eli5: Why Do Magnetic Fields Point Clockwise Around a Current?

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As we know through experiment, the magnetic force around a current carrying wire always points in the same direction given the direction of current, and this direction is described with the ‘right hand rule.’ What is it about the universe that has this ‘preference’ for this, and only this, direction?

Or from a mathematics perspective, why are our electromagnetic vector coordinates the way they are, and not the other way around? It seems the direction of fields is axiomatic to the equations, and something we tack on at the end after calculating magnitudes. For instance, “we just used ampere’s law to calculate the force at this distance from the wire, now to know the direction, let’s use the right hand rule.” Nowhere in the math does it say that the direction is a necessity.

It seems to just be an observed fact, and we have to include this fact in our equations. But this fact is not derived from the equations. For context, I understand that the electromagnetic equations can be solved with either a right or left convention. My question does not pertain to this convention, but the underlying nature of the universe and its ‘preference’ to follow the same direction every time given a direction of current. If it’s said the angular momentum of the vector causes this direction, then still it remains why this direction and not the other?

It all seems so asymmetric and arbitrary.

In: Physics

11 Answers

Anonymous 0 Comments

I will paraphrase a joke that I heard: “Excellent question! Next question, please”.

“Why?” is the reason that we have scientists, explorers and philosophers. Surely there must be a reason, something that explains life and all that we can observe. And, over generations, we have observed and recorded certain behaviors. And for each observation, if we have enough evidence, we can formulate a rule or formula. And someone will invariably ask, “I’m not asking WHAT, I’m asking WHY. Can’t you give me a simple explanation?”

Well . . . no. For physical and biological sciences, the deeper we explore the more complicated it gets. (But why?)

At the smallest and the largest ends of the scales, the answers sometimes make little sense, but the math seems right. Quantum hoodoo. There are larger and smaller and yet unknown factors. (But why?)

Penultimately, if you ask someone to “explain it like I’m five”, depending on the question, the best answer is “because it is”. (But why?)

And ultimately, for five year olds, we answer, “Because I said so, now go to bed!” (But why?)

Not to mock you for your very good question, of course. The answer seems to be, “We know the WHAT pretty well, and it’s complicated, but we’re still working on the WHY. Check back every decade or so.”

I’m not a physicist, so the WHY question that you asked may actually have an answer. I’m pretty confident that the simplest explanation isn’t a kindergarten level, but a grad level thesis.

It may be simpler to ask “Why is there life?”

Imma say, “Good question, I’ll ask your mother. Now go to bed!”

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