Which Came First the Particle or the Field?

[Wizardsblade]

I was wondering.. Do charged particles creat fields, do fields create charged particles, perhaps both, or maybe they are considered one in the same (not cause-effect)?

 

[Dr.Brain]

To be precise , particle.

BJ

 

[vanesch]

I was wondering.. Do charged particles creat fields, do fields create charged particles, perhaps both, or maybe they are considered one in the same (not cause-effect)?

It is an interesting issue, in fact. The history of physics can be seen as jumping back and forward between the two views. Let us say that "particle" and "field" are two concepts which take on specific meaning only within a certain paradigm of physics.

In Newtonian physics, there are particles - points in Euclidean space with associated properties (mass, charge...). Fields were initially seen only as "continuum approximations" (like in fluid mechanics) which serve as a help in doing calculations. For instance, in Newtonian physics, there's not really something such as "the gravity field". There is only the mutual interaction at a distance of gravity between two massive particles ; but nobody stops you from mentally assigning a field vector at each point of Euclidean space.
With the Maxwell equations, fields became essential. Initially there has been a struggle to keep the "matter particle" picture of fields (the ether), but Einstein's insights (special relativity) showed us that this is - although not strictly impossible - not a very helpful picture ; we have to accept fields as fundamental things out there.

In quantum theory, the concepts of "fields" and "particles" are actually merged in quantum field theory. You can see fields as "an emerging bookkeeping device" of particles obeying the laws of quantum theory; or you can see particles as particular quantum states of fields. Both turn out to be mathematically identical descriptions.

 

[marlon]

To be precise , particle.
BJ

I hope "to be precise" means "historically" in this context. Mathematically, in the most complete "elementary particle interaction"-models that we have, the field is the fundamental property, not the particle. The particle arises because of fluctuations of this field "when it goes from one configuration to another".

marlon

 

[DaTario]

I would probably say that fields came first. One reason for this is that according to Maxwell equations, fields can exist alone while particles always imply the existence of fields.

Best Regards

DaTario

 

[vanesch]

I hope "to be precise" means "historically" in this context. Mathematically, in the most complete "elementary particle interaction"-models that we have, the field is the fundamental property, not the particle. The particle arises because of fluctuations of this field "when it goes from one configuration to another".
marlon

Well, I used to think that too, but weinberg argues that one can just as well see the quantum field as a bookkeeping device for a many-particle system, so it is not so clear that the field is the "fundamental" concept...

 

[George Jones]

Well, I used to think that too, but weinberg argues that one can just as well see the quantum field as a bookkeeping device for a many-particle system, so it is not so clear that the field is the "fundamental" concept...

But doesn't this only work in inertial frames, i.e., what about the Unruh effect in fllat spacetime and related effects in curved spacetime.

From Quantum Field Theory in Curved spacetime and Black Hole Thermodynamics by Wald:

In the past, much attention has been devoted to the issue of how to generalize the notion of "particles" to curved spacetime. One of the key points which will be emphasized by our presentation here is that this issue irrelevant to the formulation of quantum field theory in curved spacetime - in much the same manner as the issue of how to generalize the definition of global inertial coordinates is irrelevant to the formulation of general relativity. Quantum field theory is a quantum theory of fields, not particles. Although in appropriate circumstances a particle interpretation of the theory may be available, the notion of "particles" plays no fundamental role either in the formulation or the interpretation of the the theory.

From Quantum Fields in Curved Space by Birrell and Davies:

One of the lessons learned from the development of this subject has been the realization that the particle concept does not generally have universal sighificance.

Regards,
George

 

[vanesch]

But doesn't this only work in inertial frames, i.e., what about the Unruh effect in fllat spacetime and related effects in curved spacetime.

Interesting remark, didn't think of that. I wonder how Weinberg views this. He seems to be pushing the "bookkeeping of particles" viewpoint, no ?

 

[robphy]

As a follow up to the passages transcribed by George Jones,
you can find more of these comments by following "Search inside this book" at these Amazon pages: https://www.amazon.com/gp/product/0226870278/?tag=pfamazon01-20 Wald
https://www.amazon.com/gp/product/0521278589/?tag=pfamazon01-20 Birrell and Davies

 

[George Jones]

I wonder how Weinberg views this. He seems to be pushing the "bookkeeping of particles" viewpoint, no ?

It seems so. From the preface of Weinberg's The Quantum Theory of Fields:

The traditional approach, since the first papers of Heisenberg and Pauli on general quantum field theory, has been to take the existence of fields for granted, relying for justification on our experience with electromagnetism, and 'quantize' them ...

The most immediate and certain consequences of relativity and quantum mechanics are the properties of particle states, so here particles come first - they are intorduced in Chapter 2 as ingredients in the representation of the inhomogeneous Lorentz group in the Hilbert space of quantum mechanic.

Hmmm.

Regards,
George

 

[dextercioby]

Quite interesting is the fact that classical fields emerge when putting on $M_{4}$ automorphisms of $\mathbb{C}^{2}$ (and some 3 other spaces, see Wald, General Relativity, chapter 13) seen as the space of an irreducible nonunitary 2-dimensional representation of $SL(2,\mathbb{C})$, which is the universal covering group of the restricted Lorentz group...Quantizing these classical fields in the canonical formalism ------->existence of quantum fields.

Daniel.

 

[George Jones]

see Wald, General Relativity, chapter 13

As I have said before, the finite-dimensional non-untitary representations are useful in that they can be used to construct unitary infinit-dimensioanl representations on Hilbert spaces. This is what Wald does in chpater 13.

Note that Wald s screws up a bit on page 346. I first saw this pointed out by the science fiction writer (and computer programmer and mathematician ...) Greg Egan on sci.physics.research. The relevant thread (in which I also participated) is here.

Regards,
George

 

[marlon]

Well, I used to think that too, but weinberg argues that one can just as well see the quantum field as a bookkeeping device for a many-particle system, so it is not so clear that the field is the "fundamental" concept...

Well, i know this "bookkeeping device stuff" but i don't really like it because this is a concept that is just an interpretation of what's going on. Just look at photons are interpreted within this context. I mean, it's not wrong but one cannot use this concept to defy the fundamental role of (quantum) fields. That's how i look at this issue.

regards
marlon