[HN Gopher] Why does current flow the opposite way from the elec...
___________________________________________________________________
Why does current flow the opposite way from the electrons?
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.
Author : johncarlosbaez
Score : 191 points
Date : 2024-06-21 15:16 UTC (1 days ago)
(HTM) web link (mathstodon.xyz)
(TXT) w3m dump (mathstodon.xyz)
| NegativeLatency wrote:
| 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
| xdavidliu wrote:
| how is this recent? This was like 1900.
| gavindean90 wrote:
| That's more than a hundred years after Franklin.
| zer00eyz wrote:
| Rome was about 2500 years ago.
|
| The first recorded name, 5000 years.
|
| Oldest human structures 10k years.
|
| Humans, about 130k years.
|
| Our oldest "ancestors" 300-400k.
|
| 3.7 billion years.
|
| For you, not so recent. In the grand scheme of things it was
| a heartbeat ago.
| kevin_thibedeau wrote:
| The Nobel prize for proving the existence of molecules was
| awarded in 1926. Less than 100 years ago. Our understanding
| of physical chemistry is extremely recent.
| sethev wrote:
| The oldest living person today was born the same year Thomson
| published The Corpuscular Theory of Matter in 1907. So a long
| time ago in one sense, but not so long in the scheme of
| things.
| fhars wrote:
| 50% chance events happen all the time (well, half the time).
| drdec wrote:
| I think you were right the first time.
|
| If a particular 50% chance event does not happen, then the
| complementary 50% chance event does happen.
| nitwit005 wrote:
| 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.
| robocat wrote:
| The worst part is that up and down are not really opposites.
| Down is up on the other side of the world.
| technothrasher wrote:
| I'm not sure I follow you there. In that sense, "down" means
| toward the center of the gravity well. It is the same
| regardless of which side of the world you're on. If you mean
| that "down" changes direction with reference to a straight
| line, ok. But how does that make "up" not the opposite of it?
| crazygringo wrote:
| Up and down are opposites on the other side of the world
| too...
| manmal wrote:
| Or amino acids. Many have a D (Dextrorotatory = right) or L
| (Levorotatory = left) form, indicating into which direction
| they rotate polarized light.
| gerdesj wrote:
| dexter is Latin for right and sinister is left, rotatory is
| probably rotation and hat fit in with polarization.
|
| Where does levor... come from for left? Perhaps a newer Latin
| "left" than I was taught?
| gravescale wrote:
| It comes from the Latin "laevus".
|
| Funnily enough, although "sinister" came to mean "the bad
| side", it may have come from Proto-Indo-European for the
| "favourable side".
| ChainOfFools wrote:
| Knowing that ambidextrous thus means "both right (hands)"
| makes me marvel at how such a brazenly politically
| incorrect figure of speech has for so long remained
| undetected by the cultural police thanks to a linguistic
| camoflauge that mimics medical-sounding jargon.
| ooopdddddd wrote:
| Up and down quarks have names that make perfect sense, they are
| derived from the isospin which in turn derives from spin
| (spin-1/2 was the only other well-known object in physics that
| had the same symmetry properties). Which one is up and which
| one is down is the only arbitrary choice.
|
| Using "positive" and "negative" would have been a disaster.
| What charge does a positive antiquark have?
| CapitalistCartr wrote:
| 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.
| Gibbon1 wrote:
| Anytime electrochemistry is involved it's important. But
| regular electronics not very much. I think positive and
| negative mostly trips up people trying to use what they think
| is happening to explain theory. When it's not that useful most
| of the time.
|
| What I could never keep straight is anode and cathode.
| justhadto123094 wrote:
| CAThodes are PAWsitve
| g15jv2dp wrote:
| Cats are more intelligent than donkeys (ane in French).
| Cathode is positive, anode is negative. That's how I (and
| probably all French students) learned it.
| Thrymr wrote:
| A CRT display is a "cathode ray tube", which shoots
| electrons, which are negative.
| samatman wrote:
| It's easy! Cations are positively charged, so cathodes are,
| uh, negatively, charged. With anions and anodes it's the
| other way around.
|
| It makes perfect sense! Cations, you see, are attracted to
| anions. And reduced by cathodes. Anions? Attracted to
| cations. And oxidized by anodes.
|
| Whereas cations are oxidized by anions, and anions are
| reduced by cations.
|
| The only alternative here would be if cathodes and cations
| were positively charged, and anodes and anions were
| negatively charged. But then cathodes would reduce anions,
| and cations would also reduce anions. Even worse, anodes
| would oxidize cations, and anions would also oxidize cations.
|
| And we can't have that. It would just be too confusing.
| abecedarius wrote:
| The other day, I was reading a chemistry book at the point
| where it "helpfully" listed four different mnemonics for
| the same thing -- cations vs. anions, or maybe it was
| cathodes vs. anodes, or anyway, you know, _something_ in
| that vicinity.
|
| I just let my eyes skip over that list. I refuse to be the
| Jaguar in "Just-So Stories"
| https://etc.usf.edu/lit2go/79/just-so-stories/1294/the-
| begin...
| lukeasrodgers wrote:
| It doesn't help that very many explanations on the web of
| anode/cathode are wrong, or at least misleading, and _only_
| cover catalytic or galvanic cells.
|
| I believe https://chemistry.stackexchange.com/questions/16785
| /positive... is correct.
| ars wrote:
| Actually both wires are full of angry pixies, it's just that
| you have angry pixies in your body that match the ones in one
| of the wires, so you don't notice when you touch one, and
| strongly notice when you touch the other.
|
| On top of that if we did not ground one side of the electrical
| network, you could touch either wire and feel nothing. That's
| called an isolated ground, and is not commonly used except in
| hospitals and some other specialty settings.
|
| (If you wonder, we ground one side because if two different
| people both happened to touch a wire, current would flow
| between them using the each.)
| FLT8 wrote:
| I was under the impression that we primarily ground one side
| to prevent atmospheric charge and/or things like lightning
| strikes causing large voltage differentials to occur between
| power lines and grounded objects (it's probably a bit of a
| fire and safety risk if the wires coming into your house
| could be sitting many kV above earth potential).
| wongarsu wrote:
| Yes. If you have an electrical network that isn't grounded
| anywhere you can't get a shock from touching only one wire
| because there wouldn't be any current flow. If you repair
| electronics you might do that to a single device with an
| isolating transformer, or if you are a hospital you might
| do that to the entire building.
