Why do positive and negative charges attract?

[Karmic Leprec]

These questions, being so basic, were harder to find answers to on the forums (or elsewhere). At least, it was harder to find an answer that satisfied my curiosity. I need a DEEPER, simpler, and more logical understanding of these concepts.:
What does it mean for a particle to have a positive or negative charge?

Why do positive and negative charges attract?

How would this apply to the Quantum model of electrons and protons in an atom?Thanks

*and trust me, deeper and simpler don't contradict each other by my definition. I'm sure most of you will understand.

 

[phyzguy]

Most of these types of "Why?" questions have no real answer other than "That's the way the universe works." Here is an excellent discussion from Richard Feynman on why the "Why?" questions are so difficult.

 

[haushofer]

Personally I like the treatment of Zee (QFT in a nutshell) in chapter 1.5. When exploring the path integral of the electromagnetic field you'll see that the EM-force between like charges is repulsive.

 

[Karmic Leprec]

Just trying to bring this thread back to life. I still need answers. I have thought this question over time and time again, and have come to no conclusion.
There is a real answer to this question. Maybe not the easiest answer to derive, but it exists, and I need to know it. Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?

 

[nismaratwork]

Just trying to bring this thread back to life. I still need answers. I have thought this question over time and time again, and have come to no conclusion.
There is a real answer to this question. Maybe not the easiest answer to derive, but it exists, and I need to know it. Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?

Why the certainty? Why is c the constant that it is? Physics identifies physical constants, but the "why" is the ken of philosophy or a more advanced theory. There is only a "how" answer to your question in this life Karmic.

 

[DrDu]

Personally, I agree with Hausdorffer that the book by Zee is very illuminating on that subject. At least, for the first time I saw an explanation as to why e.g. gravity is attractive between like masses while electromagnetism is repulsive between like charges.

 

[zonde]

There is a real answer to this question. Maybe not the easiest answer to derive, but it exists, and I need to know it. Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?

No, there isn't.
Particles do not need reasons to behave the way they do, they just do. All the possible answers to "why?" questions are invention of humans so they are not real in a deeper sense.

 

[Karmic Leprec]

Why the certainty? Why is c the constant that it is? Physics identifies physical constants, but the "why" is the ken of philosophy or a more advanced theory. There is only a "how" answer to your question in this life Karmic.

The constants are the charges of the particles. The question is, what causes these charges to react to each other the way they do.

Personally, I agree with Hausdorffer that the book by Zee is very illuminating on that subject. At least, for the first time I saw an explanation as to why e.g. gravity is attractive between like masses while electromagnetism is repulsive between like charges.

I understand why gravity is attractive and electromagnetism is repulsive. But the explanation for why those are, involves assuming that positive and negative charges react with each other the way they do. I have not read Zee, but I can easily imagine that he made this assumption as well.

No, there isn't.
Particles do not need reasons to behave the way they do, they just do. All the possible answers to "why?" questions are invention of humans so they are not real in a deeper sense.

Wrong. Most answers to "why?" questions are invention of humans, but there's always one answer which is true and real. For example, why does the sun rise and set? People have had thousands of answers to that question over thousands of years, yet only one answer is true and real. I am looking for that answer.

 

[nismaratwork]

The constants are the charges of the particles. The question is, what causes these charges to react to each other the way they do.



I understand why gravity is attractive and electromagnetism is repulsive. But the explanation for why those are, involves assuming that positive and negative charges react with each other the way they do. I have not read Zee, but I can easily imagine that he made this assumption as well.



Wrong. Most answers to "why?" questions are invention of humans, but there's always one answer which is true and real. For example, why does the sun rise and set? People have had thousands of answers to that question over thousands of years, yet only one answer is true and real. I am looking for that answer.

I'm sorry, but you're asking philosophical questions where they do not apply. The constants are the masses of elementary particles, c, and more. That they act in a particular way is a "HOW" not a "WHY" question, and has already been answered to some extent.

Why is there a universe, with physical constants? Who knows, that isn't physics. You can pretty much assume that when you say, "Why" instead of "How" you've left science. You don't have to like it, but your certainty that there must be a reason seems religious or dogmatic, and not justifiable.

