[HN Gopher] But good sir, what is electricity?
___________________________________________________________________
But good sir, what is electricity?
Author : rapawel
Score : 251 points
Date : 2025-02-23 11:03 UTC (11 hours ago)
(HTM) web link (lcamtuf.substack.com)
(TXT) w3m dump (lcamtuf.substack.com)
| ok_dad wrote:
| My favorite thing about electrical theory is that all this
| business about flow of energy going from + to - is the idea of
| "electron holes" flowing, instead of the actual electrons!
| Basically all of electronics and electricity uses hole flow
| convention. It seems weird to me we don't use electron-flow
| convention (aka: reality), but then again I'm a weird guy.
| snailmailstare wrote:
| I had a similarly funny discussion with a proper engineering
| student on refrigeration insulation and why it isn't more
| natural to express it similarly with temporarily trapping cold
| given the inevitable nature of heat/entropy.
| criddell wrote:
| I remember when I was very young I asked my dad if a
| refrigerator works by moving cold into the box or heat out of
| the box and he told me it was the latter. It's a strong
| memory because he also said something to the effect of that
| being a good question and at that age, comments like that had
| an impact on me.
| jeffwass wrote:
| But that's because of historical precedent, if you weren't
| aware of this then congrats for being one of today's lucky
| 10,000!
|
| Ben Franklin arbitrarily picked the positive anode as the
| starting point when coming up with the idea of electricity
| flowing, long before we had any understanding of atomic theory.
|
| It wouldn't make sense to just invert everything after we
| discovered that electrons are the actual fundamental charge
| carriers.
| ysofunny wrote:
| It seems to me like it's an artifact of how it was all
| discovered and initially implemented.
|
| like scientists didn't realize electrons were flowing in the
| opposite direction, but engineers already had working
| electrical devices
| at_a_remove wrote:
| I have expressed this repeatedly: the assignation of a negative
| value to the electron and a positive value to the proton has
| probably slowed humanity by a decade.
| dotancohen wrote:
| Anybody who needs to know this detail to design or repair a
| device, already knows it. There are no simple enough devices
| where this is relevant for casual repair or modification. You
| can fix your DC devices such as cellphones and your AC
| appliances such as refrigerators, and even design your own
| phones and refrigerators, without knowing in which direction
| the fundamental particles flow.
| srean wrote:
| Could you give one example
| thowawatp302 wrote:
| It didn't
| card_zero wrote:
| The terms are due to Ben Franklin:
|
| _We say B is electrised positively; A negatively: or rather B
| is electrised plus and A minus ... These terms we may use until
| your philosophers give us better._
|
| Here A and B are Franklin's buddies, standing on insulating
| plates while one of them rubs a glass tube with a piece of, if
| I remember rightly (can't find the proper source), "buckskin".
| Then they reach out to join hands and a spark crosses the gap.
|
| Problem is, it isn't even clear from the experiment which of A
| and B really _was_ negatively charged, because it turns out the
| charge depends on the nature of the "buckskin" (or whatever
| term he used), and how hairy, furry, or possibly even leathery
| it was. The resulting charge could be positive or negative,
| depending. So he defined the terms, but _didn 't_ even clearly
| assign them to direction of electron flow.
|
| Edit: the ambiguity is shown in this picture:
|
| https://en.wikipedia.org/wiki/Triboelectric_effect#/media/Fi...
|
| Here leather is above glass, and fur is below it. He was
| definitely rubbing glass with something like leather or fur,
| but the resulting charge depends on where in the series that
| thing was relative to glass.
| saghm wrote:
| As usual, xkcd has a relevant comic about this:
| https://xkcd.com/567/
| card_zero wrote:
| Found it from the horse's mouth, finally: "We rub our tubes
| with buckskin".
|
| https://archive.org/details/experimentsobser00fran_0/page/1
| 7...
|
| Don't know where Randall get "silk" from.
| ThrowawayTestr wrote:
| Silk is usually used in school demonstrations in place of
| buckskin.
| 3eb7988a1663 wrote:
| This makes the robot apocalypse happen at an increased
| rate. All the advancements made without this stupid error
| infecting everything.
| do_not_redeem wrote:
| > We say B is electrised positively; A negatively: or rather
| B is electrised plus and A minus ... These terms we may use
| until your philosophers give us better.
|
| I can relate. This is just a quick hack to get to production,
| we can always rewrite it later!
| fellerts wrote:
| Funnily enough, we still don't fully understand the mechanism
| by which static electricity is built up when rubbing things
| together. Professor Merrifield covers this in a very
| approachable way here: https://youtu.be/0UZb07imNLU. Skip to
| around 6:00 (or watch the whole thing, it's well worth it)
| robocat wrote:
| > but the resulting charge depends on where in the series
| that thing was relative to glass
|
| You'd think we would understand the science of
| contact/static/tribo electricity by now... And yet this
| posted 1 day ago: "Static electricity depends on materials'
| contact history" https://phys.org/news/2025-02-static-
| electricity-materials-c... Historically,
| several studies have suggested that insulators could be
| ordered based on the sign of charge they exchange, from the
| most positive to the most negative. For instance, if glass
| charges positively to ceramic and ceramic does the same to
| wood, then glass (usually) charges positively to wood. Thus,
| glass, ceramic, and wood would form a so-called
| "triboelectric series." The problem with these
| triboelectric series, according to Waitukaitis, is that
| different researchers get different orderings, and sometimes
| even the same researcher does not get the same order twice
| when they redo their own experiment.