|
| But at the scale of a national grid it's basically
| impossible to ensure that the entire grid is isolated from
| the ground all the time. Stuff breaks. And if the network
| is grounded in some far away place but not anywhere near
| you you get exactly the effect you describe: you have some
| unknown and potentially large voltage differential towards
| ground because the literal ground doesn't have the same
| potential everywhere. So instead you give up and tie one of
| the potentials to ground, and do that as often as viable.
| SoftTalker wrote:
| The commonplace example of this would be a battery,
| correct? You can touch + or - separately and feel
| nothing.
| shepherdjerred wrote:
| I thought that was safe because the voltage/current isn't
| enough to go through skin or something like that.
| wongarsu wrote:
| For AA batteries that's true. But licking a 9V battery
| gives you a notable shock. Any wet skin should work to
| some degree at 9V, but the tongue is very sensitive so it
| brings the most dramatic effect.
| bmacho wrote:
| > 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.
| bmacho wrote:
| _Red and blue integers_ : there is red 1, red 2, ... 0, blue 1,
| blue 2, ... . Addition and subtraction as you expect. There is
| no ordering, also no multiplicative structure. There are 2
| isomorphism into the additive structure of the integers. ( _Red
| and blue reals_ are defined similarly.)
|
| I find this structure to model charge better. If not for else,
| at least it prevents you to ask silly questions about charge.
| hawski wrote:
| So you mean red like warm water and blue like colder? Warm is
| + and cold is -.
| crazygringo wrote:
| > _So you shouldn 't say "electron is negative". That's weird,
| confusing, misleading, and trolling._
|
| Huh? By the convention you describe (and we all share),
| electrons have negative charge, since -1 is negative. When
| speaking in the shared and understood context of charge, you
| shorten that to saying electrons are negative.
|
| Nothing weird, confusing, or misleading, and _certainly_ not
| trolling. I 'm baffled where you get that from.
| LgWoodenBadger wrote:
| He comes from an accounting background where commonly-
| understood terms mean the opposite of what everyone commonly
| understands them to mean.
| bmacho wrote:
| I am not sure what this means? Is this pure lies and
| insults? I don't see anything else here? In that case, fuck
| you very much :shrug:
| bmacho wrote:
| I mean I quoted baez, but I quote it again:
|
| > makes electrons negative
|
| It is not true, and trolling.
| crazygringo wrote:
| OK... so you've quoted them again.
|
| You still haven't explained why it isn't true, or why it's
| trolling. Just saying those things doesn't make them true.
|
| I can tell that English is not your native language from
| the number of grammatical errors you're making, so perhaps
| you're confused about something linguistic here?
| bmacho wrote:
| 1. the air is negative 2. the air's temperature
| is negative 3. the air's temperature is -1degC
| 1. the electron is negative 2. the electron's
| charge is negative 3. the electron's charge is -1
| p
|
| and there are more levels in between and with higher
| precision. But you see, the 3rd version is true, not
| confusing, not surprising. The 2nd version is somehow
| fishy, but accepted in practice, when people operate in
| good faith, and it does not create confusion. baez opted
| for the first version, which is not common, true, or
| acceptable. Only to create confusion, which is trolling.
| While pretending that this is a real problem, for the
| third version. It's not.
|
| I hope this answer is satisfactory, I hope to end this
| conversation, I don't like it.
| crazygringo wrote:
| Thank you for explaining your viewpoint. And I have to
| say I'm sorry, but you're just simply incorrect about
| this.
|
| Again, it's clear English isn't your native language, and
| I suspect you're simply making a mistake about how
| English is used. Which is not uncommon -- I've made
| plenty of mistakes thinking that how something worked
| conceptually in English would apply to another language
| too, and then being corrected by a native speaker.
|
| In English, it's perfectly conventional to say "the
| electron is negative" when you're talking about charge.
| It is linguistically and conceptually correct. There is
| nothing "fishy" and certainly nobody is "trolling", which
| is an unfair and uncharitable accusation for you to make.
|
| Perhaps it isn't correct to say in your native language,
| I don't know. I'm sorry you didn't like this
| conversation, but hopefully you can use it as a learning
| opportunity.
| dotnet00 wrote:
| I think you'll find that most people who would understand
| 2 and 3 would also understand the meaning of "the
| electron is negative" perfectly well, as humans (and at
| this point, probably LLMs too lol) can infer that the
| intent is to say 3, especially in this casual context of
| a social media discussion among normal people.
|
| It isn't like "the air is negative", which has many
| context dependent meanings.
| throwway120385 wrote:
| 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.
| akira2501 wrote:
| It really seems like had a rationale:
|
| "We suppose as aforesaid, That Electrical Fire is a common
| Element, of which every one of the three Persons abovementioned
| has his equal Share before any Operation is begun with the
| Tube. A who stands on Wax, and rubs the Tube, collects the
| Electrical Fire from himself into the Glass; and his
| Communication with the common Stock being cut off by the Wax,
| his Body is not again immediately supply'd. B, who stands upon
| Wax likewise, passing his Knuckle along near the Tube, receives
| the Fire which was collected by the Glass from A; and his
| Communication with the common Stock being likewise cutt off, he
| retains the additional Quantity received. to C, standing on the
| Floor, both appear to be electrised; for he having only the
| middle Quantity of Electrical Fire receives a Spark on
| approaching B, who has an over-quantity, but gives one to A,
| who has an under-quantity. If A and B touch each other, the
| Spark between them is stronger, because the Difference between
| them is greater. After such Touch, there is no Spark between
| either of them and C; because the Electrical Fire in all is
| reduced to the original Equality. If they touch while
| Electrising, the Equality is never destroyed, the Fire only
| circulating. Hence have arisen some new Terms among us. We say
| B (and other Bodies alike circumstanced) are electrised
| positively; A negatively: Or rather B is electrised plus and A
| minus. And we daily in our Experiments electrise Bodies plus or
| minus as we think proper. These Terms we may use till your
| Philosophers give us better. To electrise plus or minus, no
| more needs to be known than this; that the Parts of the Tube or
| Sphere, that are rub'd, do, in the Instant of the Friction,
| attract the Electrical Fire, and therefore take it from the
| Thing rubbing: the same Parts immediately, as the Friction upon
| them ceases, are disposed to give the Fire they have received,
| to any Body that has less. Thus you may circulate it, as Mr.
| Watson has shewn; You may also accumulate or subtract it upon,
| or from any Body, as you connect it with the Rubber or with the
| Receiver; the Communication with the common Stock being cut
| off."
