> Canonically, electric current results from the collective movement of electrons, each carrying one indivisible chunk of electric charge. But the dead steadiness of Chen’s current implied that it wasn’t made of units at all. It was like finding a liquid that somehow lacked individually recognizable molecules
In maxwell's equations, current density J is defined in terms of the E-field. When talking about electricity, people make the typical quantum mechanical wave-particle mistake. Electricity refers to two things, photons and electrons and how they interact with eachother. Both act as wave-particles, but photons act more like waves and electrons more like particles. The thing that gets people is that photons are the things that move energy around. A photon is an electromagnetic wave. In a wire, you can have an electromagnetic wave traversing the wire at some proportion of the speed of light, while the electrons are moving at speeds closer to meters per second. We defined current to be proportional to the E-field (because that is what is moving the energy) and thus we shouldn't refer to the movement of electrons as current.
One of Maxwell's other equations links the E-field to charge density. You can't talk about the time derivative of the E-field without also talking about the time derivative of charge density.
It's true that interactions between charged particles invoke photons, but you can have charged particles (and their associated E-fields) travelling at constant velocity in a vaccum and still define an associated current density without considering photons. I'm not sure your interpretation produces a useful intuition for this situation.
One of the underlying ideas of the paper is that, in conventional metals where conduction band electrons are much more wave than particle, you can still measure when they 'enter' and 'exit' the material through perturbations in the field, that is bursts of photons that occur when electron waves interact with an obstacle.
> you can have an electromagnetic wave traversing the wire at some proportion of the speed of light, while the electrons are moving at speeds closer to meters per second.
This isn't as unintuitive as it sounds though.
In a water pipe you can have a pressure wave reach from one end to the other very quickly, even as the individual water molecules move very slowly.
If water pressure is voltage, water molecules are electrons, and the pipe is the wire, then it's easy to see how a "voltage" can reach the other end of a "wire" without any of the "electrons" having to move very far at all.
The problem with this analogy is that pressure waves can only travel in a medium. The pressure wave exists because the particles in the medium bump against eachother to propagate energy so the analogy gives people the impression that electrons are bumping against eachother to propagate energy. Photons are distinct entities that can travel without a medium. See michelson-morley experiment. Electricity is nothing like what we experience on our macro scale. Analogies never convey the full story.
The analogy does not completely explain the actual behavior of electrical current, that's true. But what's more important, and what it does clearly show, is that a fast wave can exist without fast movement of the particles involved.
> the analogy gives people the impression that electrons are bumping against eachother to propogate energy.
If this is not approximately how electricity works, why does the current stop flowing when you disconnect the wires, or equivalently when you "connect" them via something that doesn't have free electrons (i.e. an insulator)?
TL;DW: the power is transferred by the electric fields, it's the electric fields which move the electrons, if there's a break in the circuit the electrons necessarily accumulate in the places that minimise the electric fields.
Unfortunately the explanation to your question is something that takes years of education to understand and even then, most people just come out understanding some parts. The best I can do on an internet forum is tell you that the analogy is wrong, because experiments told us its wrong. My advice is if you want to understand this stuff, do the math! ;)
This is not even approximately true. j is not “defined in terms of E”. It occurs as a source term in one of the inhomogeneous Maxwell equations, and consistency with the other inhomogeneous one (div D=rho) requires that div j = dot rho, which means that j is the flow of charge density. So, I guess if electron movement shouldn’t be referred to as current, we shouldn’t refer to electrons as charges, either…
When solving for the wave equation, the substitution made for J is sigma * E. So defined in terms of the E field and some conductivity constant. When solving the wave equation, there is no mention of charge density, everything is fields. This predicted the existence of electromagnetic waves. In reality, we know there is only electrons and photons. So thus the wave equation is the source of truth and what we call fields are just a consequence of the complex interactions between electrons and photons and this is studied in quantum electrodynamics.
It is however still movement, which is important because static electric fields don't produce magnetism, whereas moving charges do - which is the principle benefit of AC current.
Well, technically that depends on your reference frame. If the _observer_ starts moving, they will observe a magnetic field where before there was only electric.
It’s not that static electric fields “produce” magnetism. Magnetism is a result of relativity.
Imagine a simple circuit, say a light bulb and a battery. Electrons move from the negative terminal, through the bulb, and back to the battery. The net change in number of electrons at any one point is zero. The energy isn't in the electrons themselves, but in the motion of those electrons. Electrons in must equal erlctrons out.
