# Quantum Electrodynamics

1. Aug 28, 2004

### colinr

I have a book talking about transient electron-positron pairs appearing and disappearing inside a hydrogen atom which effects the attractive force between the proton and the electron, okay I'm fine with that.

It then goes on to say that the effect is only over short distances because of the speed of light. Does this mean that the electric force of attraction propagates as an elctromagnetic wave?

2. Aug 28, 2004

### Gonzolo

I'm not familiar with pairs occuring an atom, but any moving electric field creates an EM wave, that's what electrodynamics is mostly about. That is why the cells in your eye respond to the light from your monitor. Electric charges in your monitor move, creating EM waves that reach your eyes, moving charges in them that makes a current reach you brain. An EM wave is a wave of E fields (and corresponding B fields) just like the attractive and repulsive ones you know about.

3. Aug 28, 2004

### colinr

so their effect can only have travelled as far as the em wave produced by the moving charge could have travelled in the time the pair existed.

the attractive force is a property of the wave

Thanks

4. Aug 28, 2004

### what_are_electrons

Is that electron-positron (virtual) pair located between the electron and the proton? Since it will get a little crowded when this pair appears between the electron and the proton, what will the proton and the electron do in response to sudden appearance and disappearance of those transient fields - the zwitterbewegung dance?

5. Aug 29, 2004

### colinr

Apparently Heisenberg said that the law of conservation of energy can fail by an amount E, for a time t, provided that E x t < h (planck constant)

So the electron-positron pair can appear out nothing but only last for about 10^-21 seconds. During this time they emit a em wave which travels about 10^-12 metres (I figure thats about 1% of the typical distance between the proton and the electron).

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So when measuring the force between the proton and electron at large distances the force is in keeping with the fine structure constant. But if you measure the force at short distances, the effect of screening caused by the transient pairs is less, so the effective force between the proton and electron appears larger, and is quantified by a number larger than the fine structure constant.

Now I can't even understand what I just wrote because I think there is a gap in my knowledge represented here by ******* if anyone can help fill it in or just to explain some small part, I would really appreciate it.

6. Aug 29, 2004

### Gonzolo

The radiation produced by the pair also has some energy, which must also obey E x t < h. Since radiation energy E is very large (it will spread as a bundle containing all 2*mc2 of the annihilating short-lived pair), t is very small. In such a short t, the travelling distance is very short because c is too slow.

Last edited by a moderator: Aug 29, 2004