The answer of course, is that the sun neither rises nor sets, or rather that it does both, and neither depending on your frame of reference. You're practically saying that you're looking for some absolute truth, and believe me that physics in general, and QM in particular is not the place for those. Only us theories here...

 

[Karmic Leprec]

I'm sorry, but you're asking philosophical questions where they do not apply. The constants are the masses of elementary particles, c, and more. That they act in a particular way is a "HOW" not a "WHY" question, and has already been answered to some extent.

Why is there a universe, with physical constants? Who knows, that isn't physics. You can pretty much assume that when you say, "Why" instead of "How" you've left science. You don't have to like it, but your certainty that there must be a reason seems religious or dogmatic, and not justifiable.

The answer of course, is that the sun neither rises nor sets, or rather that it does both, and neither depending on your frame of reference. You're practically saying that you're looking for some absolute truth, and believe me that physics in general, and QM in particular is not the place for those. Only us theories here...

When I ask "why?", it means the same thing to me as "how?" in this context. Only that, if I had asked how two particles attract or repel, people would tell me all about the results of the attraction or repulsion. I do not care for the results. I care for the cause. And the cause should be scientifically explainable.
Science without philosophy is experimental data without logical justification. Practical, but ignorant. Where science, philosophy and math converge is where great discoveries are made.

 

[alxm]

When I ask "why?", it means the same thing to me as "how?" in this context. Only that, if I had asked how two particles attract or repel, people would tell me all about the results of the attraction or repulsion. I do not care for the results. I care for the cause. And the cause should be scientifically explainable.

Did you watch the Feynman video linked to above? Nobody here can give a better answer than him, for reasons that he explains.

No 'why' or 'how' question is answerable unless you allow for something to be true. So you have to explain what context you intend the question to be answered in.

 

[Karmic Leprec]

Did you watch the Feynman video linked to above? Nobody here can give a better answer than him, for reasons that he explains.

No 'why' or 'how' question is answerable unless you allow for something to be true. So you have to explain what context you intend the question to be answered in.

Yes, I watched it. And just now re-watched it. I understand that this is a difficult question. And I understand NOW that it is an extremely difficult question. But just because Feynman couldn't answer it doesn't mean that there's not a single person out there that can't answer this question.
I agree with Feynman that there are numerous answers to the question, "why did the lady fall on the ice?", and therefor it is a difficult question to answer. However, I will take ANY legitimate answer to my question, because, frankly, I don't think anyone knows.

EDIT: As to what context I intend my question to be answered in? The mysteries of the Universe can either be solved forwards (from basic given laws that apply to everything undeniably), or backwards (logically inferring the cause of things based on the results of such causes). We can't go forwards, because we don't know or understand any law that governs the entire universe, so we must go backwards. So we are given that the charges of certain particles (or quarks/anti-quarks, for that matter), are of certain values. The results of their interaction are either attraction through space and over time between opposite charges or repulsion through space and over time between like charges. That is all I know. Now, is that all there is to know? Or am I missing some other aspects of the interaction?

 

[Kevin_Axion]

There will always be the question of "Why something is that it is", as humans, curiosity spoils the wonder and we search for an answer. This answer may be found easily or through complex actions- such as mathematics the easier questions would be answered through intuition. My point being, there is no reason to question why particles attract of opposite charges because the inevitable certainty becomes why is that true - ad infinitum. Once we reach a satisfying answer there are always more questions to ask and how are we so certain we aren't just naive beings who have created a false idea to merely satisfy our curiosity. In that I will say some questions are left to be unanswered and that is fine because it leaves us something to try to understand- that is how humanity grows we ask and wonder, we need these ideas to maintain our search for the true understanding of the universe

Here is a technical description of what we know currently: http://en.wikipedia.org/wiki/Quantum_Electrodynamics

 

[Karmic Leprec]

There will always be the question of "Why something is that it is", as humans, curiosity spoils the wonder and we search for an answer. This answer may be found easily or through complex actions- such as mathematics the easier questions would be answered through intuition. My point being, there is no reason to question why particles attract of opposite charges because the inevitable certainty becomes why is that true - ad infinitum. Once we reach a satisfying answer there are always more questions to ask and how are we so certain we aren't just naive beings who have created a false idea to merely satisfy our curiosity. In that I will say some questions are left to be unanswered and that is fine because it leaves us something to try to understand- that is how humanity grows we ask and wonder, we need these ideas to maintain our search for the true understanding of the universe

