Hey Crazies.
We’ve all played with magnets before, right?
The way they attract each other seems like
magic.
But it isn’t.
It’s science!
There’s just a magnetic force pulling them together.
One magnet can reach out over space and pull or push on another magnet.
But, what if I told you, magnetic force does not exist?
You might react with Skepticism.
No no no. No.
or Anger:
That’s it! You’ve crossed a line!
or Confusion:
Huh?
or maybe even Sheer Madness.
Ahh!!!
Come to think of it, that’s a brilliant name for a hair salon.
Haircut Clone! You should call it Shear Madness!
That’s brilliant!
But if you’re a little curious, you might ask:
How do we know what’s real and what isn’t?
We’ve seen this issue before with Centrifugal Force, Coriolis Force, and recently gravity.
None of those forces exist either.
A force is only real if it exists from every point of view.
If it only exists from some points of view, it’s a fictitious force.
So all we need to prove a force is fictitious is to find one point of view where it doesn’t exist.
Let’s take a look at magnetism.
These magnets work because each of its iron atoms
has 4 unpaired electrons whose spins line up each other.
One iron atom affects the others around it forming magnetic domains.
As long as those domains aren’t random, you’ve got yourself a magnet.
Electric current in wires can also exert magnetic force
because magnetism is created whenever charges move.
And, in that lies the problem.
Magnetic force depends on motion and motion is relative.
An electric current is just a bunch of electrons in a wire moving from one positive nucleus the next.
This wire can’t exert any electric forces because it’s neutral.
There is no electric field.
However, the moving electrons do create a magnetic field,
so they can exert magnetic force on other moving charges,
like this proton keeping pace with them.
Well, I mean, it could be anything positive:
A squirrel, a hockey puck, Milton, a rubber ducky.
But, for simplicity, we’ll stick with the proton.
It experiences a force away from the wire.
No problems yet, but let’s change the point of view.
What if you’re moving along with the proton?
It won’t appear to be moving at all and neither will the electrons,
but, now the nuclei are moving the other direction.
Yes, they’re creating a magnetic field, but they can’t exert a magnetic force on the proton
because it isn’t moving.
It’s confirmed!
Magnetic force does not exist.
Yet, that proton still moves away, so what gives?
It turns out we can’t make sense of this without considering special relativity,
particularly, length contraction.
The faster things go, the shorter they are.
Usually, this isn’t something we have to worry about unless we’re going
Fast! Fast!
But sometimes it’s necessary even at slow speeds.
If those nuclei are moving, they must contract along the direction of motion.
But charge is invariant, meaning everyone measures it the same,
so the contraction changes their charge density,
meaning any spot in the wire has more positive charge than negative.
The wire is no longer neutral, so electric force pushes away the proton.
But wait, that electric force didn’t exist from the other point of view!
It doesn’t exist either!
Ahh!!!!
The thing is though, no matter how we look at that wire scenario,
there is always an electric force, a magnetic
force, or some combination of the two.
They’re really just two manifestations of
the same thing.
We call that electromagnetic force,
but representing it mathematically requires tensors, which can be a bit tricky.
So we usually just pretend like they’re separate things.
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and until next time, remember, it’s OK to be a little crazy.
