Someone asked me a stumper: Why do protons carry a positive charge and electrons a negative charge?
To rephrase a bit, aside from the arbitrary designation of positive and negative, why do these two particles carry opposite charges?
I’m not sure that the question makes sense. Some particles have a positive charge, and others have a negative charge. The most common particles from each category were able to combine to form atoms. If this weren’t the case, the universe would be radically different, and we’d be discussing something else. Was this in the context of a religious discussion?
I have no idea whether the question even makes any sense; I’m not familiar enough with physics to tell. It wasn’t in the context of a religious discussion… I think it was just honest curiousity.
Actually, the question does make sense from a particular framework. Unfortunately, this is the same framework from which one can ask why there’s such a thing as electric charge at all. While some physicists may know enough to answer that question, I sure don’t.
It has been my observation that students are often quite surprised to find out how little we know about the very fundamental things that are encountered in introductory physics and chemistry classes. (Indeed, most students seem to be of the belief that “everything has been figured out.”) Examples:
–What exactly is charge, anyway? (Not to mention spin, strangeness, charm, bottomness, topness, etc.)
–Does the electron have any structure to it? It’s matter, and we know its mass, but what is its diameter?
–What is gravity?
–Is it a coincidence that the “inertial mass” and the “gravitational mass” of a given object are indistinguishable?
And so on…
On this subject, I wonder why the massive proton has a +1 charge and the very light electron a -1 charge. Of course we have positrons, with very light mass like elctrons, but with a +1 charge. Are there any massive (like protons)-1 chaged particles? If not, why not?
You bet. They are called anit-protons.
I was once in conversation about this with a bunch of mates down the pub; one of them (a very intelligent man), hadn’t said much, when the conversation reached a natural pause, he quietly said “you don’t really believe in electrons, do you?”
(We think he was referring to the electron/hole idea, but none of us dared to ask).
Of course not. Aren’t they really “greenies?” 
Check out Kenn Amdahl’s There Are No Electrons
Actually, the book didn’t do a whole lot for me. Cute, though.
This gets to be kind of philosophical question. Reminds me of the feminist claim that if men got pregnant, birth control would be easier to get, etc. But if men got pregnant, women would have penises and lots of testosterone and be calling the shots, and men would have estrogen and fighting for equal rights, and the men would be called women and the women would be called men and we’d be pretty much where we are right now.
Protons carry a positive charge and electons a negative because these particles have behavior that is most easily modeled by calling an attribute “charge” and arbitrarily saying one is negative and one positive. Physics, chemistry, and electronics all work just fine if you reverse negative and positive charge everywhere it appears.
I take that to be your question, more so than why we assigned negative to one and positive to the other. Why does charge exist, why do these two particles have opposite charge? Heavy questions, YAIAGAM (your answer is as good as mine).
In the areas of science and philosophy, if you keep asking “Why?” you’ll eventually reach “the end of the rope” where no answer exists or (at the very least) there is great debate. For example:
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Why do we exist?
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Why does the universe exist?
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Why does time exist?
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Why are there four dimensions?
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Why was Bill Clinton elected president?
I suspect the electron charge question falls into this category.
Actually, the question can be answered pretty simply. A proton consists of a certain group of quarks that yield a combined charge of +1, while the electron consists of a number of quarks that have a charge of -1.
However, that brings to the next level: Why do the quarks have the charge that they have?
Sorry, but electrons are fundamental particles, not composite particles (like protons). But the general thrust of Keith’s post is correct; we can “explain” proton charge by invoking the quark model, but that’s not really too terribly helpful.
Sweet! I get to be the first to answer some questions. Well,it’s true what they say- if you keep asking why,eventually you’ll get to the end of the rope and run out of answers. However, string theory explain mass and electric charge in a simple way. Of course, I don’t know how well string theory is playing out right now,but it seems sound to me. According to string theory all matter and energy is made of vibrating strings. The mass and charges are determined by how the string vibrates. They have even tried to explain why the vibrations work out the way they do, but it involes 11 dimensions and complicated geometrical shapes.
“Originally posted by Neurodoc
Are there any massive (like protons)-1 chaged particles?”
“You bet. They are called anit-protons”
I don’t think anti-protons are charge -1,are they? Well,I do happen to know there is a very massive particle called the muon that has a charge of -1, and an even more massive one whose name I’ve forgotten.
Depending on the level of detail one wants, these can be different questions or the same one. And physicists certainly agree that we at least have partial answers to all these questions. As is implicit in Dr.Lao’s answer, some of these questions and answers are tied up with the fact that for all types of particles there’s a corresponding antiparticle of opposite charge. The first question to ask is therefore:
- Why does matter outnumber antimatter ?