|
| from Benjamin Franklin's letter to Peter Collison, May 25,
| 1747.
| throwway120385 wrote:
| But his choice of "positive" or "negative" are entirely a
| convention of how he wanted to think about things. There's
| nothing special about the sign other than it made it easier
| for him to reason about what was happening.
| wycy wrote:
| It's really strange reading the words of such an intelligent
| person beginning to understand something back then that is so
| fundamental today that even laypeople understand it more
| scientifically. Really weird, but really cool to get a peek
| back into a scientific mind in the 1700s.
| jstanley wrote:
| > even laypeople understand it more scientifically
|
| Laypeople use more scientific-sounding words, sure, but
| what more scientific way is there to _understand_ something
| than to have discovered it yourself through experiment?
| utensil4778 wrote:
| Experimentation brings knowledge, not understanding.
|
| Franklin did not _understand_ electricity, but merely
| observed it.
|
| It wasn't until we discovered the electron proper and
| Maxwell did his work that we-- anyone-- _understood_
| electricity.
|
| Understanding comes from scientific and academic rigor
| _after_ the discovery.
| detourdog wrote:
| I often prefer the original language of discovery. My
| favorite is the term accumulator compared to battery.
| somat wrote:
| That is a much better term, battery: inconsequential
| detail on how it is constructed. accumulator: what it
| does.
| a1445c8b wrote:
| Using the word "accumulator" wouldn't be enough to
| differentiate batteries from capacitors, inductors, etc.
| which are also accumulators.
| detourdog wrote:
| In system design that distinction may not matter.
| sudhirj wrote:
| Seems like capacitors, inductors and batteries differ
| only quantitively in their response curves, not in
| qualitatively? As in they all do different things to the
| circuit on the voltage, amperage and time axis? We would
| need separate words for them, but accumulators seems like
| a decent umbrella.
| B1FF_PSUVM wrote:
| > inductors, etc. which are also accumulators.
|
| In what sense do inductors accumulate?
|
| Batteries and capacitors accumulate (i.e. integrate)
| current.
|
| Inductors differentiate current: v = L di/dt means you
| get voltage out of current changes.
| TheOtherHobbes wrote:
| Inductors accumulate a magnetic field.
| utensil4778 wrote:
| The main way that inductors function is by storing energy
| in a magnetic field, exactly analogous to the way
| capacitors store energy in an electric field.
| mrunkel wrote:
| In German we use "Akku" which is short for "Akkumulator"
| for rechargeable batteries.
| ArnoVW wrote:
| Or 'pile' in French, which is homonym for 'stack' because
| a battery is a stack of alternating materials.
| lloeki wrote:
| interestingly "accu" in french is also used, but only for
| rechargeable batteries.
| catlikesshrimp wrote:
| Is that official? In spanish, decades ago, the word for
| battery was "Pila"
|
| "Pila" is a heap of countable physical units, either
| stacked or disordered. But pila is commonly a fixture for
| liquids, like septic tank is pila septica
|
| And batteries were mostly lead-acid. Hence, a pile for/of
| acid.
| IAmNotACellist wrote:
| TBH that's how I feel trying to intuitively understand and
| remember the various colors of quarks and their
| interactions.
| teraflop wrote:
| Along similar lines, I recently learned about an early
| nuclear physics textbook written by George Gamow. The first
| edition came out in 1931, and the preface of the second
| edition in 1937 describes how the book had to be completely
| written because the state of knowledge had changed so
| radically in those few years -- most notably, by the
| discovery of the neutron and of induced radioactivity.
|
| It's fun to think about a time when this stuff that we now
| take for granted as basic physics was not just new and
| poorly understood, but the forefront of knowledge was
| advancing so _rapidly_.
|
| I haven't been able to find an online copy of the 1931
| edition, but the 1937 edition is called _Structure of
| Atomic Nuclei and Nuclear Transformations_ , and it's
| available through the Internet Archive:
| https://archive.org/details/in.ernet.dli.2015.501245
| teraflop wrote:
| D'oh -- I meant to say "the book had to be completely
| _re_ written" but it's too late to edit my comment.
| freedomben wrote:
| Indeed! I love reading Benjamin Franklin for exaclty that.
| If you haven't read it, Walter Isaacson's biography on
| Franklin is absolutely fascinating. Brilliant, hilarious,
| driven, and wildly accomplished. The dude was (IMHO) one of
| the most interesting humans to have ever lived. Highly
| recommend.
| lupire wrote:
| This was how the 18th Century worked. In the 19th Century
| mathematical language became rigorous and formal, better
| able to handle more complex constructions accurately, but
| harder for lay people to learn, as it became a new
| language.
| kqr wrote:
| Well... going by the Fermi biography and the first few
| chapters of _The Idea Factory_ (about Bell Labs) I would
| think this is what it always sounds like in the early
| stages of humans discovering a new part of nature.
|
| It's just that our most recent theories have been so rich
| that we have happened to discover many things
| theoretically before we find them in real life. (Theory
| has preceded practice in recent decades, rather than the
| other way around which is historically more common.) I'm
| not sure this will always be so, it might be a temporary
| leap.
| card_zero wrote:
| Hmm. "We rub our Tubes with Buck Skin", he says in the same
| letter. I was trying to work out whether the tube gets a
| positive or negative charge. I think it depends on what
| material is being rubbed with what:
|
| https://en.wikipedia.org/wiki/File:Triboelectric-
| series_EN.s...
|
| The tube is glass, but is the buckskin fur, or slightly
| furry, or leathery? That would seem to alter the charge it
| gets.
| a1445c8b wrote:
| > Hmm. "We rub our Tubes with Buck Skin", he says in the
| same letter.
|
| My immature brain didn't get past this sentence.
| card_zero wrote:
| He was merely investigating what happen if persons touch
| one another after exciting the tube, on or off wax.
| cdelsolar wrote:
| Lol
| doodlebugging wrote:
| >We say B (and other Bodies alike circumstanced) are
| electrised positively; A negatively: Or rather B is
| electrised plus and A minus. And we daily in our Experiments
| electrise Bodies plus or minus as we think proper. These
| Terms we may use till your Philosophers give us better.
|
| Sounds like he leaves it open for future "Philosophers" to
| update the convention as our understanding of the phenomena
| that he had documented improved. Smart guy in not assuming
| that he got it right the first time. Franklin sounds like he
| wasn't a "my way or the highway" type of guy.
| dahart wrote:
| "These Terms we may use till your Philosophers give us
| better."
