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Re: [Phys-L] treating force as a vector ... consistently





On Saturday, August 27, 2016 6:45 PM, John Denker <jsd@av8n.com> wrote:

This is why it is a mistake to write a physics book where the title
and the central conceit of the book revolve around the alleged
distinction between "matter" and "interactions".

Is the electromagnetic field "matter"?  The book says no.  
It is not that simple. I doubt a modern physics book would make a blunt statement that EM field is not matter.EM radiation detached from a charge is a form of matter. A photon can be recorded in a detector as other known particles. Sufficiently energetic gamma quanta can produce electron-positron pairs. 
Yet the particle interacts with the field.  Is the particle interacting
with an interaction?  It's a silly question.  It's a silly way to
think about physics.

True.
The modern (post-1924) way of thinking about things is to consider
that particles are real, fields are real, and the difference between
particles and fields is not particularly significant.
Again, it is not that simple. Even with real photons being granted the status of matter, we can say that a photon can detach from the source (e.g., from an emitting atom), but we do not say that an atom can detach from the photon as its source. Theoretically, we can still imagine an exotic process with two high-energetic gamma quanta colliding to produce, say, a Hy atom, so photons can keep their status of matter. But a static Coulomb field can be described only in terms of virtual photons which cannot be directly observed by usual detectors. It is true that electrons, together with their antiparticles, can also be in a virtual state (say, in vacuum fluctuations). But in both cases the word "virtual" is used to emphasize that the corresponding state is not exactly the same as the real-particle state. And in many cases, the modern physics terminology uses the term "electron-positron field" as well. 

Rather than talking about the electromagnetic interaction "between"
two charged particles, the smart modern approach is to say that
the particle over here interacts /locally/ with the electromagnetic
field.  The field then propagates to the other particle over there,
and then interacts /locally/ with that particle.
When I say locally I mean at a single point in spacetime ... as>opposed to any version of "action at a distance". 
 I think, this does not tell the whole story. The described situation is usually visualized as the whole particle being present in the given location, whereas the field being still spread over space. It is only the local change in the field produced by interaction that starts propagating and transferring the corresponding information to other places. We cannot say that the whole field was concentrated at the particle at the moment of interaction. So there is still a big difference between the particle and the field in such description.   

Moses Fayngold,NJIT

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