Even a battery doesn't store electrons. It uses the energy carried by those electrons to reverse a chemical reaction. The energy is stored chemically.
If you think about it, the electrons belong to the physical materials in the circuit. You can't really add or remove electrons* as electron count is a fundamental property of those atoms. If you somehow removed electrons from the system, you'd be changing those atoms and the system would no longer be able to pass current at all.
*you can, of course ionize atoms by adding or removing electrons, but that's not exactly what happens in electric circuits
Electrons are not electricity, they just carry it. Kind of. It's really complicated.
In order to get a sustained current, you need to put electrons in one end and take them out from the other in equal numbers. Thus mass doesn't change.
However, if you're talking about static electricty, you can actually create a mass imbalance by taking a few electrons away from one side or putting some electrons on the other. It's a very, very, very small change in mass.
Whoa, really? Their answer was pretty spot on to your question. Why take such a hostile attitude when it’s your own inability to understand? I’m shocked to see such an ignorant and condescending comment being upvoted.
There’s nothing wrong with not understanding a technical explanation and asking for it to be simplified to your level of understanding, but this is not a simple concept to explain because it is ACTUALLY complex and counterintuitive. How is it their fault?
I'm just trying to answer your question, but I don't think you're exactly clear on what you want to know. It's ok, no need to get defensive about it.
Whether or not 'one end of the wire gets heavier' depends on what your doing. If you are using the wire to power an LED from a battery, then no, because electrons are removed from one end and placed into the other at equal rates. Charge and mass within the wire are both globally and locally conserved.
If you do something where charge/mass isn't conserved such as removing electrons from one side (i.e. by rubbing a fork on a carpet) or by using an electric field to 'tilt' the electrons to one side, you can create a (very small) mass imbalance. This activities are not usually considered to be useful electrical current.
You're talking about conventional current, and it's nothing more than a polite fiction. We model circuits as current moving from positive to negative, but with the implicit understanding that the real charge moves the opposite direction.
Positive charge carriers do not actually exist[0]. There's only electrons and holes they can go into. We can talk about the movement of holes, but that's a virtual charge carrier at best.
Conventional current is just a convention. It's what we started with (because Franklin was wrong) and it's too much effort to change now. In practice, the distinction almost never matters. Sometimes it does, but not enough that it's worth overhauling the entire field of electronics.
[0] of course positrons and protons exist, but they aren't relevant to electronic circuits
Yes, but to an unmeasurably small degree. Electromagnetism is very strong, so you never see the density of electrons change by very much, or the situation will correct itself quite violently.
A difference in voltage between two points in a circuit is a difference in concentration of electrons at those two points, and since electrons have mass that's not quite zero, the location with the higher concentration of electrons will have very slightly higher mass density. But this is true for any electric potential (voltage) difference, whether or not there's any current flowing.
An electron has .05% the mass of a proton, and only a small imbalance of electrons and protons is necessary to generate extremely strong electric fields by earthly standards.
Imagine a loop of pipe filled with water, and a pump pushing the water: The water moves around the pipe. The movement doesn't cause any part of the pipe to get heavier.
Imagine a different scenario, where the pipe ends in a big box: This time the box does fill up with water, and gets heavier.
Mapping the analogy from water back to electrons: a loop of pipe is like a loop of wire and a battery; while the pipe ending with a box becomes a capacitor or antenna, and that will leak[0] before you can measure the mass change — but technically yes the the mass of any given wall of a capacitor or of an antenna will be very slightly changed by this sort of thing.
For a sense of scale, to get a total charge of 1 coulomb using electrons, the mass of those electrons will be about 5.7 nanograms, and trying to squeeze that much charge into the last millimetre of some length of a wire 1mm in cross section diameter, involves about 60% of the energy in this explosion: https://www.youtube.com/watch?v=wqKn_3iJOP4
As nothing gets close to being able to hold that kind of energy, even if you're trying to accumulate a lot of excess electrons, those electrons leak well before even coming close to nanograms of excess mass.
Bruh its simple physics, does one end or the other get lighter, by all measures we care about, not really, the mass of a proton or electron is beyond any consumer hardware measurement. I doubt it would matter beyond extreme scenarios or controlled experiment
The answer is yes but you can't practically observe it. The electrons repel each other so strongly that you can't accumulate enough of them in one place to be able to observe change of mass of that object.
You can move whole charged atoms, that's a form of electricity too, and it can add observable amount of mass, like with electroplating or welding. But these very quickly turn electrically neutral after depositing.