|
| Yes he had a rationale, the question is why it didn't change
| once we knew better; he even called for it.
|
| I mean, I think I know why it didn't change at any given
| point - the standard was already in place and it always looks
| too difficult. But in retrospect, the effort in the 1800s
| would have been small compared to the effort 100 years later.
|
| Maybe it's still true that we should change the convention
| starting now, because the confusion and cost of not changing
| it in the future will continue to grow?
| lupire wrote:
| There's no rationale, merely a decision. He chose Earth as
| the source of electric fire, instead of a sink. It's a
| completely arbitrary choice, as light source vs dark sucker.
| scotty79 wrote:
| He could have thought instead that A is collecting Electric
| Fire from the glass rod. And when B touches the rod they
| recharge it losing some of their Electric Fire.
| pdonis wrote:
| _> there is no way of knowing the direction of the charge_
|
| But there is--otherwise we wouldn't know that Franklin got it
| backwards. He thought the charge carriers were going one way,
| and chose the convention he did because he thought it matched
| the way the charge carriers were going, but it turns out they
| were going the other way. The signs of the charges are a
| convention--and the fact that we still use Franklin's
| convention and it works just fine attests to that--but the
| direction the charge carriers move is not.
| 2muchcoffeeman wrote:
| How would you have known this at first from rubbing rods and
| playing with static electricity?
| pdonis wrote:
| I didn't say we can know it just from rubbing rods and
| playing with static electricity. The post I was responding
| to said there is no way of knowing it, period. Which is
| clearly false since we _do_ know it now.
| dotnet00 wrote:
| I think they don't mean it in the literal "you physically
| can't tell the direction of charge at all" sense.
|
| As you say, the very fact that we know the real direction
| counters that. They mean that within the abstract context of
| electronics presented in introductory physics, the real
| direction of charge doesn't matter and cannot be determined.
| As long as you pick one consistent convention and stick to
| it, the math will always work out the same, since depending
| on convention, all the directions and signs are equally
| flipped. The real direction of charge only matters when you
| get deep into the details (eg semiconductors).
|
| At the level of detail of introductory physics, it's
| effectively a symmetry, similar to how given the simultaneous
| flipping of charge, parity and time, you cannot tell the
| difference.
| im3w1l wrote:
| I think there might be a difference. From our experience
| with air we know that blowing and sucking are not quite the
| same. Blown air has a much greater capacity for direction
| than sucked air. I would assume that this is because the
| when we blow we add additional molecules and we get to
| decide the inertia of those molecules, but when we suck we
| take away molecules and they have the inertia they have.
|
| I would suspect that the same goes for electrons.
|
| An electron gun would (as used in old CRT monitors), would
| be a very striking example of this - I doubt we could make
| an electron-hole gun (though shooting positive ions could
| work, but that's not quite the same thing) - but it may be
| possible to observe in more normal conditions too?
| denton-scratch wrote:
| Your hole-gun idea left me scratching my head.
|
| An electron gun produces a beam that contains only
| electrons; there is no conductor, and I think holes can
| exist only in the presence of a conductor. So you can't
| shoot a beam of holes through a vacuum. But if the
| material between the gun and the screen were a
| semiconductor, maybe you _could_ draw pictures on the
| screen using a beam of holes? I mean, I don 't see why a
| beam of holes can't be focused just like a beam of
| electrons.
| im3w1l wrote:
| > I mean, I don't see why a beam of holes can't be
| focused just like a beam of electrons.
|
| Wouldn't electrons rush in to fill the holes from every
| direction, rather than just the intended one? That's what
| my intuition says anyway. So yeah, my guess would be that
| it is in fact not possible.
| denton-scratch wrote:
| That blade cuts both ways; the electron beam in a CRT
| travels through a vacuum, there's nothing to "rush in". A
| hole beam would have to travel through a medium with no
| free electrons.
| denton-scratch wrote:
| > but it turns out they were going the other way
|
| Nobody seems to have mentioned Holes. Holes are positive
| charge-carriers. Yeah - they're virtual, they're not like
| positrons or protons. But they behave just like electrons
| going "the other way".
|
| My understanding is that a hole represents the absence of an
| electron. If an electron is removed (e.g. by rubbing),
| there's remains a physical object bearing a positive charge:
| the proton that was originally associated with that electron.
|
| I haven't heard anyone talking about holes for years. Are
| they now deemed an outmoded concept?
|
| [Edit: should have read further down the comments :-)]
| utensil4778 wrote:
| The concept of holes is important, but it doesn't have much
| practical use. It typically only comes up when you're
| discussing the physics of how semiconductors work, or doing
| similar electron-level analysis of a component.
|
| It's also usually brought up early on when teaching new
| students about circuit physics, but it's really not
| something that comes up in an EE's day to day.
|
| Maybe it's more relevant if you're deep into analog or RF
| black magic, I wouldn't know.
| jonny_eh wrote:
| In a way he was right, if he was describing the movement of
| "holes", or the lack of an electron.
| hn_throwaway_99 wrote:
| This is exactly why I think he was _wrong_. Normally, pretty
| much everywhere else we use the terms, "positive" denotes
| the presence or addition of something, while "negative"
| denotes the absence or subtraction.
|
| So while I agree with the GP's comment that Franklin didn't
| know anything about electrons, so he arbitrarily picked one
| as negative and the other as positive, now that we _do_ know
| about the movement of electrons, it kinda sucks because I
| think Franklin just "picked wrong".
|
| I.e. it would make much more sense to me if the _absence_ of
| electrons (i.e. holes) were negative by convention and an
| abundance of electrons were denoted as positive.
| throwway120385 wrote:
| This is pretty much spot on. It sucks after 250 years of
| hindsight, but I would encourage anyone who wants to think
| like Franklin to buy an amber rod, a glass rod, a piece of
| real fur, and a piece of silk, and try experimenting with
| them and see if you can intuit from physical experiment
| what the fire is made of and how it passes from one
| material to another. You can't without the benefit of
| future knowledge.
|
| This is what it feels like to stand on the shoulders of
| giants.
| hammock wrote:
| What is an amber rod?
| mindcrime wrote:
| Just what it sounds like: a rod made of amber[1].
|
| [1]: https://en.wikipedia.org/wiki/Amber
| mensetmanusman wrote:
| Not really, we talk about bubbles moving up, not water
| moving down.
|
| Current is bubbles.
| remram wrote:
| We do talk about water moving down though. There is no
| reason current should be bubbles.
|
| A rationalization after the fact is different from a
| reason.
