Electric force and photons

[Jacques]

I readed that the electric force is mediated by photons.

Can somebody explain that to me ?

For example two positively charged spheres repel each other. How photons exchanged between the spheres make them repel each other ? If you now have a positive and a negative charged spheres how does the same photon exchange mecanism make then attracted to each other ?

Thanks for your answers.

[Klaynos]

The four fundemental forces are probably mediated by exchange particles.

 

For the Electro Magnetic fundemental force this exchange particle is the photon.

[Jacques]

Yes but how is it working ?

[Severian]

An electron will emit a photon, which will be absorbed by another electron. The photon passes momentum from one elctron to the other.

 

It is a bit like firing a gun: since the bullet moves away at high speed it has lots of momentum, so the person who fired the gun feels a recoil and the person the bullet hits feels a push.

 

The gun analogy breaks down a bit when you have different charges attracting, but if you imagine that the bullet could carry negative momentum, then you can imagine that the photon can create an attractive force too.

[swansont]

Exchange forces

 

Feynman diagrams

 

Repulsion is easy - if you emit a photon, you recoil backward, and the same when you absorb it.

 

Attraction's a little tougher, conceptually.

attractive and more attractive explanations. Basically you have to get rid of your classical notion that the photon travels directly from one particle to the other, like two people throwing a ball back and forth that models the repulsive force.

[Jacques]

For a start let stick to repulsion.

How does the electron knows where to send the photon ?

If it is sent randomly in all directions, wouldn't the charge dissipate after a moment?

[Klaynos]

Photons have no charge, so they cannot dissipate the charge of an electron.

 

I belive they send them out in all directions, not sure though can't remember :s...

[Jacques]

You right photon have no charge so no charge lost. But there would be a lost in energy.

[swansont]

For a start let stick to repulsion.

How does the electron knows where to send the photon ?

If it is sent randomly in all directions' date=' wouldn't the charge dissipate after a moment?[/quote']

 

Please read the links I provided

[ydoaPs]

aren't they virtual particles? they wouldn't necesarily have to exist until they interact, right? like they can be in all directions, but only exist once interacting. gah, i can't explain what i am thinking. i have the idea in my head though....

[J.C.MacSwell]

Please read the links I provided

 

The boomerang analogy is brilliant!

[Jacques]

Virtual particle Humm It's like a phantom and everybody knows that phantom don't interact with matter

Does these explaination apply to macroscopic object ? Like the two metal leaf in an electroscope or the ballon I rubbed on my hair and is now stricking on the wall ?

[swansont]

Virtual particle Humm It's like a phantom and everybody knows that phantom don't interact with matter

 

"Nevah-theless" (Kate Hepburn in "The African Queen")

[MetaFrizzics]

The boomerang analogy is brilliant!

Not quite: Think about it:

 

(1) In the boomerang case, you have gravity, air, 3-dimensionality, and spin all working miraculously through effects like precession, lift, and complex exchanges with time over a large volume of spacetime to get the 'lucky' effect pictured.

 

Thus the analogy creates more questions than it solves, replacing a simple particle 'exchange' with a complex interaction requiring intermediary 'fields', extra time, and relatively large volumes of space as well as matter/energy to work against, in order to create the effect of a complex 'virtual machine' that can change the spacial direction of forces.

 

(2) The boomerang case fails as an actual experiment, since real boomerangs can't be set up to do this. At best the trajectory will be a tilted parabolic shape, directing the energy sideways rather than reversing the direction of a simple ball toss between floating boats. That is, to exchange boomerangs, they have to be thrown at a right angle to the direction between the boats.

 

While one might get 'lucky' in having a complex fluid motion of air that enables the successful toss (perhaps in the eye of a hurricane!) it is too strained an example.

 

(3) Better would be the analogy of firing a bullet in the opposite direction, with enough force to circle the earth in an orbit, striking the man in the other boat from the opposite side, like the Bugs Bunny cartoon where he throws a baseball around the earth to prove it is round. Note that this idea while physically possible, requires the Earth nearby, acting as a conversion engine for the direction of the trajectory.

[Jacques]

What I understand is that there are no simple explaination. We must do some act of faith...

That bring me to an other question: Does this model of particle exchange to carry the electromagnetic force, better than the electromagnetic field model (Maxwell)?

[J.C.MacSwell]

Not quite: Think about it:

 

(1) In the boomerang case' date=' you have gravity, air, 3-dimensionality, and spin all working miraculously through effects like precession, lift, and complex exchanges with time over a large volume of spacetime to get the 'lucky' effect pictured.

 

Thus the analogy creates more questions than it solves, replacing a simple particle 'exchange' with a complex interaction requiring [b']intermediary 'fields', extra time, and relatively large volumes of space as well as matter/energy to work against[/b], in order to create the effect of a complex 'virtual machine' that can change the spacial direction of forces.

 

(2) The boomerang case fails as an actual experiment, since real boomerangs can't be set up to do this. At best the trajectory will be a tilted parabolic shape, directing the energy sideways rather than reversing the direction of a simple ball toss between floating boats. That is, to exchange boomerangs, they have to be thrown at a right angle to the direction between the boats.

