# Which Came First the Particle or the Field?

1. Jan 3, 2006

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)?

2. Jan 3, 2006

### Dr.Brain

To be precise , particle.

BJ

3. Jan 4, 2006

### vanesch

Staff Emeritus
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.

4. Jan 4, 2006

### marlon

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

5. Jan 22, 2006

### 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

6. Jan 23, 2006

### vanesch

Staff Emeritus
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...

7. Jan 23, 2006

### George Jones

Staff Emeritus
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:

From Quantum Fields in Curved Space by Birrell and Davies:

Regards,
George

8. Jan 24, 2006

### vanesch

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

9. Jan 24, 2006

### robphy

10. Jan 24, 2006

### George Jones

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

Hmmm.

Regards,
George

11. Jan 25, 2006

### 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.

12. Jan 25, 2006

### George Jones

Staff Emeritus
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

Last edited: Jan 25, 2006
13. Jan 25, 2006

### marlon

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