|
| Discuss: https://news.ycombinator.com/item?id=43134657
|
| And https://en.wikipedia.org/wiki/Triboelectric_effect#Explan
| ati... There are many cases where there are
| triangles: material A is positive when rubbed against B, B is
| positive when rubbed against C, and C is positive when rubbed
| against A, an issue mentioned by Shaw in 1914.[29] This
| cannot be explained by a linear series; cyclic series are
| inconsistent with the empirical triboelectric series.[75]
| Furthermore, there are many cases where charging occurs with
| contacts between two pieces of the same material.[76][77][47]
| card_zero wrote:
| Woah. Well that just adds to my confusion!
| ok_dad wrote:
| I just came in here thinking hole flow was weird but wow,
| I need to learn some things!
| Sharlin wrote:
| We don't even really understand the "tribo-" part alone.
| Never mind with electricity added.
| genewitch wrote:
| I guessed it meant "rubbing to create electricity" like a
| van De Graaf.
|
| Uh, "tribbing" is a sexual act that women can do.
|
| that's how i figured it out, but:
|
| > 1965, "study of friction," from tribo-, a word-forming
| element in physics with the sense "friction," from Greek
| tribos "rubbing," from tribein "to rub, rub down, wear
| away" (from PIE root *tere- (1) "to rub, turn") + -logy.
| Related: Tribologist; tribological.
| praptak wrote:
| I remember reading an early book on the topic where the
| author describes two kinds of electricity: "glass-
| electricity" and "resin-electricity". The experiments seemed
| to involve rubbing either glass or hardened resin (amber?)
| with _something_. The author (it wasn 't Franklin) concluded,
| after a series of experiments, that this produces two
| different "kinds" of electricity which seem to cancel each
| other out.
|
| Edit: I think I found the author: https://en.wikipedia.org/wi
| ki/Charles_Fran%C3%A7ois_de_Ciste...
|
| His wikipedia page seems to confirm he discovered there are
| two kinds of electricity and named them "vitreous" and
| "resinous".
| db48x wrote:
| And then once you realize that the ancient Greek name for
| amber was "elektron" or "electron"...
| kqr wrote:
| > about flow of energy going from + to - is the idea of
| "electron holes" flowing
|
| You mean flow of charge.
|
| My favourite thing about electricity is how the actual _energy_
| is transferred on the _outside_ of the wires, in _both_ the
| directions of positive and negative charge. Resistance is the
| portion of the energy that accidentally enters the wire. The
| energy flux inside the wires -- and on the surface of the wires
| -- is zero. Just outside their surface it is very high.
|
| A capacitor wouldn't work if the energy came from its poles.
| No, the energy used to charge it enters from the side. This is
| so counter-intuitive!
| benterix wrote:
| > accidentally
|
| Well, we may see it this way, but there's nothing accidental
| in it, it's juts an inherent property of every conductor
| (except superconductors).
| marcosdumay wrote:
| Charge flows on the same medium as energy. There's current on
| the equation of electrical power for a reason.
|
| That bullshit model about electricity flowing around the
| wires is good for generating Youtube engagement, but it
| doesn't represent the actual physics, makes things impossible
| to calculate, doesn't lead to any intuitive understanding,
| and makes things impossible to learn. Or, in other words, the
| model is bullshit.
|
| DC current flows entirely in the wires (up to at least "parts
| per billion" precision), as does energy, because energy flows
| at the same place current flows. AC current leaks. Everybody
| knows that, how it leaks is well known, and there are plenty
| of resources to calculate almost everything around it.
| jmb99 wrote:
| Exactly. If energy flowed around the wires and resistance
| was "the portion of the energy that accidentally entered
| the wire" then larger wires would have larger resistance
| (due to a higher chance of "stray energy entering the
| wire") than smaller wires, which is clearly incorrect. It
| really is a terrible model in almost every way.
| choxi wrote:
| It's weird in semiconductor physics too because the electrons
| flow uphill through voltage potentials
| Xcelerate wrote:
| > Most simply, it [electron] just exists as a particular
| distribution of an electrostatic field in space.
|
| Best simple description of an electron I think I've heard yet. I
| wish we would drop all the dumb analogies. From a kid's
| perspective (at least what I can recall from high school), these
| macroscopic analogies mislead you into thinking the laws of
| physics work differently than what humanity's best models of
| physics actually predict.
|
| For instance, I never liked the sense of "arbitrariness" I felt
| while learning about the periodic table in K-12 school. The
| diagonal rule. Hund's rule. The exception to Hund's rule. And so
| on. Don't even get me started on organic chemistry. But if
| someone had told me "Forget about billiard balls and
| wave/particle duality. Our best models consists of solutions to
| simple and beautiful equations that are extremely difficult to
| solve", then that would have made a lot more sense to me.
|
| The author of the article describes the truth as "weird math". I
| don't think that's necessarily the case. Unitarity is aesthetic--
| it just "feels right". The correspondence of atomic orbitals to
| irreducible representations of symmetry groups is beautiful. Why
| don't we teach that to kids? You don't have to go into the
| mathematical details of group theory, but just let them know
| these odd shapes originate from symmetry constraints. Much better
| than my reaction to seeing an illustration of a d_z^2 orbital in
| high school. I remember thinking "What the heck is that? This
| subject makes no sense."