Here is a technical description of what we know currently: http://en.wikipedia.org/wiki/Quantum_Electrodynamics

I get what you all are saying. But at what point are we supposed to stop asking why? We could have stopped asking "why?" thousands of years ago, and likely we'd still be cavemen (or at least a lot less advanced than we are now). I want to know what is involved with these particles attracting and repelling, and, if the answer satisfies me, I can then decide if I want to ask "why?" that answer is the answer. Maybe others' curiosity is satisfied thinking that things "just are" in QM, but mine is not. Not by a long shot. I have lost sleep over this question, and I will eventually get an answer. All I am asking is for some help.

 

[Kevin_Axion]

Classically you can look at it that charge is an intrinsic property of particles and it's the way they disturb the electromagnetic field and the apparent interaction of these disturbed areas of the field are how the particles interact. I'm not an expert, you can learn Quantum Electrodynamics for a different and fundamental perspective, I believe that is the best we have in terms of certainty. Quantum Electrodynamics states that charges interact by exchanging virtual photons and this changes the state of the particle causing attraction or repulsion. You can include the field description but there is something about nature that is extraordinarily complex possibly absolutely simple that we don't have an answer for it. I'm sorry but I'm not sure anybody in the world has any knowledge of something this elemental and peculiar . Richard Feynman once said that "I think that I can safely say that nobody understands quantum mechanics." (Richard Feynman)

 

[nismaratwork]

I get what you all are saying. But at what point are we supposed to stop asking why? We could have stopped asking "why?" thousands of years ago, and likely we'd still be cavemen (or at least a lot less advanced than we are now). I want to know what is involved with these particles attracting and repelling, and, if the answer satisfies me, I can then decide if I want to ask "why?" that answer is the answer. Maybe others' curiosity is satisfied thinking that things "just are" in QM, but mine is not. Not by a long shot. I have lost sleep over this question, and I will eventually get an answer. All I am asking is for some help.

You don't have to stop asking why, you just have to stop believing that you are engaged in physics by doing so; recognize instead that you have entered the realm of philosophy.

 

[phyzguy]

I get what you all are saying. But at what point are we supposed to stop asking why? We could have stopped asking "why?" thousands of years ago, and likely we'd still be cavemen (or at least a lot less advanced than we are now). I want to know what is involved with these particles attracting and repelling, and, if the answer satisfies me, I can then decide if I want to ask "why?" that answer is the answer. Maybe others' curiosity is satisfied thinking that things "just are" in QM, but mine is not. Not by a long shot. I have lost sleep over this question, and I will eventually get an answer. All I am asking is for some help.

I don't think anyone is telling you to stop asking why. I wonder about these questions, too, and would love to have a better answer. What people are telling you is that nobody knows the answer to your question. Maybe you can figure it out and enlighten the rest of us.

 

[Karmic Leprec]

Quantum Electrodynamics states that charges interact by exchanging virtual photons and this changes the state of the particle causing attraction or repulsion.

Can anyone elaborate on this? What are virtual photons? How are they exchanged? What is the nature of the virtual photon exchange that let's us define the interaction as either attraction or repulsion?

You don't have to stop asking why, you just have to stop believing that you are engaged in physics by doing so; recognize instead that you have entered the realm of philosophy.

I recognize that I am asking a philosophical question about physics. I can't think of anyone better to answer my question than people who know a lot about physics.

 

[Phrak]

When I ask "why?", it means the same thing to me as "how?" in this context.

Yes. But you get a different quality answers when you use the 'how' word.

 

[yossell]

One can keep asking why as long as one wants. Nobody forbids it. Sometimes, it can lead to great new discoveries. Sometimes, it leads nowhere.

But it's also perfectly all right if a theory takes certain things as fundamental, incapable of further explanation. If we've reached bedrock, we shouldn't expect a further, more fundamental answer. All theories have their bedrocks - whether it be that unaccelerated particles travel along straight lines, or that the speed of light is constant in all inertial frames, or that the Lorentz transformations are a fundamental symmetry of the laws.