 

While one might get 'lucky' in having a complex fluid motion of air that enables the successful toss (perhaps in the eye of a hurricane!) it is too strained an example.

 

(3) Better would be the analogy of firing a bullet in the opposite direction, with enough force to circle the earth in an orbit, striking the man in the other boat from the opposite side, like the Bugs Bunny cartoon where he throws a baseball around the earth to prove it is round. Note that this idea while physically possible, requires the Earth nearby, acting as a conversion engine for the direction of the trajectory.

 

1. agree, but no analogy is perfect

 

2. mostly wrong, you can throw it in still air further "away" than at right angles and have it arrive from behind more than right angles and have a net force "pulling" the boats together, and a symmetrical clockwise throw will balance an anti-clockwise throw.

 

3. This is good also and if you prefer it great even though it requires "intermediary 'fields', extra time, and relatively large volumes of space as well as matter/energy to work against.".

 

Not that I have a problem with that and all analogies break down somewhere. A "perfect" analogy would not be an analogy, would it?

[MetaFrizzics]

What I understand is that there are no simple explaination. We must do some act of faith...

That bring me to an other question: Does this model of particle exchange to carry the electromagnetic force' date=' better than the electromagnetic field model (Maxwell)?[/quote']Right on both counts:

 

(1) There is currently no mechanistic model that can explain the 'force of attraction' found in Electromagnetic Theory (EM).

 

That in itself isn't really a problem, since QM and SRT have forced physicists to abandon simple materialistic/mechanical deterministic models of the real world generally.

 

The rub is in the fact that even with sophisticated field/particle theories, and Gauge theories, there is still no plausible 'cause/effect' style explanation for Attraction. Scientists can only point to it and go 'ooh. that looks like an attractive force'.

 

(2) Is the Maxwellian Formulation of EM better than say Quantum Electrodynamics (QED) ala' Feynman? Tough choices. Classical EM theory is elegant and simple in its concepts and mathematical structure, and much of the field theory is ported over to everything from the Weak Force to General Relativity in one form or another.

I personally prefer Weber's formulation, which is superior to Maxwell's in predicting and explaining certain electromagnetic forces and effects. Even Maxwell admired Weber's formulation. However Maxwell fell in love with Hamilton's quaternions, and he was lost to experimental physics ever since.

Not that I have a problem with that and all analogies break down somewhere. A "perfect" analogy would not be an analogy, would it?

You are right too. In fact both 'analogies' don't even act as analogies. Neither offers any plausible mechanism to explain attraction. It appears that any such explanation cannot do without postulating some kind of mechanism to convert the spacial direction of repulsive forces, which seem simply explained by the 3rd Law (Action/reaction)

[swansont]

Not quite: Think about it:

 

And we see that the danger of using analogies is that some people will read too much into them.

[MetaFrizzics]

In fact, the force of attraction is *not* a mystery, provided you are willing to put your money where your mouth is regarding physical laws:

 

(1) All known physical laws are time-reversable.

 

(2) Backward travelling particles simply explain the force of attraction.

 

(3) So Feynman believed, and his program of extension of QED to QM has been carried out successfully by Mead (Collective Electrodynamics -without Maxwell!) and Cramer (Transactional Interpretation of QM - backward particles & realistic causality)

[swansont]

In fact' date=' the force of attraction is *not* a mystery, provided you are willing to put your money where your mouth is regarding physical laws:

 

(1) All known physical laws are time-reversable.

[/quote']

 

CP violation in Kaon decays implies T-reversal symmetry is violated.

[Severian]

(2) Backward travelling particles simply explain the force of attraction.

 

A particle travelling backwards in time is an anti-particle. This has nothing to do with attractive forces.

[MetaFrizzics]

I didn't say there were no difficulties at all:

CP violation in Kaon decays implies T-reversal symmetry is violated.

One could approach this part of the problem two ways:

(a) There isn't enough hard evidence to force us to accept this calculation.

 

(b) The Standard Model is conceded to be flawed and incomplete anyway.

 

Work would remain to be done.

 

A particle travelling backwards in time is an anti-particle. This has nothing to do with attractive forces.

This is only one interpretation of Feynman diagrams and calculations. The interpretation is Dirac's. Feynman never really agreed to it, since he himself invented our most useful approach: Path Integrals over all routes. Feynman would have been the first to jettison 'anti-particles' in favour of a new interpretation that would explain attraction.

We should be at least half as creative!

[Jacques]

Is there some model for the electromagnetic force in the style of GR where gravity force is explain by space curvature. Is it possible to model the EM force with space curvature ?

Thanks

[MetaFrizzics]

Right now EM is incorporated in the exponents of the ten field equations. It seems to be a kludge of sorts, although it drops right in.

[Jacques]

"the ten field equations" sorry for my ignorance but is it a GR equation ?

"kludge" I am french speaking and didn't found a translation for that word... Do you have an other word for that

Thanks