each other. But there is nothing PHYSICALLY special about using one type of coordinate system over another.

This doesn’t just apply to coordinates, but this whole concept is pretty car outside of my expertise. From what I understand, electric charges are similarly arbitrary. Of course we can just start calling negative charges positive and vice versa, but if the universe actually wanted to instantaneously make all negative things positive and positive things negative, physics would remain in tact and nothing would change. But again, this would have to be done to the ENTIRE universe to maintain that symmetry.

For protons/electrons the answer is that is what Benjamin Franklin decided it should be.

Back in the day Benjamin Franklin discovered that if he rubbed a glass rod with silk and a rubber rod with fur while hanging those rods from string, the rods would attract each other. However if he hung two glass rods and rubbed them both with silk they would repel. He didn’t understand the specifics of what was going on but he puzzled out that there was something (charge) being added/removed from the rods, and that like charges repelled and opposite charges attracted. He arbitrarily decided that the glass rod would be the positive charge, this set the convention for charge. It turns out that the glass rod rubbed with silk was missing electrons which means that the electron was negative.