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 brillia
nt 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 p
oint 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 c
an’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 requi
res tensors, which can be a bit tricky. So we usually just pretend like they’re separate things. Thanks for liking and sharing this video and a special thanks to our patrons on Patreon who have been a huge help. Please subscribe if you’d like to see more and until next time, remember, it’s OK to be a little crazy.
Comments
I've remade this video and I've given the topic the time it deserves: https://youtu.be/Ii7rgIQawko (How Special Relativity Fixed Electromagnetism)
Actually there is a barber shop in Austin called Shear Madness.
As a plasma physicist I was ready to rage on here, but as it turns out you're dead on the money - electric and magnetic forces are coupled. Hence what appears to be an electric force in one frame of reference may manifest as a magnetic force in another frame of reference.
Absolutely correct. While special relativity forced us to change much of our views of physics, Maxwell's equations needed no change whatsoever. They were already relativisticly correct. What I tell my students is that magnetism is merely the relativistic correction of the electric force.
This channel takes the difficult and makes it "fun and easy' to understand. Nick is a genius and makes science easier to understand. Don't get me wrong, I only understand a portion of this stuff, but it's a lot more than I get from audiobooks on the same subject. He takes what I thought I knew and presents it in such a way where the loopholes of misunderstanding are plugged up. I'm glad there is so much I don't know, now I have a reason to learn it in a new light. Nick makes it fun. He's funny, entertaining, and an excellent professor. I must assume he has a Phd in physics. Yes? No?
I've been searching for a video like this for a couple years now. You nailed it! Thanks for presenting it in such an accessible format.
Man, you can take any subject on the planet and make it interesting. That's a gift.
Wow, I’m both confused and enlightened simultaneously. My brain hurts but I like it.
I still don't really get magnetism. Everywhere I look for an explanation seems to define magnetism in terms of itself. And why do they say that electric and magnetic waves are perpendicular to each other if they're actually one in the same? I'm sorry for not getting this well, but I have such a hard time visualizing what's responsible for what, and how.
I like your approach to the unification of forces... then defining forces... then defining the entities that define forces (and the forces we are based upon, where we can call something 'alive' or 'evolving' in a defined forward time).
This might be the first channel I support via patreon just because the content is so good and yet the subsciber count seems low.
Great video! Didn't know about special relativity until now but I don't think I am at that level of physics so this is a good reference video for my future physics studies. Keep rolling!
Nice job on explaining about electromagnetism Nick.You deserve more recognition. Keep up the good work:-)
This channel is pure gold.
I never thought of the impact of length contraction on the observation of charge neutrality of a live wire. Interestingly, the length contraction argument applies in the wire rest frame as well. It must be that the electrons in the current naturally space space themselves out in a way that exactly compensates for the length contraction an observer in the wire's rest frame would measure in order to preserve charge neutrality in the wire rest frame. Thus, only in the rest frame of the wire (or in an inertial frame moving perpendicularly to the wire) does the wire appear to be charge neutral. In any other inertial frame, the length contractions of the wire and the electron current would be different. This would result in observations of non-neutral linear charge densities... Cool stuff! Thanks for sharing!
I am really-really in love with the moment, when music started playing. It's been so long, since I heard some motion in science explanations!
Nice job! Enjoyed the "perspective" and genuine truth presented.
"it's okay to be a little crazy" I liked that one
Please, please tell me how this explains the force exerted between two particles with spin
This channel ought to have millions of views!