| aeonik wrote:
| I agree that we should teach the quantum basis of things
| earlier. I just think a lot of people don't know it, and we
| don't have a good curriculum for kids to start with.
|
| We'd also need to revamp some of the math, chemistry, and
| physics curricula to build on the quantum basis of things.
| fc417fc802 wrote:
| > I wish we would drop all the dumb analogies.
|
| They're incredibly useful tools for thinking about things. You
| don't need or want QM to perform most reasoning tasks. Even MO
| is often overkill.
|
| I agree though that we should lead with the truth - that these
| models you're being taught are useful abstractions but
| ultimately wrong. That each successive model brings with it
| more accuracy and nuance but is more difficult to comprehend.
|
| A particular strength of that approach is that after making it
| to QM at the end it leaves you wondering what's next. It really
| drives home the point that the map is not the territory and
| that all we as humans can ever actually have is a succession of
| maps.
|
| > Forget about billiard balls and wave/particle duality.
|
| Actually that one is rather important. QM wave functions really
| do collapse. Things really do switch from behaving like a wave
| to behaving like a particle. This fact has significant effects
| on behavior.
|
| > these odd shapes originate from symmetry constraints
|
| Well they might fit those constraints, but can they really be
| said to originate from them? Is there actual cause and effect
| there? The answer to that would require understanding what gave
| rise to the phenomenon to begin with.
| srean wrote:
| When I was taught the planetary model of atoms I was quite
| suspicious. My reaction was - you can't be serious ... to ...
| are you making fun of me ... to... just because you have a
| hammer ...
|
| Few years later orbitals were introduced as, essentially,
| motion blurs formed by our little zippy guy. I approached our
| teacher and asked what if that 'motion blur' is all there is
| and that billiards ball electron is just a bed-time story.
| That's an adequate way to think he said. Electron mass gets
| more difficult to explain to school kids in this line of
| thinking.
| spacedcowboy wrote:
| All of education is "lies to children". Those lies start off as
| brazen untruths, designed to get the basic concepts across, and
| then we, iteratively, make things more and more accurate as
| time goes by. Eventually, if you go far enough in a particular
| discipline, you'll reach the boundary of our knowledge, and
| that's when things start to get "fun".
|
| I did a physics PhD. I still never got a really good answer to
| a question I asked in year-1 senior-school (11 years old, for
| non-Brits)... "What, exactly, _is_ a positive charge ?" The
| waviness of the hands diminished over time, but it never really
| went away.
| eszed wrote:
| The lie I was told: "it has more electrons than it can stably
| accommodate, so it will give some up to anything around that
| can accommodate moredeg".
|
| What's the next level where that breaks down?
|
| degThough the Benjamin-Franklin-reversed-the-signs thing I
| learned about for the first time up-thread has me thoroughly
| confused. Positive charge means it... Has fewer?
| Workaccount2 wrote:
| There is an old story I read years ago that went something
| like:
|
| When you are in grade school science you are told that a car
| can just be modeled as a cube.
|
| In high school you learn you can use 3 cubes.
|
| In college you learn you can do with hundreds of cubes.
|
| In post-doc you learn to do it billions of points with
| fractal levels of interaction.
|
| When writing the text book for grade school after years in
| physics academia, you write:
|
| "A car can be sufficiently modeled as a cube".
| FilosofumRex wrote:
| Like all simple description it's wrong. It [electron] is a
| quanta of the electron field which is a fermion matter (spin
| 1/2, therefore is charged) subject to the Pauli Exclusion
| principle.
|
| Electromagnetism is one of the four fundamental forces mediated
| by photons which are its basic quanta and is Bosonic field
| (spin 1) and therefore are neutral.
|
| The interaction of these two fields is depicted via Feynman
| diagrams.
|
| Macroscopically observed Electrostatic field of a charged
| capacitor, is mediated by the superposition of virtual zero
| frequency (n = 0) photons, which are off-shell and non-
| radiative. Field's energy arises from the cumulative effect of
| infinite virtual photon exchanges. Whether virtual photons are
| "real" is debatable and confuses those who prefer intuition to
| computation.
|
| https://en.wikipedia.org/wiki/Virtual_particle
| _factor wrote:
| I've always wondered if the electrons bound to a nucleus are
| somehow bound to the element they were attached to.
|
| Changing an element from Hydrogen to Helium or any other variant
| of conversion seems like it breaks an especially solid
| confluence. Each proton determines the atomic number, and there
| is a corresponding electron for each proton after all.
|
| They may float around the universe, but could they still "belong"
| to the element they were formed with, bound to be impacted in
| some way when that element converts to another (in a stellar
| reactor for example).
|
| This would mean electrons are somehow unique most likely, but
| stranger things have been observed.
| aeonik wrote:
| I'm not sure exactly what your imagining, but there are two
| principles that are related to your idea.
|
| 1. Particles are indistinguishable from each other. It's a very
| deep principle, i.e. a lot of stuff relies on this being true.
|
| 2. States and particles can absolutely be entangled ("bound")
| to each other, but it tends to be pretty fragile.