There's a confusion this article isn't helpful with: there are physical electrons, the actual physicalparticles. They move in the metal very slowly. But, their motion propagates very quickly, and turns out that the change in motion acts almost exactly like an electron itself, up to having a different mass. This is the "electron" quasi-particle, which is the abstraction that's breaking down. this only shows up about a screen or two deep into the article.
I thought these concepts are lower division EE undergrad concepts? AC power clearly depends on electron motion and electron drift velocity is one of the first things they teach about electricity. Maybe I'm a dummy and I'm missing something but I don't understand why this is groundbreaking.
He got his doctorate and now he's getting paid, presumably, the big bucks as a research data scientist at Barclays. Not everyone who gets a PhD actually wants to be an academic!
I am sure he would stay in academia too if they gave him tenureship immediately after graduation and paid him as much as a quant (academia does pay decently, but only if you are a senior tenured professor).
I remember one of the first question asked in university was "what's an electric current?" I said something along the lines "it's a directed flow of charged particles". The professor asked do you contain charged particles, do you move, are you an electric current?
Not a huge fan of the top answer and pretty disappointed by it being voted so highly:
>The idea that electricity "does not exist" is just verbal sophistry along the same lines as "matter does not exist, it is frozen energy" or, "you do not exist, you are a figment of your own imagination". At best these are all just over-dramatic and misleading ways of saying that what these things actually are is not what you probably think they are. At worst, misguided eccentrics create "straw" definitions of such well-known words just so they can burn them and trump them with their own untenable notions.
"You do not exist" or "matter does not exist" might be unhelpful sophistry or they might be thought-provoking invitations to a deeper discussion. It depends on the context and the intent.
If this blogger is "basically sound at an experimental and phenomenological level", isn't demanding public denouncements and retractions from everyone using the term "electricity", and has no shortage of thoughts and elaboration about his "eccentric" thoughts on the subject then what exactly is the harm here? Where is this user's uncharitability and hostility coming from?
Drilling into definitions, or "quibbling over semantics" if you prefer, isn't always fun for everybody but that doesn't mean there's an inherent need to come in and break up the party.
I think the top answerer had a few electric bugbears they wanted to get off their chest. Best skipped over, and time spent looking for simple and thoughtful answers. It's a shame the stackoverflow model isn't proving effective for that oft-asked question.
I remember one of my physics professors at uni explaining this theory and for some reason, I had this weird anxiety at the thought. A lonely electron doing all the work of every electron in the universe. Semifun fact, Feynman used the electron traveling back in time analogy to help teach the principles of QED.
The theory also has some merit at least in the boundaries of QED, it's impossible to draw a QED Feynman diagram where the arrows representing positron/electrons just stop, each one must eventually reach the other end of the diagram.
It doesn't quite work as you move beyond that, you get stuff like neutrons decaying into protons and electrons (and some neutrinos somewhere). Unless of course you take seriously consider Wheeler's suggestion that the positrons might be hiding in the protons.
Given that gravity has been observed to work on antimatter the same way as it does on normal matter, doesn't that refute this? or is there another aspect of symmetry that keeps it consistent?
I’ve always wondered if you tried to run a current through a metal belt moving in the opposite direction of electron flow at a speed higher than the drift velocity if the circuit would complete?
(For the sake of argument let’s says it’s not connected like a belt would be. )
This experiment actually gets very feasible if we replace electrons with ions, and the metal carrier with (e.g.) an aqueous electrolyte in an electrochemical circuit. Something like splitting water in H2SO4 would be an easy starting point. This means our charges no longer move at relativistic speeds, and have very short mean free paths, therefore it is possible to flow water[0] against the electrical flow of ions at greater than the mean diffusion speed.
My not overly confident understanding[1] is that this does in fact break the circuit and prevent the flow of current.
Also worth noting, by choosing a colorful ion choice of ion it is possible to directly observe their formation and travel. You can also use electrons as your negative ion directly in liquid ammonia, forming a pretty deep blue solution.
My first impression is that yes, the circuit would complete.
Keep in mind that the metal has both negatively charged electrons which are reasonably free to move around within the metal and positively charged protons that are generally in the nuclei which are fairly fixed within the metal.
If you have the metal belt moving so that the electrons are not actually moving (from the point of view of a stationary observer outside the belt) that observer would see the protons moving.
You've still got, from the outside observer's point of view, a current. It just is now a proton current instead of an electron current.
Isn't current an instantiation of an electro-magnetic field and so the movement of the belt wouldn't matter? It all lights up at the same time. Considering a conveyer belt portion that is part of a circuit, doesn't the portion of the belt that is energized change as fast as the belt moves?
