Why do positive and negative charges attract?

1. May 9, 2010

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.

2. May 9, 2010

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.

Last edited by a moderator: Sep 25, 2014
3. May 9, 2010

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.

4. Jun 29, 2010

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?

5. Jun 29, 2010

nismaratwork

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.

6. Jun 30, 2010

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.

7. Jun 30, 2010

zonde

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.

8. Jun 30, 2010

Karmic Leprec

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.

9. Jun 30, 2010

nismaratwork

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...

10. Jun 30, 2010

Karmic Leprec

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.

11. Jun 30, 2010

alxm

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.

12. Jun 30, 2010

Karmic Leprec

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?

Last edited: Jun 30, 2010
13. Jun 30, 2010

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

Last edited: Jun 30, 2010
14. Jun 30, 2010

Karmic Leprec

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.

15. Jul 1, 2010

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)

16. Jul 1, 2010

nismaratwork

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.

17. Jul 1, 2010

phyzguy

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.

18. Jul 1, 2010

Karmic Leprec

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

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.

19. Jul 1, 2010

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.

20. Jul 1, 2010

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.

21. Jul 1, 2010

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.

22. Jul 1, 2010

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

Last edited: Jul 2, 2010
23. Jul 1, 2010

my_wan

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.

24. Jul 2, 2010

AJ Bentley

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

Or am I mistaken in that?

25. Jul 2, 2010

my_wan

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