|
| https://en.wikipedia.org/wiki/Indistinguishable_particles
|
| https://en.wikipedia.org/wiki/Quantum_entanglement
| fc417fc802 wrote:
| To be fair, what he proposed isn't (immediately obviously)
| mutually exclusive with your points. If it were true it would
| be almost impossible to detect experimentally.
|
| So it gets tossed on the stack with all the other complex-
| and-unfalsifiable theories for which no evidence exists.
|
| It might make for an amusing sci-fi plot though.
| MalbertKerman wrote:
| > To be fair, what he proposed isn't (immediately
| obviously) mutually exclusive with your points. If it were
| true it would be almost impossible to detect
| experimentally.
|
| The obviousness or lack thereof is subjective, but the
| exclusivity is firmly established. The absolute
| indistinguishability of particles is deeply woven into
| quantum mechanics; you don't get a Pauli exclusion
| principle without it, for example. If the particles
| remembered their previous lives, and an electron that used
| to be tied to an iron nucleus weren't completely identical
| to one that used to be stuck to a carbon nucleus, all of
| quantum mechanics as we know it would be impossible.
| fc417fc802 wrote:
| I don't see why? They could be indistinguishable from our
| perspective while mysteriously being affected in some way
| if certain things happened to their "partner". We can
| experimentally set an upper bound on the permissible
| weirdness but I don't think we can eliminate the
| possibility.
|
| Experimentally you'd be attempting to detect inexplicable
| single particle events above some level of rarity. You'd
| have access to only one side of the pair - you can't tell
| which one the other side is even if it's right in front
| of you (and it almost certainly isn't). So there's no
| discernible (to you) trigger for these events you're
| trying to detect. So you'd be trying to correlate
| frequency counts with bulk conditions as averaged across
| more or less the entire universe.
|
| In the same vein as the God of the gaps the phenomenon
| could always be hiding below the noise floor.
| doop wrote:
| Why does this otherwise excellent series always depict electrons
| as red and protons as blue when everybody knows it's the other
| way round?
| immibis wrote:
| I thought everyone knew that neutrons are blue and electrons
| are yellow.
| MathMonkeyMan wrote:
| Electrons are blue and oxygen is red. Don't be ridiculous.
| simpaticoder wrote:
| Great article! I particularly like this paragraph:
|
| _> It's important to note that while the charge equalization
| process is fast, the drift of individual electrons is not. The
| field propagates at close to the speed of light in vacuum (circa
| 300,000 km/s); individual electrons in a copper wire typically
| slither at speeds measured in centimeters per hour or less. A
| crude analogy is the travel of sound waves in air: if you yell at
| someone, they will hear you long before any single air molecule
| makes it from here to there._
|
| So basically electricity flows like a Newton's cradle. But this
| leaves one nagging question: what is the nature of the delay?
| This question also arises when considering the microscopic cause
| of index-of-refraction for light[1]. If you take a simple atom,
| like hydrogen, and shine a light on it of a particular frequency,
| I understand that the electron will jump to a higher energy
| energy level, and then fall back down. But what governs the delay
| between these jumps? And also, how is it that, in general, light
| will continue propagating in the same direction? That is, there
| seems to be some state-erasure or else the electron would have to
| "remember" more details about the photon that excited it. (And
| who knows? Maybe the electron does "remember" the incident photon
| through some sort of distortion of the quantum field which
| governs the electron's motion.) The same question applies to
| electron flow - what are the parameters that determine the speed
| of electricity in a conductor, and how does it work?
|
| 1. 3blue1brown recently did a great video describing how light
| "slowing down" can be explained by imagining that each layer of
| the material introduces its own phase shift to incoming light.
| Apparently this is an argument Feynman used in his Lectures. But
| Grant didn't explain the nature of the phase shift!
| https://www.youtube.com/watch?v=KTzGBJPuJwM
| marcosdumay wrote:
| > But what governs the delay between these jumps?
|
| What governs the delay between one ball hitting the cradle and
| the opposite ball going up?
|
| It's the electrical equivalent of the same thing. Specifically,
| electricity is delayed by the material absorbing it
| "elastically" for a short time before emitting it back. This is
| usually modeled as a capacitance and inductance on the medium.
|
| > And also, how is it that, in general, light will continue
| propagating in the same direction?
|
| It actually doesn't. It mostly follows the medium. That's why
| you can bend your wires and they keep working.
|
| But if your question is why it doesn't go "backwards", they go,
| but there's an electrical potential there pushing your
| electrons on the other direction.
| simpaticoder wrote:
| _> It actually doesn't. It mostly follows the medium. That's
| why you can bend your wires and they keep working._
|
| Sorry, its my fault for introducing light into a discussion
| about electric current. In fiber optics I believe they add
| "cladding" to achieve "total internal reflection" that
| somehow keeps the light going - not sure how it stays
| coherent though! And in electronics, I assume that the
| boundary of the conductor with non-conductor (e.g. air)
| provides a similar function. I've heard that conductors
| conduct almost entirely on their surface, another curious
| effect I'd like to undersatnd, and I'd also be curious if any
| applications use hollow tubes to conduct large currents and
| save on weight.
| k__ wrote:
| I got told what electricity is in primary school, in middle
| school, in high school, and in university.
|
| Every time I understood it less.
|
| I even watched some videos where people interviewed physics
| professors, to explain what it really is, and the explanations
| only got more convoluted.
