He explains to the interviewer that it’s related to the same reason you can’t put your hand through the chair. In a magnet, the atoms all line up and that same force gets magnified so that you feel the repulsion from a greater distance.
I already knew that when you touch an object, you’re not actually touching it. It feels solid because of electrical repulsion. So Feynman’s explanation makes sense.
But is there an example in everyday life (like pushing on the chair and it pushes back) to explain the attraction between magnets?
The whole point of that clip is that he’s not explaining magnets. He’s explaining how, when most people say they’re explaining magnets, they’re wrong, and highlights that by pointing out other phenomena we think of ourselves as understanding but which most of us actually don’t. Feynman, unlike most folks, can actually explain magnets, but it takes about a semester, if you already have quantum mechanics and DiffEQ under your belt.
The explanation of the chair is fine. But the “why” is why charges behave this way. And the analogy doesn’t explain repulsion any better than attraction: without doing much deeper into QM, all we can say is that opposite charges attract and like charges repel.
As it happens, solid matter is made from atoms, and atoms have electrons on the outside, which repel–so it’s hard to push the atoms too close together (there are other effects going on [the Pauli exclusion principle], but let’s not get carried away). But the nature of the repelling isn’t explained at all, and so it’s no better an answer than saying that electrons and protons attract each other because they have opposite charge.
It’s not too hard to show that magnetism derives from moving charges, and so (until a monopole is discovered) the only answer you really need is why charged particles behave that way. But to go further down the rabbit hole you need some heavy QM, and you still end up with an unanswerable why.
The chair thing isn’t a great starting point. The repulsion you feel with the chair involves a lot more than you need to get where you’re trying to get.
The shortest path you might take is to recognize that, for electrically charged things, opposite charges attract and like charges repel. You might have some familiarity with the attractive aspect of electricity if you’ve ever seen a piece of static-y plastic stick to your hands or a wall (although already there’s some cheating there since one of the objects involved may be merely polarized). But an attractive aspect of electricity can be exhibited this way all the same. Then if you’re willing to accept that magnetism and electricity are intimately related, it’s not so crazy that both would exhibit attractive and repulsive behavior.
The problem is that it’s a very simplified version of the real explanation; that is, it takes the wavefunction notion seriously, bringing “momentum space” and “position space” as two separate-yet-related entities into the picture immediately, and that simply doesn’t gel with the notion of photons and electrons as little ball bearings flying around bumping into each other. It even says that Feynman diagrams, which laypeople find so appealing and intuitive, are the wrong way to approach this problem, because they’re used to answer different questions.
The end result is a nice little explanation with no equations and plenty of diagrams which doesn’t connect to anything in the popular misunderstanding of quantum mechanics. There’s no simple path of refining the ball bearing model into the wavefunction model because the ball bearing model is fundamentally ill-founded, and this problem shows exactly how it’s fundamentally ill-founded, and what you can’t explain when you start from that foundation.
It reminds me of the water model of electricity: You can explain quite a few things if you think of electricity in wires as being like water flowing through pipes. Voltage is pressure, resistance is how freely the water can flow, and amperage is how much water is flowing past a fixed point every second. Capacitors are like water tanks, resistors are like baffles or other partial blockages, big wires with little resistance are like large-diameter pipes, little wires with more resistance are like narrow pipes. You start from that, and you can explain things like RC circuits and light bulbs and lots of other things, and you think that it’s a good model until you find out what inductance is.
And once again, there’s simply no path from here to there. Flowing water doesn’t have inductance, throwing balls around will never net you an attractive force, and some things can only be visualized in terms of abstract mathematical models.
Great link. Yes, it’s vastly simplified. But it provides a fairly intuitive explanation of the why behind the uncertainty principle and of how both attraction and repulsion naturally arrive from the interaction of the exchanging virtual particles.
What is cute is they way you can use simple electrical system tools like Spice (or more modern easier to use ones) to create a simple electrical circuit that has component values chosen to be the analogue of a mechanical system. Springs and mass; air, boxes, speaker cones (more springs and masses); water, pipes, tanks; etc. Then you use the tool to predict the system’s response to stimuli.
Designing simple speaker enclosures with Spice was a very common trick. Even better, you can add the crossover in the same domain. By modern speaker design standards it is a pretty primitive way to go, and only models the gross parameters, but it does produce a pretty good initial result.
It’s common in nuclear engineering to treat neutron flux as akin to an ideal gas. Which is also an interesting example of an analogy that works better than one might naively expect.
Which brings me to a question for anyone/everyone:
Is it more valid to think of electricity as a liquid composed of electrons (or holes) or as a gas composed of electrons (or holes)? At very first glance electricity seems “incompressible”, so a liquid would be a better model. OTOH, electricity does seem to be “decompressible” which gives it some gas-like attributes.
Maybe, given the high speed of electricity propagation, it might better be modelled as a very, very viscous liquid. One whose “speed of sound” approaches a hefty fraction of c in favorable materials. IOW, like pitch, but massively more so. Which would be the polar opposite of a gas.
Thoughts?
There is an excellent series of pages on-line describing various quantum and particle physics topics for the lay audience, written by Prof. Matt Strassler. Here, for example is his explanation of those mysterious “virtual particles”, which he claims would be much easier to understand if they had never been called “particles” in the first place.
Poke around his site, there’s a lot of good and clearly written (and illustrated) stuff there.
