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Why does current flow the opposite way from the electrons?

by johncarlosbaez on 6/21/24, 3:16 PM with 242 comments

After fighting through a bunch of unhelpful answers, one gets to the bottom of things: Benjamin Franklin chose a convention that makes electrons negative, and apparently nobody knows why.
  • by throwway120385 on 6/21/24, 9:49 PM

    Because he didn't know anything about electrons, and the experiment he did involving rubbing amber and glass rods on fur and silk cloth only showed that something was transferred between the two materials, and that when the material containing the substance was brought near to the other material containing the other substance, the property conferred by the substances appeared to negate. If you read Teaching Introductory Physics the author very clearly points out that there is no way of knowing the direction of the charge. It must instead be decided by convention. And Franklin simply chose a convention that we stick with.

    This is where the need to use mathematical formalism to describe physical concepts becomes clear. Numbers and numeric quantities aren't a real thing that exists in the world. They exist only in our minds. And so does the concept of negation. Calling electrons "negative" is simply a tool for us to model how the substance behaves when it interacts with an "opposing" substance using numbers. We could just as easily have called it "black" or "white" charge, except that we then need to adapt arithmetic and algebra and calculus and so on to work with the concept of "black" or "white" quantities if we are to use them to understand the substance of charge.

  • by sobellian on 6/21/24, 10:03 PM

    Charge carriers aren't always electrons anyway, so you're restricting yourself by thinking of current as electrons moving. Even in the usual case where electrons are the charge carrier, it is only the small net movement of zillions of electrons back and forth which produces a current. So in any case current is a macrostate and electron movement is a microstate, and sign convention won't change that.
  • by CapitalistCartr on 6/21/24, 9:16 PM

    A big part of this is we measure what's important to us. As an electrician, what's important is which wire is full of angry pixies. They're technical direction of travel is far less important to my job (and my safety). When doing electronics, the direction of travel becomes quite important. So there's a different point of view.
  • by AnotherGoodName on 6/22/24, 12:29 AM

    It wouldn’t surprise me if at some point in the future we realise mass shields us from a gravitational field that pushes everything in all directions at once as opposed to our current thinking that mass emits a field that pulls us towards it.

    Eg. imagine the earth below you shielding you from a force that otherwise pushes all mass in all directions constantly. You’re now more shielded from the push in the direction of the earth so you feel pulled that way.

    It’s the same thing. Just a sign change from a convention we had no real basis to believe one way or the other.

  • by vagab0nd on 6/22/24, 3:26 PM

    The sign of the electron doesn't matter in this case. The definition of the direction of the current itself is also arbitrary. So are the definitions of positive and negative terminals. In fact, it is my understanding that most of the "left/right", "positive/negative", "north/south" definitions in EM are by convention. So the first guy calls it whatever they want and it doesn't matter at all.
  • by nitwit005 on 6/21/24, 9:11 PM

    Could be worse. They could have chosen any term implying opposite. We could have had left and right handed charges.

    Although I suppose we essentially did that when naming the quarks.

  • by lupire on 6/22/24, 3:48 PM

    This is really a type error.

    In some systems, there really is a positive. Such as temperature e with absolute 0, and where numbers multiply together into the same dimension so multiplication is not symmetric under sign change. (Although this is usually also a type error!)

    In other systems, there are a pair of opposite directions, and it's not correct to consider one positive one negative, but merely opposite. Both poles should be signed, and values never multiplied into the same dimension, and names distinctly, even if we must choose a convention when modeling them with computers.

  • by imchillyb on 6/21/24, 9:53 PM

    If one takes into account the field dynamics, the electrons are indicators of electromotive force and not the originator. The electromagnetic field connects the circuit and then _drags_ the electrons with it in a flow.

    Technically the opposite flow theory would be the opposite reaction to the field drag. Every action has an equal and opposite reaction. The equal reaction would be the electrons being dragged with the field. The opposite would be the current flow we observe.

    I can't wait until we can more clearly and accurately view the different fields that make up everything we know. It's fields all the way down.

  • by michaelrpeskin on 6/22/24, 4:38 PM

    This doesn't really answer the sign problem (which is just an arbitrarily chosen convention), but I view it more as "the field makes the electrons move".

    The rule of thumb I always use is that at household voltages and currents in copper the electrons move a few tens of microns per second. If your lights are on all day the electrons might move a meter or so from where they were when you turned the switch on.

  • by fhars on 6/21/24, 9:11 PM

    50% chance events happen all the time (well, half the time).
  • by Am4TIfIsER0ppos on 6/21/24, 9:51 PM

    Electrons were not discovered for more than a hundred years after his death. How could he have done the "right" thing other than by chance?
  • by beryilma on 6/22/24, 12:27 AM

    I dont understand all the details, but Veritasium and others on YouTube have videos on how the current/electron flow is also an illusion.