|
| Seemingly not because those people were bad at explaining, but
| because if you want to explain it as correctly as possible, it
| just isn't intuitive at all.
| ekianjo wrote:
| it's confusing because all of the words we use in the field
| make it seem like it's akin to water flowing ( _current_ )
| whereas the physical phenomenon is far beyond the movements of
| individual electrons.
| H8crilA wrote:
| The problem with (or the advantage of) the water flowing
| analogy, or even more broadly the discrete element model, is
| that it explains reality good enough to be used in most
| practical situations. Schematics are ubiquitous, yes they are
| "fake", but they are also usually "correct enough". Kind of
| like the incorrect Bohr's model of electrons orbiting the
| nucleus actually does explain the emission spectra (up to a
| point).
|
| But there is an accessible video that explains electricity
| pretty well. Veritasium - The Big Misconception About
| Electricity: https://www.youtube.com/watch?v=bHIhgxav9LY
|
| There is one commonly used concept that requires
| understanding electricity correctly, and not just as a
| combination of waterhoses and gizmos. It's impedance, and it
| directly corresponds to the "controversial" experiment that
| Veritasium is proposing in his video. Impedance breaks the
| pipe-of-electrons analogy.
| BenjiWiebe wrote:
| Are you sure we can't explain impedance with the water
| analogy?
|
| You would have to start with alternating current water,
| since "DC" water maps to DC, where impedance =resistance.
|
| Once you've got alternating water, you can add inductance
| (inertia) and capacitance (rubber diaphragm tanks) and I
| think it all works out.
|
| It's just that we don't have a good intuition for
| alternating water current so it's not a very useful analogy
| in that case.
| Workaccount2 wrote:
| I have gone down this hole many times before and while it
| is kind of possible (the equations for a capacitor and an
| inductor are basically just a spring and a flywheel), it
| just creates really convoluted images that won't fit well
| (or will be too convoluted) when you try to integrate
| into wider electronics.
| srean wrote:
| It's not a bad analogy if you also consider the pressure
| wave. That travels a whole lot faster than the water
| molecules.
| criddell wrote:
| And at each level the degree of confidence seems to be
| dropping. When you get to the point where the explanation
| includes an electron being made from a changes in a quantum
| field and a quantum field is probability, it starts to feel
| like there's nothing underpinning reality.
| immibis wrote:
| Impostor Syndrome.
| B1FF_PSUVM wrote:
| > it starts to feel like there's nothing underpinning
| reality.
|
| "Lock it up, they're starting to catch on."
|
| ;-)
| kzrdude wrote:
| AlphaPhoenix's measurements, experiments and visualisations
| really help! They show some things that are normally not even
| taught and even electrical engineers will appreciate to see
| this. This video he made about it is very good, and worth
| watching if you wonder about how electricity propagates from
| one end of a conductor to the other.
|
| https://www.youtube.com/watch?v=2AXv49dDQJw
| movpasd wrote:
| A point not mentioned by the article: the electrons in a metal at
| room temperature are already moving very quickly due to their
| thermal energy (at the order of 100km/s) -- much faster than the
| speeds quoted in the article, which is what's called the "drift
| velocity".
|
| This thermal motion is essentially random, and the electrons
| constantly scatter off the nuclei every which way, so it cancels
| out and doesn't create a net current.
|
| So, it's less than the electrons gently move under the influence
| of an electric field, and more that it introduced a slight bias
| in the existing thermal motion.
|
| E: To clarify in case it may have been unclear, this is unrelated
| to the speed of propagation of the electric field, which as the
| article says is the speed of light.
| Nimitz14 wrote:
| This feels like a very nice intuition to have thank you for
| explaining!
| sfn42 wrote:
| Is this related to how some materials become superconductors at
| low temperature? Does the slowing down of this electron flux
| improve the material's ability to conduct electricity or is
| there some other mechanism at play?
| khold_stare wrote:
| Superconductivity is fascinating. I don't know how people
| were able to come up with the explanations. Crudely, the
| reduced temperature means less jiggling of the metal lattice.
| This in turn makes it possible for the nuclei to be pushed
| around by electrons to form essentially sound waves (phonons)
| in the lattice (think of the lattice compressing and
| expanding due to interplay with electrons). At a certain
| temperature and therefore a certain frequency of lattice
| oscillation, electrons pair up to form "Cooper pairs" - they
| move in concert due to the lattice movement. What's crazy is
| that cooper pairs become a sort of pseudoparticle, and their
| quantum behaviour is different to regular electrons. Cooper
| pairs have integer spin (as opposed to half-integer spin), so
| they no longer obey the Pauli exclusion principle and all the
| electrons in the entire material basically form one giant
| condensate that extends through the whole material and can
| all occupy the same lowest energy quantum state.
| jaybrendansmith wrote:
| That is the BEST explanation of superconductivity I have
| ever heard.
| khold_stare wrote:
| Thanks for the kind words! For anyone curious to dive
| deeper into the crazyness that is quantum mechanics I can
| highly recommend a few resources:
|
| - Sean M Carroll's work, in particular his Biggest Ideas
| in the Universe books:
| https://www.preposterousuniverse.com/biggestideas/
|
| - Artur Ekert, basically the father of Quantum
| Cryptography has an amazing course for free on youtube:
| https://www.youtube.com/@ArturEkert . It's a very precise
| and understandable explanation of quantum computing, and
| some of the math that is involved with quantum mechanics.
