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Re: [Phys-L] long-range forces, short-range couplings



On Monday, July 27, 2015 6:04 PM, John Denker <jsd@av8n.com> wrote:



"How can you have a "long-range" force at all, given that special relativity
and basic notions of causality require everything to be local in space and time?"

I have never met such a requirement explicitly formulated in any known formulation of SR. On the contrary, one of the basic concepts of SR such as distance (or proper length) is non-local in space. Proper time of a process (e.g., a lifetime of an unstable particle) is non-local in time.

"As a corollary, it is madness to try to classify things
as "objects" versus "interactions".  In an electroscope,
you have electrons interacting via exchange of photons.
The size of atoms is determined by interactions that
involve the exchange of electrons.  And when photons
pass near the sun, they interact with it via gravity.
So what's the object in one scenario is the interaction
in another."
The black box model with an intermediate particle hidden in the box explains nicely the repulsive forces. But it does not give similarly straightforward explanation for attraction. How will you use this model to explain the electrical attraction between the plates of a charged capacitor? Or between an electron and atomic nucleus? Or exclusively attractive gravitation force between any two masses? The model with momentum exchange between an object and an intermediate virtual particle carrying interaction forces works fine for conceptual explaining the repulsive forces, but it has always been a mystery to me why it is considered as universal for all interactions in the quantum field theory. It could, in principle, be extended to describe attraction as well, but only with additional and rather superficial assumptions like introducing some dominating paths in the path integral or assuming our Universe to be closed, which is just wrong as far as we know today.  

"Meanwhile, the size of atomsis determined by another process that involves the exchange ofelectrons".

What objects exchange the electron in an isolated Hy atom? And how would this alleged exchange determine the known atomic size? Actually, even though it may sound strange, the size of an object is determined by the  quantum-mechanical indeterminacy (see, e.g., our book "Quantum Mechanics and Quantum Information", Sec. 3.6).

Moses Fayngold,NJIT
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