| mensetmanusman wrote:
| In semi-conductor design discussions around transistors
| and motion of electrons, it's often much more convenient
| to talk about hole (bubble) migration than electron
| migration.
|
| It's really a moot point as to whether the abstraction
| used to solve problems matches with the physicalist
| interpretation of reality.
| throw0101d wrote:
| > _Numbers and numeric quantities aren 't a real thing that
| exists in the world. They exist only in our minds._
|
| Is math invented or discovered?
|
| * https://www.sfu.ca/~rpyke/cafe/livio.pdf
|
| See also "The Unreasonable Effectiveness of Mathematics in the
| Natural Sciences" by Wigner:
|
| *
| https://en.wikipedia.org/wiki/The_Unreasonable_Effectiveness...
| lazide wrote:
| Was 'Blue' invented or discovered?
|
| Fundamentally, it's the same type of problem - and really
| more of a philosophical thing.
| gavmor wrote:
| We're using the term "Blue" ambiguously.
|
| The _term_ was invented; its assignment and scope were
| invented, too. The wavelengths themselves were discovered.
|
| So there are two different "Blues;" signifier and
| signified.
| gavmor wrote:
| We're using the term "Blue" ambiguously.
|
| The _term_ was invented; its assignment and scope were
| invented, too. The wavelengths themselves were discovered.
|
| So there are two different "blues;" sigmifier, and
| signified.
| crote wrote:
| The interesting part is that perception is shaped by
| language. The Ancient Greeks did not have a word for blue,
| which led to things like the sky being described as "wine-
| colored" or "bronze". Similarly, the English "blue" is
| split into two in Russian: light blue (goluboi - goluboy)
| and deep/dark blue (sinii - siniy), a speaker _has_ to
| choose between them when describing something.
|
| The wavelengths may have always existed but colors only
| become a thing when we draw the arbitrary lines between
| them.
| labster wrote:
| In English, speakers are forced to make the same
| light/dark distinction between pink/red and orange/brown
| as well. I don't think most native speakers of English
| think of orange as the same as light brown.
| lazide wrote:
| Ah hah! This explains something.
|
| I've literally had an argument with someone where they
| insisted burnt umber was not orange or orange like.
|
| Which, uh - maybe? But c'mon. It's totally somewhat
| Orange!
| timschmidt wrote:
| Color perception depends on peculiarities of biology.
| Numbers and numeric quantities do not.
|
| The number of quarks in a proton or neutron is always 3.
|
| There are a fair number of dimensionless physical
| constants: https://en.wikipedia.org/wiki/Dimensionless_phys
| ical_constan...
|
| You can choose different number systems to represent the
| values symbolically, but the numbers will always be the
| same. At least in this universe.
|
| Wildly, parts of physics are only possible to describe
| adequately using imaginary numbers, which suggests that we
| could have chosen a better name for them:
| https://www.sciencenews.org/article/quantum-physics-
| imaginar...
| mensetmanusman wrote:
| "Numbers and numeric quantities aren't a real thing that exists
| in the world."
|
| How did your mind gain access to this universal truth? ;)
| philipov wrote:
| > We could just as easily have called it "black" or "white"
| charge
|
| And when we found a charge system that had 3 charges rather
| than just two, _we did_.
| lynndotpy wrote:
| Where can I learn more on this? Searching yields nothing.
| tekno45 wrote:
| https://youtu.be/AOtUo25GB3c?list=TLPQMjEwNjIwMjQajcfSE5215
| w
|
| Kinda
| warhorse10_9 wrote:
| Read up on "color charge."
| frutiger wrote:
| Quarks and gluons, or quantum chromodynamics
| bradboimler wrote:
| I imagine they're referring to
| https://en.m.wikipedia.org/wiki/Quantum_chromodynamics
| mr_mitm wrote:
| It's either six vs two, or three vs one, depending on what
| you mean by charge.
|
| The quarks and gluons can be red, blue, green, antired,
| antiblue, or antigreen.
| philipov wrote:
| I was _hoping_ someone would catch that ;)
| adrian_b wrote:
| The reason why which charge is named positive and which is
| named negative does not matter is because in all the equations
| that relate electric charge with other measurable physical
| quantities we never have an electric charge alone, but we
| always have the product of two electric charges.
|
| The value of the product of two electric charges is invariant
| to the convention chosen for the sign of the electric charge.
|
| Numbers and numeric quantities are actually a real thing that
| exists in the world. They do not exist only in our minds (and
| in the minds of many other animals who are also able to count
| until some small number). And so does the concept of negation,
| which clearly is a property of the world, independent of humans
| or animals.
|
| For other physical quantities, the sign of a quantity is not
| arbitrary, like for the electric charge, because those are used
| in expressions that are not invariant to sign changes.
| lupire wrote:
| Numbers do not exist in the world. Umbers exist outside the
| world.
| adrian_b wrote:
| I do not know if this is a joke about shadows that I did
| not get, or just a typo, but numbers exist in the world.
|
| The world is composed of things. The things are grouped in
| sets. Numbers are equivalence classes of sets.
|
| The set of the medium-sized planets of the Solar System is
| equivalent in number with the set of the big planets of the
| Solar System and also equivalent in number with the set of
| the big satellites of Jupiter (i.e. 4).
|
| Such equivalences between sets of things exist regardless
| if there are any sentient beings that recognize those
| equivalences and there are circumstances when for instance
| the evolution in time of some sets of things is determined
| or influenced by the relationship between the numbers of
| things that compose each set.
| juliushuijnk wrote:
| > The things are grouped in sets.
|
| By who?
| croes wrote:
| Our current universe
| adrian_b wrote:
| Even before the appearance of life, the things group in
| sets spontaneously, due to the interplay between
| attractive and repulsive forces and the positive
| feedbacks that appear in certain conditions.
|
| The world is not made of a homogeneous substance, but
| there are various kinds of groupings at various levels,
| nucleons and electrons group in atoms, atoms group in
| molecules, molecules group in pebbles, stars group in
| galaxies and so on.
| afiori wrote:
| Us?
|
| If one take the position tha minds are not part of the
| "real world" then you end up defining "reality" by some
| random model.
|
| It is just as absurd as saying that the only thing that
| exists is my own perception and you are "just" a ghost my
| mind is "thinking into existence".
|
| It sounds less crazy only because we are used to
| reductionism being generally more useful, but what is the
| usefullness of concepts like reality and existence when
| defined to mean that we and our minds (the only thing we
| perceive) are not "real" or do not really "exist"?
