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Comment by jagrsw | Hacker News Reader

The video is interesting, but I suspect, that the author is making some subtle errors at places. Tho I'm not 100% sure, last time I analyzed those subject was at BsC/MsC courses at my uni.

E.g. he says something to the tune of

   electrons take a few ns. running around, and then settle down in the maze.

IIRC electron flow in a medium is relatively slow, something on the order of centimeters per second. So it's not electrons which settle some potentials by moving quickly, but the electric potential finds its equilibrium. And it finds its equlibrium by electrons exchanging virtual photons (carries of electromagnetic force)?

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The author has a fascinating video (part of a wider effort of many science YouTubers) that tries to clarify all that.

https://www.youtube.com/watch?v=2Vrhk5OjBP8

I’m actually not sure if that makes his explanation more accurate because it’s informed by that, or more regrettably forced metaphor. But the whole series of videos from different creators is worth watching if you want to understand the whole “electrons are moving” thing.

Here's a good Physics SE answer that addresses this point. The "electrons move slowly in a wire" is a hypercorrection, similar to "light slows down is glass": https://physics.stackexchange.com/a/13568.

Parent didn't say electrons move slowly. Parent said electron flow is slow which is true. The article tries to say that in that average there are fast-moving parts and slow-moving parts. Fine.

No, that's the wrong interpretation. The truth is that there is no such thing as "electron flow". It's not a quantum mechanical concept, just a classical approximation.

I feel that one of the differences is that a wire is "full" of electrons already, and more are reluctant to enter the wire unless there is an exit path, but as soon as there is a path the current/charge/emf flow occurs all along the wire almost simultaneously.

This is not modelled well with the water mazes/analogy.

In what way is it not?

The movement of water molecules is typically much slower than the wave speed of water.

When you turn on flow to a filled pipe, the water is reluctant to enter the pipe faster than other water is leaving the opposite end (mediated by pressure waves).

Mainly because the maze is empty to start with, and the water must flow simultaneously to all points equidistant from the entry until the exit is "found".

The analogy would work better if the maze would start with entrance and exit closed, and filled with water to half height. IIRC the author mentioned this in a comment under the video.

At one point in the video, he appears to splash clear water into the filled maze. You can see the non-moving parts lighten their colour compared to the active path.

It can be modelled, but with a slight twist. If in a water analogy we prefill the maze with a water and then connect it to a source and a drain, then water level will raise near the source and fall near the drain. We'll see then how it propagates through the maze, these waves will meet somewhere, then some more hard to describe action will follow and then the system will settle to a dynamic equilibrium.

This way the water level changes probably can propagate faster then water moves. Though probably to get this result we'll need to make a "deeper" maze. I mean make walls higher so a cross section of a path would have bigger area, so a slow flow multiplied by this area would give us a big volume of a water moving. Big enough to raise level of a water fast in a whole section of the maze.

the drift speed of electrons in a conductor is, as you say, low, while the fluctuations of the wave travel at near the speed of light, and electrons can be accelerated to near light-speed but I don't think that happens in normal signal transfers.

Even if the electrons move slowly, it can remain true that it only takes a few ns for them to settle down. The time for any of the "wrong paths" to have their current drop to zero after the switch is thrown will be determined by the RC time constant of that path, where C is the stray capacitance and R is the path resistance. That's going to be over pretty quickly.

You are thinking about drift speed of electrons, which is slow. But when the initial voltage is applied, each electron would feel the electromotive force and “jiggle” around a bit which would be nano seconds and then settle.

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