It's always exciting when a new theory comes along and explains things that were taken as primitive before. But it too will have its primitives - a point where it says: this is just how things are.

Why questions are always welcome - but just because a theory can't provide an interesting answer to a why question is not, in and of itself, a problem for the theory.

 

[Kevin_Axion]

Here's an in depth nature of how electromagnetic interactions occur in elementary particles:
http://en.wikipedia.org/wiki/Quantum_Electrodynamics
This link will provide the appropriate outline necessary to understand electromagnetism including virtual photons and fermion interaction via boson exchange.

 

[unusualname]

The modern explanation is derived mathematically from QFT which shows that the exchange of a spin 1 particle (photon) produces a repulsive force, and spin 0 (pions, nuclear force) and spin 2 (gravitons) produce an attractive force

The derivation finds a +ve potential energy term between two lumps of (the same) charge (and -ve term for opposite charges, hence attraction)

eg for a simplified treatment see chapter I.5 in Zee's Quantum Theory in a Nutshell (unfortunately the google book is cut near the end of the relevant chapter)

The best answer you'll get atm is a mathematical one, since our physics models at this scale are purely mathematical.

I must admit, that ever since I was very young I have been fascinated by the repulsive force between two magnets, and even today find it a little frustrating to have the effect described rather esoterically as virtual particle exchanges.

I hope that string theory will show that the particle exchanges are the result of "ripples" in spacetime and the repulsive effect will be found to be the actual resistance of spacetime fabric to "compression" (and attraction due to resistance to "stretching"), which would be easier to explain to a young child, but we'll have to wait a few more years

 

[my_wan]

Wrong. Most answers to "why?" questions are invention of humans, but there's always one answer which is true and real. For example, why does the sun rise and set? People have had thousands of answers to that question over thousands of years, yet only one answer is true and real. I am looking for that answer.

No, answers do not involve only one true and real answer. Science often finds that the same answer can be derived from seemingly unrelated descriptions. The one "true" answer is a psychological illusion.

As the video of Feynman that phyzguy linked said, the answer is: for the same reason you can't walk through walls.

 

[AJ Bentley]

Fascinating, I've never seen the 'Why?' game being played by an adult before.

Or am I mistaken in that?

 

[my_wan]

Maybe we should start a 'why' game in general discussion. Then link to there every time the 'why' question comes up.

 

[Academic]

You guys are giving some good answers, my first thought was the cop out answer. Positive and negative charges attract because they are defined that way. Not very satisfactory, I know - but in the end I think that is about as good as it gets.

 

[Faradave]

Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?...

I understand NOW that it is an extremely difficult question…

We could have stopped asking "why?" thousands of years ago, and likely we'd still be cavemen… I have lost sleep over this question, and I will eventually get an answer.

Can anyone elaborate on this? What are virtual photons? How are they exchanged? What is the nature of the virtual photon exchange that let's us define the interaction as either attraction or repulsion?...

Karmic, it’s time for a reality check. I’m sure that folks here have given you their sincere best. But as someone who has also lost sleep over the mechanism of attraction, let me reassure you that your question is clear and reasonable. It’s our current state of knowledge that stinks. That’s why we see more dancing in this thread than at the Bolshoi Ballet Academy.

I don’t want to offend anyone, especially those kind enough to attempt an answer, but we’re never going to get a better answer if we don’t admit that the one we have is horrible, disgusting, unsatisfactory and obviously wrong. But it is nevertheless a starting point and like most of the really cool explanations now offered by physics, this one comes from very humble beginnings.

In my travels, I found pretty concise answers to your questions at http://math.ucr.edu/home/baez/physics/Quantum/virtual_particles.html The first topic is "What are virtual particles?" the next is "How can they be responsible for attractive forces?"

As an outsider to physics, one thing I’ve learned is to watch out for expressions like, “All we have to do is…” because you’re about to get stretched to the breaking point. Taking electrostatic repulsion between two like charges for example. All we have to do is… use the uncertainty principle to borrow energy from the vacuum and create undetectable virtual photons. These are exchanged between like charges as if you and I were throwing a heavy ball back and forth between us. When I throw the ball at you, I recoil back from it and when you catch it you get a push away from me. Voila! Repulsion! Got it?

