# Talk:Static forces and virtual-particle exchange

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Here is a section which was completely wrong

## Contents

### Inverse square law

The virtual-particle picture can be used to provide a heuristic explanation of the inverse square law for gravitational and electrostatic forces. If we imagine that a body emits a virtual particle and that virtual particle is absorbed by another body a distance r away, then the uncertainty principle states that

$\Delta E \Delta t \approx \hbar$

where $\Delta t$ is the time it takes the virtual particle to travel between bodies, and $\Delta E$ is the energy of the virtual particle. If we imagine that $\Delta E$ is a kind of potential energy and we assume the virtual particle travels at the speed of light, then

$\Delta t \approx { r \over c }$

and

$\Delta E \approx { \hbar c \over r }$.

The force is the gradient of the potential energy, therefore

$F \propto { 1 \over r^2 }$,

which yields the inverse square law seen in both electrostatic and gravitational forces.

### Why it's wrong

Virtual particles don't have to travel at the speed of light. If you emit a virtual photon, the virtual state is spread out over all space, and can be absorbed instantaneously. In Feynman perturbation theory, the propagator is nonlocal, and it is the nonlocal part tht gives exchange, not the speed-of-light part.

The other mistake is that this derivation assumes that all virtual particle that are emitted are absorbed, without geometrical dilution. This is also wrong. But the two mistakes cancel each other out. This argument is ridiculous, but it should be left here to prevent other people from putting it in.

## Direction of unit vectors

I wouldn't like to look too nit-picker, but at the beginning of the subject, describing gravitation and electromagnetic force I would have preferred "...having the direction either from M to m or vice-versa..." and "... having the direction from Q to q, or vice-versa...".paolo de magistris 16:03, 21 February 2012 (UTC) — Preceding unsigned comment added by Demaag (talkcontribs)

## To mediate

Please, give an explanation (as in a dictionary) of the verb "to mediate". In absence of such explanation, the subject article is void of any meaning.paolo de magistris 14:32, 20 June 2012 (UTC) — Preceding unsigned comment added by Demaag (talkcontribs)