Is everything made of particles, fields or both combined?


EXCERPTS: . . . We have learned that much of our world is made of the various atoms compiled in the periodic table of elements. We have also learned that atoms themselves are built from more fundamental pieces. Today, philosophers who are interested in figuring out what everything is made of look to contemporary physics for answers. But, finding answers in physics is not simply a matter of reading textbooks.

Physicists deftly shift between different pictures of reality as it suits the task at hand. The textbooks are written to teach you how to use the mathematical tools of physics most effectively, not to tell you what things the equations are describing. It takes hard work to distil a story about what’s really happening in nature from the mathematics. This kind of research is considered ‘philosophy of physics’ when done by philosophers and ‘foundations of physics’ when done by physicists....

[...] Walther Ritz thought of this as an interaction directly between the two electrons – each one pushing the other, even though they are not touching. This interaction acts across the gap in space separating the two electrons. It also acts across a gap in time. Being precise, each electron responds to the other’s past behaviour (not its current state).

Einstein, who was averse to such action-at-a-distance, understood this interaction differently. For him, there are more players on the scene than just the particles. There are also fields. Each electron produces an electromagnetic field that extends throughout space. The electrons move away from one another not because they are directly interacting with each other across a gap, but because each one is feeling a force from the other’s field.

Do electrons feel forces from their own electromagnetic fields? Either answer leads to trouble. First, suppose the answer is yes. The electromagnetic field of an electron gets stronger as you get closer to the electron. If you think of the electron as a little ball, each piece of that ball would feel an enormous outward force from the very strong electromagnetic field at its location. It should explode. Henri Poincaré conjectured that there might be some other forces resisting this self-repulsion and holding the electron together – now called ‘Poincaré stresses’. If you think of the electron as point-size, the problem is worse. The field and the force would be infinite at the electron’s location.

If the electron does not interact with itself, how can we explain the energy loss?

So, let us instead suppose that the electron does not feel the field it produces. The problem here is that there is evidence that the electron is aware of its field. Charged particles such as electrons produce electromagnetic waves when they are accelerated. That takes energy. Indeed, we can observe electrons lose energy as they produce these waves. If electrons interact with their own fields, we can correctly calculate the rate at which they lose energy by examining the way these waves interact with the electron as they pass through it. But, if electrons don’t interact with their own fields, then it’s not clear why they would lose any energy at all.

In Ritz’s all-particles no-fields proposal, the electron will not interact with its own field because there is no such field for it to interact with. Each electron feels forces only from other particles. But, if the electron does not interact with itself, how can we explain the energy loss? Whether you believe, like Einstein, that there are both particles and fields, or you believe, like Ritz, that there are only particles, you face a problem of self-interaction.

Ritz and Einstein staked out two sides of a three-sided debate. There is a third option: perhaps there are no particles, just fields. In 1844, Michael Faraday explored this option in an unpublished manuscript and a short published ‘speculation’. One could imagine describing the physics of hard, solid bodies of various shapes and sizes colliding and bouncing off one another. However, when two charged particles (such as electrons) interact by electric attraction or repulsion, they do not actually touch one another. Each just reacts to the other’s electromagnetic field. The sizes and shapes of the particles are thus irrelevant to the interaction, except in so much as they change the fields surrounding the particles. So, Faraday asked: ‘What real reason, then, is there for supposing that there is any such nucleus in a particle of matter?’ That is, why should we think that there is a hard core at the centre of a particle’s electromagnetic field? In modern terms, Faraday has been interpreted as proposing that we eliminate the particles and keep only the electromagnetic fields.... (MORE - details)

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