# Action at a distance

1. Jun 1, 2005

### somy

Hi all.
I want to know what do they mean by "action at distance". I know the concept of field(!!!) and the meaning of "space geometry effects". I wanted to know something about the history of this concept.
Thank you.
Somy

2. Jun 1, 2005

Action at a distance is a problem that Newton recognised with his Theory of Gravity. Simply speaking, how does one mass 'know' that another is near it, and so feel the force? How does the moon 'know' that the Earth is where it is? The same goes for electromagnetic forces.

To get round this problem, the concept of the ether was invented - a substance through with the forces could travel. When this was shown to be wrong in the late 1800s, the idea of a Field came about. However, this didn't solve the problem, it just gave it a name!

We know know about exchange particles that can solve the problem for Eletromagnetic, strong and weak nuclear forces, but for Gravity, there is still a problem, albeit with several proposed solutions.

Last edited: Jun 1, 2005
3. Jun 1, 2005

### Juan R.

I think that Einstein GR does not solve the problem of gravitation. In fact one is substituting the old query

"How does the moon 'know' that the Earth is where it is?"

by modern one

How does the moon 'know' that the curvature of spacetime is where it is?

In the same form that Newton equation just compute force and don't answer the mechanism for it. Einstein field equations just compute spacetime curvature (if any) and don't answer the mechanism for it.

Regarding the supposed success explaining of electromagentic force by means of interchange of particles, one may be highly eskeptic.

- The explaining reliy on many asumptions and unobserved facts (virtual particles are newer seen)

- The explaining only work for asymptotic states for free particles. There is not convincing explaining for bounded states.

- The asumption of interchange of particles is inspired in classical EM field theory with retarded LW potentials. It is known that LW retarded potentials are not good enough, by this reason Feynman looked for the use of advanced potentials also.

Action at a distance is more convincing than field theory.