If you could walk away with just that, everyone could go on with their happy lives. But you had to go and ask about ATTRACTION. That seems to makes you an ignorant, childishly demanding, philosophizing, zealot! How dare you?

Well, it’s all very simple really. All we have to do is... push the uncertainty principle so far that we can’t tell where the virtual photons are coming from or going. Then suppose that a virtual photon is actually emitted from the “absorbing” electron and received by the “emitting” electron and since it happens to travel backward in time, it has negative momentum and there you have it, attraction. Now you see why even Dr. Feynman didn’t want to admit this in a live interview. It's far simpler to blame the questioner for being too ignorant to know not to ask that question.

Remember:
1. It’s just a model.
2. It can only improve from here.
3. Never stop asking why. Mysteries are only mysteries till they’re not.

 

[Glen Bartusch]

Just trying to bring this thread back to life. I still need answers. I have thought this question over time and time again, and have come to no conclusion.
There is a real answer to this question. Maybe not the easiest answer to derive, but it exists, and I need to know it. Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?

There really is no such thing as absolute charge, and that our convention of assigning "positive" or "negative" to charges that repel and attract is just for convenience.

For example, if you have two positive charges near each other, they will repel. Somewhere else, you have two negative charges next to each other. They likewise will repel one-another.
But mix all four together, and two + charges will attract the two - charges.

If you separate all four, you will not be able to distinguish between what's positive and what's negative. The best you can do is say that "one will attract another, and repel the third. The fourth charged particle will do the same. However, I no longer know which was positive and which was negative."

 

[orienst]

Just trying to bring this thread back to life. I still need answers. I have thought this question over time and time again, and have come to no conclusion.
There is a real answer to this question. Maybe not the easiest answer to derive, but it exists, and I need to know it. Please tell me, why do opposite charges (specifically positive and negative sub-particles) attract?

Law of Gravity！Why？

 

[Kevin_Axion]

If you are defining the inverse square law then yes, electromagnetism contains a symmetric law to gravity but to say that opposite charges attract and repel via the Law of Gravity is clearly incorrect. Electromagnetism is described by Quantum Interpretation - Quantum Electrodynamics. Quantum Electrodynamics doesn't define that the Law of Gravity is inherent in theoretical reasoning in fact Gravity is of a distinctive nature. Gravity according to General Relativity is the curvature of spacetime rather Electromagnetism is the distortion of the electromagnetic field which interacts with fermions via boson exchange - photons. Conceptually the gravitational force is mediated via boson exchange of gravitons - hypothetical particles described in Supergravity and in Superstring Theory/M-Theory.
Graviton
Spin: 2
Mass: 0
Photon
Spin: 1
Mass: 0
Obviously there must be a discrepancy in your reasoning if you define the nature of electromagnetic interactions to be caused by the Law of Gravity.

 

[DrDu]

I don't think that positive and negative charges are primarily defined that way because they attract.
Methodically I can study the status of attraction and repulsion of a test charge in the field of another charge. Using different kinds of test charges (You know, these experiments of rubbing glas rods with silk and sulfur spheres with cats fur) one found that there are two kinds of charges behaving differently. One assigned them arbitrarily "+" and "-".
In a next step one can compare two test charges which behaved the same way. It is not clear a priori whether they attract or repell. In the case of electromagnetism one found that they repell.

 

[adaptation]

Thanks Faradave. Awesome explanation. Good link. I totally agree with you about the "answers" we currently have.

I think we've gone quite too far with our "All we have to do is..."-ing. Thankfully, we keep asking "Why? Why? Why?" Someday we may have some more satisfying answers.

 

[DrDu]