|
| - If you have hours to spare, watch Richard Behiel's
| videos on Youtube. He's like the 3Blue1Brown of Quantum
| Physics. His latest video on superconductivity and the
| Higgs Field is almost 5 hours long (!!!)
| https://youtu.be/DkH1citHtgs?si=-yQNYDu9TlTpE1A0 . It
| builds on his other videos, so I'd recommend starting at
| the beginning.
| mncharity wrote:
| > all the electrons in the entire material basically form
| one giant condensate
|
| _Very_ not my field, but perhaps that 's "all the _paired_
| electrons "? Brief ai-ing (do we have a verb yet?) suggests
| only some small fraction of conduction electrons form
| pairs, let alone all the rest.
| genewitch wrote:
| "Slop pass"?
| cyberax wrote:
| Another way to put it: Cooper pairs become _bound_ objects.
| And so their energy levels are quantized, and to excite
| them, you need to apply more energy than is available from
| the thermal motion of atoms in a superconductor.
|
| This doesn't happen with unpaired free electrons because
| their energy spectrum is pretty close to continuous.
| movpasd wrote:
| Electrons are actually delocalised in a metal: rather than
| point particles bouncing around the nuclei like a pinball,
| they're more like waves that ripple and diffract around them.
| This means that to good approximation, the electrons pass
| right through each other. Because of this, I don't expect the
| electron motion to affect resistance much.
|
| What definitely affects resistance is the vibration of the
| nuclei lattice, in which thermal energy is also stored. This
| vibration makes the electrons more likely to scatter. This
| means even in a non-superconducting metal, resistivity drops
| as you get colder.
|
| The special thing about superconductors is that there's a
| temperature where the resistivity suddenly drops to zero. (If
| you look up "superconductivity resistance against
| temperature", you'll see some graphs showing what I mean.)
|
| I don't know exactly the details of why this happens, but it
| has something to do with Cooper pairs. Electrons in these
| states are also sensitive to being knocked out and bumped up
| to regular conducting states by thermal noise.
| pkoird wrote:
| Just to clarify, the high speed at which electrons generally
| move around in metal is called "Fermi velocity". Like you said,
| since it's random, on average it cancels out to 0. When
| applying an electric field, the electrons achieve a non-zero
| average velocity which is called the "drift velocity".
| tzs wrote:
| It probably should be noted that the reason the drift velocity
| is so much lower than velocity due to thermal motion is that
| electrons cannot move very far before they collide with an atom
| which changes their direction.
|
| The mean distance they move in a copper wire between collisions
| is about 0.00000004 meters. At 100 km/s it would take 0.4
| picoseconds to travel that distance.
| vlovich123 wrote:
| > electrons cannot move very far before they collide with an
| atom which changes their direction
|
| And yet we know it's mostly just empty space. I'm assuming
| it's more because of the electromagnic force being
| particularly strong at those scales rather than a straight up
| "collision" right?
| bavell wrote:
| Isn't a straight up physical "collision" just a strong
| interaction between the electromagnetic field of multiple
| particles?
| hosteur wrote:
| When does anything really touch?
| Terr_ wrote:
| That reminds me of something interesting about biological
| cells. The molecules in that thick stew might be bouncing
| around at 20-250 miles per hour, depending on their size.
| mr_toad wrote:
| What's really mind blowing is how fast the gluons inside
| the protons inside those molecules are moving.
| sebmellen wrote:
| How fast are those moving?
| cogman10 wrote:
| > which as the article says is the speed of light.
|
| This is pedantic because there's practically no difference. But
| just to be pedantic, it's not the speed of light and I'd argue
| it's not usually even close to the speed of light. In
| communications we are talking about anywhere from 60% to 80%
| the speed of light through most mediums.
| sightbroke wrote:
| Confused. Are you saying that, if we took a light bulb (off)
| and a metal rod (0 charge) beside on another.
|
| Then were somehow able to turn the light bulb on and apply a
| charge to the that rod at the same time. While also having a
| detector that can sense a photon and a change in electric
| field some equal distance away from the bulb and rod.
|
| Then the photon (from the bulb) would reach our detector
| before the detection of the change in electric field (from
| the rod)?
|
| Let's suppose the medium is just plain air, and not
| particularly humid.
| Spivak wrote:
| Yes, you can see one of the best people do a demonstration
| of it https://m.youtube.com/watch?v=2Vrhk5OjBP8
|
| It's close enough to c that you should just use c but it
| can be observed that it's less.
| sightbroke wrote:
| https://en.wikipedia.org/wiki/Electromagnetic_radiation
|
| "In a vacuum, electromagnetic waves travel at the speed
| of light, commonly denoted c."
|
| I would expect that in air, that the photon from the
| light source and the perturbance of the electric field
| from the charge to reach the detector at the same time.
| mr_toad wrote:
| Yes, essentially.
|
| The perturbation of the electrical field causes EM
| radiation (radio), which moves at the speed of light.
| B1FF_PSUVM wrote:
| Correct, you're detecting electromagnetic fields in the
| same medium.
| panxyh wrote:
| Yes. What's confusing there?
