Of course it isn't. The reason is energetic and related to the fact that electric charges are additive, so can have both signs.

Cf. also Article How Special Relativity Determines the Signs of the Nonrelati...

Thank you Stam for the answer and the paper, which looks very interesting.

Dear Jonghoon,

The electrical attraction of two electric charges of different sign is taken as a basic fact of electrodynamics. There is not an explanation and the different theories obviously always agree with it because is contained in them. One basic form to see how can work is if you calculate the stress Maxwell tensor in electrostatic for two charges and you would see what would be the force on the charges, this is a simple exercice made in the Panofsky and Phillips, Classical Electricity and Magnetism. That is not a proof but only tells you that the energy and the corresponding stress is in agreement with this experimental fact. The same happens with QED where the exchange of photons between two charges doesn't prove you this fact.

The above paper of Deser doesn't prove it at all. It would be very paradoxical that a theory of graviton/photon would explain this simple fact,i.e. we would need to have mass and electricity for explaining a pure basic electromagnetic result as the attraction or repulsion of electric charges.

Hi Daniel,

Thank you for your insightful answer.

It sounds like that physics is a science of description rather than of explanation.

Nonetheless the mutual agreement between math and physic is the beauty of nature in my opinion.

Electromagnetism is a gauge theory, i.e. it can be entirely derived from a principle of local invariance under a well defined transformation called U(1). If you derive electromagnetism that way there is no mistery about why opposite charges attract each other and charges with same sign repel, it is just due to the fact that electric charges interact via exchange of a photon which is a vector field. This is what you learn at uni in whatever course of advanced electromagnetism.

Alessandro, Your answer reminds me of the importance of electromagnetism in understanding the nature. Thanks.

Dear Jonghoon Kang,

If you really want to understand the underlaying forces of electro-magnetism; there is only one theory which gives simple and understandable answers and that is the Daon Theory.

Hi Stellan Gustafsson ,

I just quickly looked at the theory and it looks very interesting. Thank you for the information!

The electromagnetic (EM) field is a force field having direction. This means that there is implied a "from-to" relation. As pointed out in a comment above, the EM field is mediated by the exchange of photons. The photons are emitted "from" and travel "to". The convention is to represent "from" and "to" by the concept of "electric charge" and to use Benjamin Franklin's representation of "positive" and "negative" electric charge. Thus a photon travels "from" a charge of one sign "to" a charge of the opposite sign. This is a convention that assigns direction to the exchange of photons. With quarks we introduce "color" charge to represent the strong force's "from" and "to", that is, from "blue" to "red".

Dear Dwight,

The EM-field is not due to an exchange of photons, as was experimentally demonstrated by:

R. de Sangro, G. Finocchio, P. Patteri, M. Piccolo, G. Pizzella "Measuring Propagation speed of Coulomb Fields". arxiv:1211.2913 [gr-qc] 10/11-2014

Dear Jonghoon,

This is, ultimately, a philosophical question. We use abstractions whenever we can in order to aid understanding - for example, engineers are well aware of the “lumped matter circuit” - and we blackbox so many things so that we so often are unaware of how many presuppositions that we make, constantly. We can always question these presuppositions, question these black boxes, but most often we are given an explanation that, in itself, raises more black boxes. I assume that electrical attraction is ultimately derived from thermodynamic law(s), but don’t these laws, in themselves, raise further questions regarding explanation?

We would like it if there were some “ultimate foundation” upon which to build our knowledge; thereby guaranteeing certainty. Unfortunately, as Popper has said, we build our knowledge upon a swamp; the foundations can be questioned, and we can always ask further questions.

Personally, I like this, but one thing needs to be remembered: all things “above” the blackbox are, at least, approximately true. So, the black boxing of uncertainty, as we drive further down is, usually, reduced. After all, we can still send a rocket to the moon using Newton’s equations.

Dear Jonghoon,

You state: "Of course, Coulomb’s law describes the phenomenon, but that does not explain it, as far as I know. This may be a somewhat philosophical question."

I think you have it absolutely right.

It simply is a conclusively observed and measured "physical phenomenon", possibly the most fundamental law in the universe. Generalized by Gauss as his electric field equation, now referred to as Maxwell's first equation.

But close analysis reveals that opposite charges may not really be "attracted" to each other.

What seems to happen is that the Coulomb interaction adiabatically induces in opposite charges momentum energy oriented towards the other charge as a function of the inverse of the distance separating them, and it would be this momentum energy that causes them to tend to move toward each other. If the charges are of same sign, the momentum energy is induced oriented away from the other particle, which causes them to tend to move away from each other.

So, the Coulomb force would simply induce momentum energy in charges, momentum energy whose direction depends on whether the charges are same sign or opposite signs. It would be the induced momentum energy that causes the charges to move, not the Coulomb force.

Until any more fundamental law is discovered that could explain the existence of the Coulomb force, its nature can only remain a philosophical question for the time being.

Best Regards

André

Fields interact, and the physical geometry of the fields determines force.

If like charges attracted each other lightening could not strike, and a charged capacitor would not discharge when grounded. All the electrons would collect together in a few super clusters. Life could not exist in such a universe.

Its the anthropic argument, like charges must repel for us to be here to measure them.

Nobody ever said that electrons electrically attracted each other. It's been know for hundreds of years, since Coulomb discovered it, that "opposite signs electric charges" attract each other, not "same sign electric charges"

Particles do not have to be charged electrically. When they are, the like charges must repel and unlike charges must attract to support a living world.

Obviously for your second sentence. This is general knowledge. but since all massive elementary particles are electromagnetic in nature, they all have a charge by definition.

The answer is for a question why charges must attract. If they didn't then life as we know it would not exist, and the other alternatives would not support a living world either, except the one we have where unlike charges attract and like charges repel. The electric forces dominate our world including chemistry and biology without which we would not exist.

Absolutely. Why did you state then that "if charges attracted each other lightening could not strike, and a charged capacitor would not discharge when grounded"?

Opposite electric charges have to attract for this to happen.

Lightening strike was an extreme example, showing that like charges cannot attract, because there would be no electrical discharges. The other choices are either the charges generate no force which removes the reason for having charges, or opposites attract which is the only remaining choice. The question was why, and the answer is here.