In a universe where there was the same amount of matter as antimatter, it’s conceivable that wevets wouldn’t have asked the question in this form. There’d be proton-mass particles and electron-mass ones, both positive and negative. We wouldn’t think of the electron-mass ones as particularly “negative”, though individual ones could be called negative. In the Standard Model of particle physics, there is an explanation of why this universe didn’t come to pass after the Big Bang. Due to an observed asymmetry called CP violation (and a number of other conditions), at a particular epoch during the very early history of the universe, positrons slightly tended to turn into electrons. And at the same time, antiquarks slightly tended to turn into quarks. End result: lots of quarks and electrons, which we call matter. Details can be argued over, but this basic picture is pretty standard. The second question is then:
- Given this, why are protons and electrons of opposite charge ?
Basically, charge conservation. There’s good observational evidence that the universe is electrically neutral overall. The total charge involved in the Big Bang thus appears to have been precisely zero. (Which, incidentally, is aesthetically nice …) The processes that are believed to produce the matter-antimatter asymmetry evidently violate various traditional (i.e. believed back in the Sixties) conservation laws, but they do respect charge conservation. It helps in this respect that the two processes mentioned above (electrons from antielectrons and quarks from antiquarks) are inter-related. As one turns positrons into electrons, anti-quarks are turning into quarks and positive charge is shifting from the positrons to the quarks. The end result is that the “electrons” wind up with a surplus of what we call the negative charge and the “quarks” have the positive charges. Slightly later on in the Big Bang, the quarks form baryons (and the odd meson). Crudely, in the everyday world, baryons are either protons or neutrons. The latter are neutral, so the protons are generally forced to be opposite in charge to the electrons. Hmm, but why exactly , so …
- Why are protons exactlyb opposite in charge to electrons ?
The answer here is currently rather more technical. One could imagine a universe where protons had 99 percent of the charge of electrons and there were just more of them kicking around in order to cover for charge conservation. The difficulty such a picture runs into is that the Standard Model has the property of being renormalisable. This is the whole business of quantum field theory being riddled with infinities and you’re having to cancel them. Now due to effects called anomalies, even the Standard Model (SM) in its most general form is not renormalisable. But it turns out that for particular choices of the charges of the particles involved, all the anomalies cancel. The rule is a simple summation over the charges in the theory. In the SM, particles come in groupings called families. (There are plenty of more complicated examples here, but Occam kicks in …) In the relevant one, these’s an up quark, a down quark, a neutrino and the electron. To get no anomalies these have to add together exactly as
3(2/3 - 1/3) + 0 - 1 = 0
The factor 3 reflects the fact that quarks come in three flavours. But the consequence that up quarks thus have 2/3 the negative charge of the electron and down quarks -1/3 of the same means that protons (uud) must have exactly the opposite charge to the electron.
Of course, this then just leads to the question of what’s so special about renormalisabilty ? Not so long ago, one would merely answer that with “show us a sensible theory.” But in recent years, the success of effective field theory has shown that sensible results can emerge from non-renormalisable theories. And it’s not so far from here that the “why” questions become research …
Correction to self: this should be “quarks come in three colours.” There are 6 flavours.
You sure you’re not taling about Skittles[sup]TM[/sup] now?
How big can a particle be, or how big is the biggest particle in diameter? I have heard that there are some very large ones or under certain conditions we don’t have on earth there are some very large ones. There was an April Fool’s Day item in one of the science magazines that showed a particle the size of a basketball and said it had just been discovered. Also, what color are the particles? I don’t mean quark color but actual color, like are protons and electrons and Xi’s and Higgses all black or different shades of gray?
The concept of colour has any meaning by the time you get to a sub-atomic level…
From the InfoPlease site.
Sub-atomic particles are too small to reflect coloured light which has a wavelength of between 350 nanometers and 800 nm (3.5^-7m to 8.0^-7m). An electron, by contrast has a radius of 2.8179409138^-15 m (according to this site), much to small to interfere with the passage of visible light…
Gp
Hmm, mind explaining how diodes work then?
When electrons switch energy levels, they do so by emitting or absorbing photons; so electrons can certainly interfere with light. Just so happens that color froms the light that electrons emit, which would make electrons whatever color we want, and color then (of course) has no meaning.
The color of quarks is just a property we assign. It helps to think of one infamous quote, “Something we don’t know is doing we don’t know what.” But, if we assign some trait-names to these things is sometimes helps to understand better, even if only by analogy.
If you try and think of “spin” directly in terms of rotation, things can get a little wierd, but it certainly does help “picture” what’s going on. But calling it “spin” is essentially arbitrary. They could have used any term they wanted. Some say we’d be better off without using words that already have meaning, that now the analogies actually impede thought. YMMV.
IIRC Quantum Chromodynamics is the study of quarks… and has been proven to have some strong explanitory power. But what I don’t know is if the color assignments have any analogy to real color thoery (addative and subtractive, etc). IIRC they do, so that particles have no color. Red must be paired with anti-red, or with green and blue (dunno if that is correct color-wise, just an example) so that the overall color of a quark-assembled particle has no color.
I would be suprised if there wasn’t a pretty strong analogy to normal color theory involved.