| sightbroke wrote:
| u/cogman10 comment reads to me as if they are saying that
| EM radiation and light travel at different speeds.
| Tuna-Fish wrote:
| They travel at the same speed, _in the same medium_. c is
| the speed of light in a vacuum, all EM radiation travels
| slower in any other medium.
|
| The complicating factor here is that when you have
| electricity flowing in a wire, the fields are generally
| mostly _outside the conductor, not in it_. That is, the
| signal propagation delay depends more in what you are
| using as an insulator around wire than the material of
| the wire. This has had practical consequences in the
| past; if you replace the insulating jacket of one wire in
| a twisted pair with a slightly different material, on
| long runs it will ruin your signal.
| mr_toad wrote:
| EM radiation, whether radio or visible light is photons,
| and photons only have one speed. However, electrical
| conduction is the movement of electrons, not photons.
| j5155 wrote:
| Yes. As a more common example, fiber optic cabling is known
| to transmit information significantly faster then copper.
| sightbroke wrote:
| I am sorry if my experimental setup was not clear.
|
| Copper is clearly a different medium than fiber optic.
|
| That is why I stipulated a single medium for the
| experiment.
| chongli wrote:
| The speed of fibre optic cabling has more to do with
| signal integrity and bandwidth than any difference in
| propagation delay. In fact, in some cases a signal can
| travel faster on a copper wire (0.8c) than it can through
| an optical fibre (0.6c).
| burnerthrow008 wrote:
| To be even more pedantic, it is 60-80% of the speed of light
| _through vacuum_. Because the speed of light in those media
| is 60-80% of the speed of light in vacuum.
| immibis wrote:
| To be even less pedantic, it's _really fast and basically
| instant_.
| lenkite wrote:
| Btw, Grok explained the point you brought up rather well. I am
| personally finding AI to be better at explaining concepts than
| writing code with imaginary API calls.
|
| "Random Motion: Even without current, electrons are jiggling
| around at high speeds (~106 m/s at room temperature) due to
| thermal energy. The electric field just adds a slight bias to
| this chaotic motion, resulting in the net drift."
| whatshisface wrote:
| The difference is that if you ask it to write code, you'll
| find its mistakes, but if you ask it to explain neutron
| stars, you won't.
| iandanforth wrote:
| For introductory articles like this I also find it helpful to
| know that the whole positive / negative thing is arbitrary. In
| fact the assignment of "negative" to electrons arise due to a
| mistaken interpretation by Benjamin Franklin of one of his
| experiments. So if you're wondering why gaining the primary
| mobile charge carrier makes things more negative blame Ben
| Franklin!
| FabHK wrote:
| I wouldn't call it "mistaken". It was an arbitrary choice at
| the time, nothing but a naming convention.
| mackman wrote:
| As someone who studied physics and electronics for many years, I
| still appreciate an article like this for reminding me how
| profoundly weird science is. Working day to day with the
| equations and practical applications of electricity gives you a
| false sense of confidence that we actually have any fucking clue
| what's going on.
| ffsm8 wrote:
| *how profoundly weird _reality_ is. (*_ *)
|
| Or is it " _how profoundly weird this simulation is_ "? we'll
| never know!
| djsamseng wrote:
| There's also the field theory of electricity:
| https://youtube.com/watch?v=bHIhgxav9LY
|
| It's an eye opening alternative explanation to the electrons
| flowing like a chain theory of this article.
| jvanderbot wrote:
| > Pay no mind: it's enough to say that most nuclei on Earth were
| formed through nuclear fusion in stars and won't undergo any
| change on the timescales of interest to electronics -- or to
| terrestrial life.
|
| It's impossible for me to understate how awesome this is. And how
| hard it is for me to truly grok.
| frutiger wrote:
| Yes, and in particular that it's in all the "ordinary stuff"
| around you - wood, air, glass, sand. Reality is truly
| extraordinary upon any closer examination.
| karaterobot wrote:
| This was pretty clear and readable, I guess. But the most
| succinct explanation of electricity that I know of is from
| Stephen Leacock:
|
| > Electricity is of two kinds, positive and negative. The
| difference is, I presume, that one comes a little more expensive,
| but is more durable; the other is a cheaper thing, but the moths
| get into it.
|
| And that's sort of all I need to know.
| jimbob45 wrote:
| _In pop-science articles and videos, the concept is usually
| illustrated using the dated but intuitive model developed by
| Niels Bohr around 1918. The model envisions electrons that travel
| around the nucleus in circular orbits:_
|
| Please stop teaching the history of what we _used_ to think the
| atom looked like. We've reached the point where we spend 99% of
| the material teaching what we know the atom _doesn't_ look like
| and very little on what it does look like. Even this author
| offers a picture for what it doesn't look like and nothing for
| what it does. Physicists should know the value of a good picture
| /mental model better than anyone else.
|
| I challenge you to go on Wikipedia and find the article/space for
| the current understanding of the atom. Was that hard for you to
| find? Would a curious high schooler have enough information
| within that article/space to learn everything you now know
| (textbooks are too expensive and inaccessible for high schoolers
| to rely on, physics websites are hit/miss). Is this how you would
| prefer to have been taught?
| oh_my_goodness wrote:
| The picture of electrons sitting in states (or the empty states
| without electrons) is not used for historical reasons. It's
| used because the next level of explanation requires partial
| differential equations.