I'd like to bring up this topic again, as I am not too content with the explanations offered.
The effect of attraction does happen not only for elementary particles but also for macroscopic objects whence quantum effects do not seem to be essential for an understanding. That the exchange of particles leads to attraction or repulsion is also not peculiar to relativistic field theories, e.g., the attraction which leads to bound cooper pairs in superconductors is due to the exchange of phonons in this language.
As I already stated, I like the approach of Zee who both showed how attraction and repulsion between like charges alternates with spin increasing from 0 over 1 to 2.
Zee also uses the mattress model as a toy field theory. If we can understand how attraction does occur in that model, we also understand the basic mechanism in more realistic field theories.
That two like sources attract on a mattress is probably known to everyone who has ever slept together with some other person in a bad hotel bed: The own weight acts F as a source of displacement of the springs of the mattress with the displacement u of the springs corresponding to the field variable. That is, we have a potential energy term $$-F_i u_i$$. Evidently, we could describe the displacement u due to our source as a superposition of virtual particles of all wavevectors k and of frequency omega=0, but that would be quite an overkill. That there are springs at all means that we are dealing with a massive field theory as the potential energy contains a term 1/2 k u^2, k being the force constant of the spring. The springs are also coupled together which is the true source of our dismay. There is a potential energy term proportional to $$1/2 k'(\Delta u_{i j})^2$$ between springs at positions i and j being neighbours. In a continuous field model, we would have to replace the difference by the gradient of the field. The source term will lead to an excursion at point i which will lead to an energy gain. Due to the coupling of the springs, other points j will have to follow to reduce the gradient of displacement although there preferred equilibrium position is at u=0. If we bring another source close to the first source, we can decrease the gradient whence attraction results. The contrary would be true for a source of different sign, e.g. putting a helium balloon under the bed. As the displacement due to the sources points in different directions, the gradient will be the larger the closer the two sources approach whence they mutually repell.
That's the basic mechanism.

I also tried to understand where the difference between particles with spin 0 and spin 1 as in electromagnetism comes from. The calculation in Zee's book involving the path integral is quite an overkill. As long as we do not have to fight against relativistic enemies, we could look at the Hamiltonian instead of the Lagrangian and obtain the energy from it.
In the matrace model, the Hamiltonian is the sum of kinetic and potential energy, T and V,respectively, with $$T=\sum_i1/2 (\partial_t u_i)^2$$ and $$V=\sum_i 1/2 k u_i^2+\sum_{ij,\; neighbours} 1/2 k'(\Delta u_{i j})^2 -F_k u_k -F_l u_l$$.
In electromagnetism things appear similar on the first view. Let's first consider the situation without sources. Then we can chose phi=0 and L=(E^2-B^2)/2, where $$E=-\partial_t A$$ and B is the rotation of A. Hence the term E^2 corresponds to kinetic energy and B^2 to potential energy. In the case with sources, something strange happens: The definition of E now becomes E=-\partial_t A-\grad \Phi [/tex]. In the electrostatic case A=0, $$L=E^2/2+\rho \Phi$$ with $$E=-\grad \Phi$$ and we find that the potential energy of the electric field now forms part of the kinetic energy. Now the Hamiltonian density is $$H=E \partial_t A -L=0-E^2/2-\rho\Phi$$. Comparing this with the spin 0 case, we see that the gradient of the field variable (Phi) has a stabilizing instead of a destabilizing effect!
Obviously we get a more usual expression for the Hamiltonian density making use of $$\nabla E=\rho$$ so that on partial integration of the source term we get $$H=-E^2/2-\rho\Phi =-E^2/2+E^2=E^2/2$$

 

[Andrey]

These questions, being so basic, were harder to find answers to on the forums (or elsewhere). At least, it was harder to find an answer that satisfied my curiosity. I need a DEEPER, simpler, and more logical understanding of these concepts.:
What does it mean for a particle to have a positive or negative charge?

Why do positive and negative charges attract?

How would this apply to the Quantum model of electrons and protons in an atom?


Thanks

*and trust me, deeper and simpler don't contradict each other by my definition. I'm sure most of you will understand.

They attract because that's how information between them is exchanged.

 

[ankitkumar]

let me give you an exercise. practise it daily on different things. like begin with a tree and ask the question "why" based on any property of the tree. for e.g why does tree give oxygen? answer it and then again ask the question "why" till you go on and on. ok.


coming to your question, "why do positive and negative charges attract?".
they attract so as to reach the state of minimum enrgy. every matter of the universe escalates towards the condition of minimum energy. it is not a law, not a property. it is only the behaviour. for e.g we rest at night and that is the position of minimum energy.
in a broader sense, the state of minimum energy is the point of no creation. at the point of no creation there will be nothing.

this has a more elaborate explanation but i hope u ud be satisfied with this. if you want more just reply me.