# Does nature behave according to the right hand rule?

jaydnul
I already know that the right hand rule could just as well be the left hand for the rotational motion vectors like torque and angular momentum, but what about magnetism? It seems like nature behaves strictly "right handedly" for magnetism. Is that true, or could you use the left hand rule, just as long as you were consistent with it?

Gold Member
2021 Award
You can use whatever convention you wish as long as you remember to point your fingers the way nature works

Mentor
2021 Award
A left hand rule for EM would work just as well.

jaydnul
Well this is where I'm confused. If I did an experiment where I shot a proton from right to left, through a uniform magnetic field that is pointing downwards (the north pole is above the proton, the south pole is below), the right hand rule would tell me that it would force the proton towards me, away from the screen. If I use the left hand rule, it says the proton is forced away from me, into the screen. But if I actually did the experiment, I would find that it went either one way or another, right? So only one rule could be valid. Where am I going wrong?

Mentor
Well this is where I'm confused. If I did an experiment where I shot a proton from right to left, through a uniform magnetic field that is pointing downwards (the north pole is above the proton, the south pole is below), the right hand rule would tell me that it would force the proton towards me, away from the screen. If I use the left hand rule, it says the proton is forced away from me, into the screen. But if I actually did the experiment, I would find that it went either one way or another, right? So only one rule could be valid. Where am I going wrong?

How did you decide which pole is north and which is south?

jaydnul
Oh ok, so the poles are arbitrary? Why do they say that on earth, the north pole is really the south magnetic pole? Why would that matter if it were arbitrary?

Mentor
Oh ok, so the poles are arbitrary? Why do they say that on earth, the north pole is really the south magnetic pole? Why would that matter if it were arbitrary?

Long ago, before we understood about opposite poles attracting and matching poles repelling, we observed that one end of a magnetized needle would reliably point to the the left when we were facing the rising sun. Because we were already in the habit of calling that direction "north", we naturally called that end of the magnetized needle the "north" end. Then when we learned about magnetic poles and opposites attracting, we realized that the end of the needle that we called "north" was being attracted to and pointing towards a magnetic pole that we called "south" even though it was at the earth's north pole.

Nick O
Oh ok, so the poles are arbitrary? Why do they say that on earth, the north pole is really the south magnetic pole? Why would that matter if it were arbitrary?

The definitions of the poles is arbitrary, but we do need to be consistent and differentiate between them. As long as all north-seeking poles have the same name (be it north, south, positive, negative, or gloop) and all south-seeking poles have a different name, we are fine.

The right-hand rule focuses on positive charges and north-to-south field lines; a left-hand rule using the same fingers and motions would focus on negative charges or south-to-north field lines.

Mentor
2021 Award
Oh ok, so the poles are arbitrary? Why do they say that on earth, the north pole is really the south magnetic pole? Why would that matter if it were arbitrary?
The label that you attach to poles doesn't really mean much. What is important is the direction of the magnetic field. If you switch your handedness from right to left then you reverse the directions of your magnetic fields. The reversed direction of the magnetic field and the left-handedness of the force law gives the force in the same direction.

EDIT: I should have read the responses first, looks like I am just echoing Nick O's post!

Nick O
You put it more clearly and simply than I did.

Imabuleva
Nature abhors a change in flux (at least when it comes to E&M). Nature will "create" electric currents such that the change in magnetic flux through all open surfaces is zero. This is, of course, the premise behind all modern electricity generation. Spin giant magnets near wire loops or wire loops in magnetic fields and you induce an EMF in the wire loop. Somehow, you have to provide the spin though!