| bithive123 wrote:
| Negation, being a concept, exists only in the mind. Same with
| "things". A thing is a noun; a part of speech. The "real
| world" is undifferentiated quanta.
| joquarky wrote:
| Put simply, "the map is not the territory"
| trelane wrote:
| Or, as Monty Python has rightly pointed out, "it's only a
| model."
| adrian_b wrote:
| While in the mathematics of the later part of the 19th
| century and of the 20th century there have been developed
| many theories with very abstract concepts for which it may
| be claimed that those concepts have been invented in the
| minds of some mathematicians without a direct
| correspondence with the world experienced by them, such a
| claim would be false about almost any concept in the
| mathematics developed until the 19th century, because
| almost all older mathematical concepts are just
| abstractions of properties of the physical world.
|
| For instance, what happens when you connect the two
| electrodes of a battery to the pins of a semiconductor
| diode will differ depending on whether you negate the
| battery or not (i.e. you revert or not its connections).
| What happens with a ball (or with a thrown stone) will
| differ depending on whether its velocity is positive or
| negative, and so on.
|
| Additions and subtractions of physical quantities,
| therefore also negation, happen in the physical world
| regardless of the presence of sentient beings.
|
| Humans can recognize such properties of the world and give
| them names and integrate them in coherent mathematical
| models, but the base concepts are not inventions, they are
| the result of empirical observations.
| znkr wrote:
| Ceci n'est pas une pipe
| afiori wrote:
| I have an hard time coming to terms with this platonic view
| of the mind, as if our minds where some kind of
| extradimensional aliens playing with this sandbox of
| "undifferentiated quanta" sometime called reality.
|
| I understand how it make sense saying that the concept of
| spedrunning is completely absent in Ocarina Of Time and
| only exists in the player playing the game, but I do not
| see how this would be a good philosophy to apply to
| ourselves.
|
| I confess that I have a particular aversion to this
| specific philosophy/POV because I feel like it is riding on
| the respectability and "coolness" of science to sound more
| serious while being just another metaphysics without (IMHO)
| any* particularly good qualities.
|
| * Ok, I admit that it has at least a good quality: it is a
| good example of a non-religious metaphysics to give to
| people that cannot imagine a non-religious metaphysics.
| afiori wrote:
| There is a way in that it matters: in a vacuum tube you can
| have cathodic rays but (pragmatically) not anodic rays.
|
| IIRC a Veritasium video claims that these where essentially
| discovered by mistake in lightbulbs, so I suspect that
| Franklin would have had a hard time finding them...
| tzs wrote:
| Suppose that they had realized back then that electricity was
| going to become one of the most important technologies humans
| have in the future and decided that they should make a major
| effort to figure out the direction of the charge so future
| generations wouldn't get stuck with the wrong convention. All
| the top scientists, engineers, inventors, and crackpots in the
| world try to come up with some way to tell.
|
| Was there some method reasonably within their reach that would
| have worked?
|
| I'd guess the first thing they would try is weight. The body
| gaining the charge carriers should gain weight and the body
| supplying charge carriers should lose weight. That would
| probably fail because the mass of electrons is very low, and I
| don't think they had anything that could resolve weights that
| small. (I'm not even sure we have anything now that can do it).
|
| The second approach might again use weight, but with the
| realizing we don't have to measure what the weight is, just
| whether it has increased or decreased. So take two weights that
| are as identical as you can make them and put them on a
| balance. Seal the balance in an airtight container to prevent
| random air currents from disturbing it (or pump out the air--
| the vacuum pump was invented around 100 years earlier), and put
| it someplace very cold and with very little temperature
| variation, and adjust the masses until the balance shows no
| apparent movement for months. Then charge one of the masses and
| see if the balance can still remain apparently still for
| months. If it can't, and consistently goes out of balances
| toward the charged side conclude that side probably has the
| charge carriers. If it consistently goes toward the other side
| conclude that the charged side gave up charge carriers.
|
| I think that this too would probably fail. The mass difference
| is too small and isolating the balance sufficiently from
| outside disturbances is probably too difficult.
|
| Could they produce a stream of charges in a vacuum? Let's say
| they can. Considering the material they had to work with if
| those were negative they would probably be electrons and if
| they were positive they would probably be atoms or molecules
| with a missing electron.
|
| They would probably quickly discover that streams of charge in
| a vacuum are deflected when they bring a magnet near them and
| figure out that lighter charged things deflect more. They would
| then discover that all the negative charge streams they produce
| have carriers of the same mass, but the positive charge stream
| carries have different masses depending on how they are
| produced and they all have mass much greater than that of the
| negative carriers.
|
| I think they might lead them to conclude that the negative
| charge carriers are the fundamental ones.
| XorNot wrote:
| Thermionic electron emission in a vacuum tube would let you
| distinguish between electron and element: the electrons are
| liberated much more easily then the source material and
| result in current flow through the circuit.
|
| This lets you build diodes as a result, so assignment of
| electrical direction based on that phenomenon would get it
| correct.
|
| EDIT: in fact with a cathode ray tube you can literally
| visualise charge direction from looking at a foil wheel being
| spun in a vacuum: https://m.youtube.com/watch?v=K2G6M3cYJZs
| kabouseng wrote:
| Similar reason why the earth north pole is actually a magnetic
| south pole :) It was decided by convention / definition.
|
| For those whom it isn't clear what I mean. Compass magnet's
| north poles point north, which is only possible if the earth's
| north pole is magnetically a south pole.
| janto wrote:
| If anything, it's an issue with a magnet's naming. My
| understanding is that the North pole/direction got its name
| first.
| scotty79 wrote:
| > rods
|
| I think the origin might be phallic. Rod obviously gains
| positive charge when rubbed, for a man from 300 years ago.
| Am4TIfIsER0ppos wrote:
| 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?
| luyu_wu wrote:
| IMO the issue is that we used his convention even after we
| realized he was wrong. As a student, this trips me up
| immeasurably, especially after learning non-symmetric circuits.
| imchillyb wrote:
| 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.
| IAmNotACellist wrote:
| >It's fields all the way down.
|
| But what even IS a field, other than a thing through which
| scalar, tensor, or vector values can be expressed over some
| dimensionality? Also gravity.
|
| It seems at some point we have to just accept there's this
| currently irreducible thing permeating all of the thing we call
| everywhere.
| tdeck wrote:
| 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.
| pwg wrote:
| From reverse engineering a few low cost Chinese imports (i.e.,
| the 'odd brand names one finds on Amazon') I discovered that
| some Chinese engineers also design electronics using the
| convention of current flow from negative to positive.