    Since electricity and magnetism are really fields per Maxwell equations, the current flow and other electrical things that we attribute to the inside of the wire are really happening outside of the wires as electric fields.

    They have a much better explanation than mine certainly...

  • by yarg on 6/23/24, 11:01 PM

    That explanation seems wrong - or rather it seems to address a completely unrelated question.

    The convention by which an electron is negative and a proton positive is arbitrary and could be flipped;

    Indeed it could be replaced by any pair of charge definitions x and !x.

    However that has zero impact on the direction of a current's flow through a conductor (that's a physical process and is not defined or impacted by the established conventions).

    I'm not sure what the real answer is, by my high school physics teacher told me that the charge is carried not by the electrons, but by the gap (a virtual particle) that flows backward as the electrons move forward.

    (Similar to the way that a gap in traffic propagates backwards.)

    I have no idea how wrong this is, so hopefully check the comment below from whoever bothered to correct me.

  • by daxfohl on 6/21/24, 10:59 PM

    Same reason male seahorses get pregnant.
  • by NegativeLatency on 6/21/24, 8:37 PM

    It was only relatively recently we figured started to understand some sort of model of what the inside of the atom is: https://en.wikipedia.org/wiki/Plum_pudding_model
  • by arnarbi on 6/21/24, 10:15 PM

    Others have answered correctly (it was an arbitrary choice), but fwiw I always found it helpful to think of current as the direction of the “holes” where electrons can be.

    Like bubbles rising in water, the holes “travel” opposite the potential that’s pulling the surrounding electrons the other way.

  • by tdeck on 6/21/24, 10:01 PM

    Everyone is giving correct answers so I'll just add something: in some parts of the world the convention has been to consider current flowing from negative to positive. For example in Scotland it's often taught that way apparently: https://www.mrsphysics.co.uk/blog/why-electron-flow-scotland...

    I read somewhere that this was also common in the USSR but can't find any references. Perhaps someone here will remember.

  • by MarcScott on 6/22/24, 5:14 PM

    I fondly remember watching kids in physics exams trying to answer questions using Felming's left hand rule. (https://en.wikipedia.org/wiki/Fleming's_left-hand_rule_for_m...

    You could watch them hold up both hands, wondering which one to use, then trying to dislocate their wrists as they aligned fingers and thumb with the diagram on the exam paper.

  • by DidYaWipe on 6/23/24, 5:16 AM

    This is great. I'm glad I'm not the only one this annoyed about the mixed messages in electronics. It really does mess you up as you try to learn and reason about how circuits work, when the first thing you learn in school is that electrons flow from negative to positive.
  • by Yaa101 on 6/22/24, 1:06 AM

    It does not, it just seems that way. The electron just jumps to an empty slot in the next atom (metals have empty electron slots in their atoms, that is why they conduct energy) and leaves a bit of energy in the current one. So if the electron jumps to the next atom on the right, the current seems to go left.
  • by boring-alterego on 6/21/24, 10:48 PM

    Fun fact when in 2 year school for electronics engineering technology we learned the current flow with the electrons, and in my 4 year electrical engineering school I learned it by following electron holes.

    You'll find basic electrical circuits books sometimes have an electron flow edition.

  • by mikewarot on 6/22/24, 7:32 PM

    It could be because in electroplating, metal flows from the positive terminal to the negative, because the metal ions are positive. However... electroplating wasn't invented until after his death.... oops. 8(
  • by kazinator on 6/22/24, 11:01 PM

    We don't even know why Ken Thompson chose ! for negation, and he is alive.
  • by loandbehold on 6/22/24, 12:30 AM

    Do electrons actually flow when current moves? Apparently not https://youtu.be/bHIhgxav9LY
  • by bmacho on 6/21/24, 9:17 PM

    > that makes electrons negative, and apparently nobody knows why

    When there is a symmetry, there are choices, all the time in math, and sometime in physics too.

    Also I don't like calling electrons negative, they are not. Maybe you can say that their charge is -1, when you model charge with the additive structure of real numbers / integers, and you choose the protons charge to correspond to 1. Modeling charge with the additive structure of real numbers / integers is very reasonable. (You could use red and blue numbers, but that's not a widely used structure.)

    So you shouldn't say "electron is negative". That's weird, confusing, misleading, and trolling.

  • by thriftwy on 6/22/24, 5:19 PM

    If you lick the positive pole of AA battery while touching the other end you get a sour taste. But there's no taste change when you do the opposite.
  • by Charon77 on 6/23/24, 4:44 AM

    Wait, but protons would be negatively charged and particle physicists are going to be angry about it?
  • by bilsbie on 6/22/24, 12:42 AM

    I’ve always wondered if there are any applications where it matters which way the electrons are going.

    Anyone know?

  • by noobermin on 6/22/24, 2:28 AM

    I was taught this in elementary school, I suppose not everyone knows.
  • by hiccuphippo on 6/21/24, 11:15 PM

    Relevant xkcd https://xkcd.com/567/