| erehweb wrote:
| There is a story of a student taking an oral exam at Oxford or
| Cambridge many many years ago.
|
| Examiner: "What is electricity?"
|
| Student: "Oh, I do know, I mean I used to know, but now I've
| forgotten."
|
| Examiner: "How very unfortunate. In the whole of history only two
| people have known what electricity is - the Creator and yourself.
| And now one of the two has forgotten."
| dmos62 wrote:
| I've heard it said that we don't know what electricity is or
| how it works. To what extent or in what sense is that true?
| CamperBob2 wrote:
| That goes along with the other old saying, "All models are
| false, but some models are useful." We don't know what
| electricity is in the sense that if you keep asking "But why
| does object X cause (or experience) effect Y?", you will
| eventually reach a point where we don't know the answer.
|
| In that sense, we don't know what _anything_ is. But we can
| still use it. And because everything we learn seems to become
| useful sooner or later, it doesn 't pay to stop asking.
| JALTU wrote:
| I'm not sure that was the point of the poster's question
| about electricity, because I've heard the same assertion
| made by science writers and such.
|
| Our current BFF, ChatGPT, says the question is about
| "charge" in that we don't know why particles have a charge.
| So what is a "charge" and why? Gravity is also presented as
| a thing we don't fundamentally (ontologically) know about.
| Interesting!
|
| And not disagreeing with the desire to keep asking, nor
| with the desire to find a final answer. The author of the
| article puts it fairly well:
|
| We don't have philosophically satisfying insights into the
| universe at subatomic scales...there's no straightforward
| explanation of what a bound electron actually does: it's
| not orbiting the nucleus or spinning around its own axis in
| any conventional sense. Most simply, it just exists as a
| particular distribution of an electrostatic field in space.
| immibis wrote:
| The answer to "why?" has to stop _somewhere_.
| vasco wrote:
| Why?
| MrMcCall wrote:
| Because 'unknowable' will stop you cold.
|
| And many unknowns are practically unanswerable.
|
| But don't worry, you won't exhaust the findable.
| tim333 wrote:
| It depends how deep you go. I mean it's the force between
| charged particles and their movements but if you go too deep
| into how did the laws of physics get there and what are
| electrons made of you get stuck.
| benterix wrote:
| > The field propagates at close to the speed of light in vacuum
| (circa 300,000 km/s); individual electrons in a copper wire
| typically slither at speeds measured in centimeters per hour or
| less.
|
| It would be worth mentioning _why_ it happens as it 's quite
| interesting.
| AlienRobot wrote:
| I'm no physicist, but if I remember correctly, light is some
| form of electromagnetic radiation, which means EMR travels at
| speed of light. In that case, it's not surprising that an
| electrostatic field can travel at similar speed.
|
| From my understanding the quote is talking about electrostatic
| effects that occur when electrons move to fill a void/go away
| from a negatively charged area. Since the force that makes
| electrons repeal each other is very weak, I think it makes
| sense. But note that it mention "a single electron." Voltage
| deals with a difference in immense scales of electrons, so I
| assume the effect and speed would be different in practical
| cases.
| alabastervlog wrote:
| On a whim, I bought a book called _There Are No Electrons_ at a
| used book store, some years ago.
|
| The idea of the book is that we spend lots of time teaching
| students various incorrect and inconsistent models for how
| electricity works, that also don't optimally build intuition for
| _working with_ the stuff.
|
| The book's remedy is to say "forget all that: here's a wrong
| model that _is_ good at building intuition for working with
| electricity, and if you're not planning to go for a physics PhD,
| that's much better for you than the other wrong models"
|
| I don't know enough about electricity to evaluate whether this
| was a good idea or well executed, but it's an interesting
| approach.
|
| https://goodreads.com/book/show/304551.There_Are_No_Electron...
| xandrius wrote:
| Could you give a gist of such a wrong model?
| holoduke wrote:
| The classical model of an atom with circulating dots
| representing electrons. I believe those dots must be more
| like waves.
| tigerlily wrote:
| Or the plum pudding thing. Oh, and phlogiston.
| genewitch wrote:
| If that's the book I am thinking of everything an analogy
| with little aliens called greenies that bounce on
| trampolines.
|
| I couldn't get through it. I got to just past the holes part.
|
| It is written well, so might be worth a shot.
| therealdrag0 wrote:
| "There is no X" is an interesting trope. I've heard it with
| Fish and Trees as well.
| nayuki wrote:
| > what is electricity?
|
| My favorite answers are:
|
| * http://amasci.com/miscon/whatis.html
|
| * https://blog.rootsofprogress.org/the-significance-of-electri...
| danso wrote:
| Ever since seeing this time traveling meme [0], I'm constantly
| thinking about how I would be the worst time traveler ever. Maybe
| I could explain flight? But not electricity, definitely not the
| engineering needed to make it usable.
|
| [0] https://cheezburger.com/9253930240/this-electricity-
| business...
| thetwentyone wrote:
| > A crude analogy is the travel of sound waves in air: if you
| yell at someone, they will hear you long before any single air
| molecule makes it from here to there.
|
| Isn't this a very good analogy? What's so crude about it?
| anthk wrote:
| I used to read W. Beaty, the guy from http://amasci.com/
|
| Still, getting electricity right is not easy.
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