| sobellian wrote:
| 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.
| tedk-42 wrote:
| Exactly this!
|
| Even the use of 'flow' is misleading. It's barely trickling
| through the wire...
| spaceywilly wrote:
| Exactly, I see many questions that start with "If the
| electrons are flowing from the negative terminal..."
|
| The movement of electrons is inconsequential. It's the
| magnetic fields between electrons that provide the power in
| an electric circuit. These fields actually don't even travel
| through the wires! They move around the space outside the
| wires. Ask anyone who has routed a differential signal pair
| :)
| arnarbi wrote:
| 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.
| boring-alterego wrote:
| 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.
| electrodank wrote:
| Any recommendations for the circuit books?
| daxfohl wrote:
| Same reason male seahorses get pregnant.
| jonny_eh wrote:
| This must make some people in Congress really angry.
| lioeters wrote:
| Wait until they hear about some mushrooms with more than
| twenty thousand genders.
| gerdesj wrote:
| No the males don't get pregnant or give birth. They brood, ie
| they look after the little ones.
|
| See the Reproduction section of:
| https://en.wikipedia.org/wiki/Seahorse for details
| hiccuphippo wrote:
| Relevant xkcd https://xkcd.com/567/
| xaellison wrote:
| came to comment this :)
| beryilma wrote:
| 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...
| gus_massa wrote:
| Those videos are misleading. Electrons flow inside the wires.
| They just flow much slower than what you would expect. When you
| close a circuit, the information that it was closed goes very
| fast but the electrons flow slowly.
|
| (It happens also with water, if you have the shower with only
| very hot water and you open the cold one, the output of the
| shower changes almost instantly but you need like a second to
| get the mixed water with that is warm.)
|
| What flows outside the wires is the energy. It's very
| unintuitive but it's true. Feynman has a nice lecture about it.
| But note that most of the energy flows very close arround the
| wires, a very small part wanders far away.
|
| There is an exception when you have a radio transmissor with an
| antena and a reciver. Then the energy flows just through the
| air (or vacuum). Also when you have a light lamp or a laser.
|
| Actualy every electric circuit emit some radiation as a bad
| radio tranmisor. But most of the times you can ignore it.
| int_19h wrote:
| The more straightforward analogy with water is a pipe that is
| completely filled. Even if the water moves very slowly, the
| fact that it has started moving is immediately detectable as
| some of it will start spilling from the other end of the pipe
| right away. If you have a turbine installed at the other end,
| it will also start spinning right away. Moreover, if you make
| the pipe wide enough, even very slowly moving water will move
| a lot of volume in a short period of time, and thus transmit
| a significant amount of energy to the turbine.
| sobellian wrote:
| Current really isn't flowing through the air. The relevant
| equation for resistive materials is J = sigma E; J is current
| density, E is the electric field, and sigma is resistivity.
| Air's resistivity is _huge_ - if you pump any significant
| current through air you will cause arcing.
|
| What really happens when you transmit energy through air is
| charge accumulation. Think of a parallel-plate capacitor -
| electrons accumulate on one side of the plate and holes on the
| other side. If you draw a black box around the system, it looks
| like current is flowing through it. But no significant current
| is actually going through the dielectric, or you will ruin the
| capacitor.
|
| Electrical engineers model the phenomenon that Veritasium
| pointed out as capacitive coupling. In a circuit diagram, we
| would literally just draw an additional capacitor in between
| the relevant circuit elements.
|
| In DC, this doesn't really matter after a certain settling time
| because the capacitor has settled to a certain charge. But in
| AC (or DC right after you flip the switch) it is non-
| negligible.
|
| Edited to add - to be clear, there IS an electric field in the
| air - but the current density is negligible unless you've
| caused dielectric breakdown.
| tim333 wrote:
| "are really fields per Maxwell equations" ignores quantum
| mechanics. Einstein got his Nobel prize for showing the fields
| interact as quanta such as photons and electrons. You can see
| the electrons doing their thing if you put them through a
| cathode ray tube as found in old analogue oscilloscopes
| verbalstoner wrote:
| That Veritasium video has been completely debunked by people
| dedicated to studying and especially working with electricity.
| Derek is a hack and you should look for real science channels,
| not popsci slop.
| AnotherGoodName wrote:
| 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.
| bequanna wrote:
| As a layperson, that makes sense to me. It also explains the
| time dilation effect when near a large mass.
| AnotherGoodName wrote:
| Thinking of it as directional action potentials that are
| blocked by mass? I agree it does feel intuitively nicer that
| way honestly.
| bequanna wrote:
| Yep. Coming from everywhere and moving outward in all
| directions at all times and 'absorbed' or 'blocked' by mass
| marmadukester39 wrote:
| Physicists: Has anyone ever looked into this?
| abecedarius wrote:
| Yes. https://en.wikipedia.org/wiki/Mechanical_explanation
| s_of_gra...
|
| (but I only play a physicist on HN)
| ViktorRay wrote:
| Well I guess that explains why "the normal force" is the one
| that counteracts gravity.
|
| (for those of you who don't know, the super simplified
| explanation in physics 101 is that the normal force is the
| vector that pushes up while gravity pushes down for objects
| that are resting on top of each other)
|
| So I guess the one who named it "the normal force" would be
| more correct that he ever imagined if your theory of gravity
| was the real correct one!
| hollerith wrote:
| Turn it into a theory that predicts exact _quantities_
| (accelerations) and I will start paying attention.
| ViktorRay wrote:
| Well why wouldn't it? The mathematical constants could remain
| the same as in the current theories.
|
| Both the constant G for gravitation and g for the
| acceleration for gravity on earth.
|
| I am not a physicist so I may be getting something wrong
| hollerith wrote:
| Newton's _Philosophiae Naturalis Principia Mathematica_
| (published 1687) contains a mathematical (geometric
| actually) proof that the gravitational attraction between
| the Earth an a man standing on the surface of the Earth is
| the same as it would be if all of the mass of the Earth
| were at its center. There 's another proof that if the man
| is standing at the bottom of a one-mile hole, and the Earth
| is assumed to be a perfect sphere, then the attraction is
| the same as if the Earth's radius were one mile less than
| it actually is (i.e., the attraction between the man and
| the shell of mass higher in altitude than the man is
| exactly zero because the attraction from the various points
| in the one-mile-thick shell exactly cancel out).