Yes, because the circuit is an alignment of charges that creates a electric field. The fact that electrons drift along it is immaterial to the circuit functioning.
For things to get weird you would need to have the belt moving at relativistic speeds, >80% the speed of light.
It is very material: the movement of charge is necessary for electricity. In this case electrons are still moving into and out of the belt, even if the bulk is not moving in the direction of the flow of current.
Put yourself in the frame of reference of the moving belt. An electric current is running through you, and also some other machinery around you is moving very slowly in the same direction as the current. So? Why should the movement of some background stuff affect the near-speed-of-light energy propagation passing through you?
Yes. Electricity moves at the speed of light[0] and like light will be constant no matter your reference frame.
[0] the speed of light in a given material and conditions. Generally it's a good fraction slower than light, but remember that light also moves slower through different materials.
Not sure why you're getting downvoted, this is an important point. The speed of light that is a constant is c. The actual (average) speed that light travels through a material is not a limit of any kind, and it is very possible for other particles to move through that medium faster than light. For example, Cherenkov radiation is high energy electrons moving faster than light through water (not faster than c).
Of course, what actually happens is that photons always move with speed c, but the path they take through a medium is not straight - they "bump" into other particles, so it takes them longer to reach the end. Higher energy particles can have straighter paths (they "push bumps away"), so that even if their instantaneous speed is always lower than the photons', they take less total time to move through the material.
Maybe the likening of superconductors and the cuprates resistance behavior is a clue.
Entirely speculative, but a larger scale analogy that I can relate to is a set of long pipes that fit together fairly well.
At low temperatures their entanglement (interaction with the rest of the universe) diminishes and they densify into a kind of crystalline arrangement that facilitates fairly unimpeded transfer of whatever energy flow really is; be it electrons, waves, or shifts of field energy in some form outside of my non-expert understanding.
At higher temperatures the material starts to jiggle, to expand, and to not quite align as well because everything's further apart and not quite right. This also causes more of the material to interact with energy that would have passed through at superconductive temperatures.
Maybe the packed pipes analogy is too far. A crystalline lattice where the interconnection between the components offers gaps could behave similarly in 3D space, or whatever N-dimension space might exist if that's something not just in science fiction.
Reflecting further, the densely packed (near absolute zero) conditions might also allow the 'strange material' to transition to a different sort of phase of matter. A state where individual components are packed together so tightly that they cease behaving as the groups we normally model and instead are interchangeable / intermingled with their neighbors. The electrons / waves could join the collective and dislodge a similar composition of material at a 'lower pressure'/'relief of potential' point.
the minimum breakdown voltage of distilled water under negative impulse at 2mm inter electrode gap spacing is 27kV with 14us breakdown time. The breakdown strength of distilled water is higher under positive impulse than negative impulse at same electrode gap spacing.
If the breakdown voltage for air were 10kV/cm, then that would imply pure water is a better insulator than air. Don't bet your life on it though!
It is, in my opinion, still "electrons". More pedantically, the electron field is still the mechanism for nonzero current, regardless of its exotic state. This must be the case as there's no other stable charge-carrying field that's not strongly localised to the nucleii (in this material, or any solid material I can think of). The article does a lot of waffling without admitting this basic point.
In the end, Chen, who successfully earned his doctorate in the spring and has since gone to work in finance, crafted a handful of nearly flawless nanowires.
Dumb layman question: why is there no mention of the Standard Model and what it would predict/simulate here? Is this too large-scale for that to be realistically usable?
Pretty much: directly solving the standard model quickly becomes intractable at much smaller scales. Most physics works with simplifications, like the Landau model mentioned in the article.
EG: "Feynman says that to be slavish to a received view or even to a method for discovering the facts means that we can never advance scientifically, for the old ‘facts’ may need to be overhauled in order to discover new ones, and how that may be done is, well, up for grabs."
In maxwell's equations, current density J is defined in terms of the E-field. When talking about electricity, people make the typical quantum mechanical wave-particle mistake. Electricity refers to two things, photons and electrons and how they interact with eachother. Both act as wave-particles, but photons act more like waves and electrons more like particles. The thing that gets people is that photons are the things that move energy around. A photon is an electromagnetic wave. In a wire, you can have an electromagnetic wave traversing the wire at some proportion of the speed of light, while the electrons are moving at speeds closer to meters per second. We defined current to be proportional to the E-field (because that is what is moving the energy) and thus we shouldn't refer to the movement of electrons as current.