|
| That is that kind of thing I mean: proofs and calculations,
| not "why wouldn't it?"
| ViktorRay wrote:
| Hey thank you for your reply. I learned several
| interesting examples from your first paragraph in the
| comment.
|
| I do think your last sentence here was unnecessary
| though:
|
| _"That is that kind of thing I mean: proofs and
| calculations, not "why wouldn't it?""_
|
| When I said "why wouldn't it" I was asking out of genuine
| curiosity. There really wasn't any need to criticize that
| part. It came off as maybe more hostile than I think you
| intended.
|
| Again I most certainly appreciate you taking the time to
| type up the rest of your comment though because I did
| learn quite a bit from those examples you posted so I am
| indeed sincerely grateful for that.
| tzs wrote:
| The idea he's describing is Le Sage's theory of gravity, and
| it _does_ correctly predict many of the things Newtonian
| gravity predicts. Specifically it predicts an inverse square
| attraction between pairs of bodies and that the attraction is
| proportional to the masses of the bodies.
|
| It turns out it doesn't quite work, but it is interesting
| enough try that does get enough things right that quite a few
| well known physicists over the years have taken a look at it.
| The Wikipedia article on it covers a lot of them [1].
|
| Feynman talks about it briefly in section 7-7 of volume I of
| the Feynman lectures [2]:
|
| > Many mechanisms for gravitation have been suggested. It is
| interesting to consider one of these, which many people have
| thought of from time to time. At first, one is quite excited
| and happy when he "discovers" it, but he soon finds that it
| is not correct. It was first discovered about 1750. Suppose
| there were many particles moving in space at a very high
| speed in all directions and being only slightly absorbed in
| going through matter. When they are absorbed, they give an
| impulse to the earth. However, since there are as many going
| one way as another, the impulses all balance. But when the
| sun is nearby, the particles coming toward the earth through
| the sun are partially absorbed, so fewer of them are coming
| from the sun than are coming from the other side. Therefore,
| the earth feels a net impulse toward the sun and it does not
| take one long to see that it is inversely as the square of
| the distance--because of the variation of the solid angle
| that the sun subtends as we vary the distance. What is wrong
| with that machinery? It involves some new consequences which
| are not true. This particular idea has the following trouble:
| the earth, in moving around the sun, would impinge on more
| particles which are coming from its forward side than from
| its hind side (when you run in the rain, the rain in your
| face is stronger than that on the back of your head!).
| Therefore there would be more impulse given the earth from
| the front, and the earth would feel a resistance to motion
| and would be slowing up in its orbit. One can calculate how
| long it would take for the earth to stop as a result of this
| resistance, and it would not take long enough for the earth
| to still be in its orbit, so this mechanism does not work. No
| machinery has ever been invented that "explains" gravity
| without also predicting some other phenomenon that does not
| exist.
|
| [1] https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravi
| tat...
|
| [2] https://www.feynmanlectures.caltech.edu/I_07.html
| atahanacar wrote:
| What you are describing is a meme in my country, used to make
| fun of religious anti-evolution people who claim "evolution is
| only a theory and not a proven law, thus doesn't exist".
|
| We call gravity "yer cekimi", which literally means "the pull
| of ground". The meme is "Ya yer cekimi yoksa da gok itimi
| varsa?" which translates to "What if the gravity doesn't exist
| but sky-push does?".
| Joker_vD wrote:
| > 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.
|
| It would definitely surprise _me_ since I know that this theory
| -- since it 's such an obvious hypothesis -- has been proposed
| multiple times since Newton's own (it's now colloquially called
| "Le Sage's theory of gravitation" [0], but it had many other
| proponents including Kelvin, H. Lorentz and Thomson) and it has
| always failed to accomodate the equivalence of graviational and
| inertional masses: after all, the gravity is not proportional
| to the cross-section of the bodies, and graviational shielding
| does not exist -- experiments done by Eotvos were quite
| decisive in that regard.
|
| [0]
| https://en.wikipedia.org/wiki/Le_Sage%27s_theory_of_gravitat...
| loandbehold wrote:
| Do electrons actually flow when current moves? Apparently not
| https://youtu.be/bHIhgxav9LY
| bilsbie wrote:
| I've always wondered if there are any applications where it
| matters which way the electrons are going.
|
| Anyone know?
| tonyarkles wrote:
| Cathode Ray Tubes probably wouldn't work very well if they
| sucked electrons away from the screen instead of launching them
| towards it.
|
| At a deeper level it does start to matter when you get down to
| the physical level of transistors because electrons and holes
| (places in a crystal lattice where an electron could go but
| isn't there) move differently. P-type transistors generally
| can't be made as conductive as N-type transistors because, with
| plenty of handwaving, negative charge due excess electrons move
| easier than positive charge due to a lack of electrons.
| gus_massa wrote:
| https://en.wikipedia.org/wiki/Hall_effect If you put a magnetic
| field that is perpendicular to the current, you get a charge in
| one dide of the wires that depends on the moving charges. This
| is used to measure magnetic fields.
|
| https://en.wikipedia.org/wiki/Vacuum_tube usualy you heat only
| one electrode, but you must heat the correct one so electrons
| can jump to the other electrode.
|
| https://en.wikipedia.org/wiki/Cathode-ray_tube I'm not sure if
| it'a a different example or just a variation. Anyway, you can
| have a lot of fun changing the pressure of the gas, and the
| electric field
| https://www.daviddarling.info/encyclopedia/D/discharge_tube....
|
| https://en.wikipedia.org/wiki/Transistor IIRC they are also not
| symetric, but my knowdledge is too small even to write a good
| remark.
| marcosdumay wrote:
| > https://en.wikipedia.org/wiki/Transistor IIRC they are also
| not symetric
|
| They kinda are. Solid state conductors have those virtual
| particles called holes, that represent the global state of
| "having fewer electrons around here". You can have
| transistors where the electrons are carrying charge or where
| holes are.
|
| But the properties of holes and electrons are not completely
| symmetric. Holes disperse each other more strongly.
| Yaa101 wrote:
| 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.
| noobermin wrote:
| I was taught this in elementary school, I suppose not everyone
| knows.
| vagab0nd wrote:
| 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.
| soloist11 wrote:
| The theory of charges has Z/2 symmetry.
| lupire wrote:
| 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.
| michaelrpeskin wrote:
| 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.
| MarcScott wrote:
| 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.
| dboreham wrote:
| Always use Maxwell's corkscrew rule.
| thriftwy wrote:
| 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.
| mikewarot wrote:
| 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(
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