What is an Electron Really?

From ChatGPT

This summary, the result of a little prompt-dialogue between ChatGPT and myself, seems as good an account as any other, and is consistent with Matt Strassler's book, "Waves in an Impossible Sea" .

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In the realm of classical physics, an electron is often conceived as a tiny, negatively charged particle orbiting the nucleus of an atom. However, modern physics, particularly Quantum Field Theory (QFT), offers a radically different perspective.

In QFT, an electron is not a point-like particle but rather a quantum excitation of an underlying entity known as the electron field. This field pervades all of space, and what we perceive as an electron is simply a localized disturbance or excitation within this field. This excitation carries certain properties—such as charge, spin, and mass—that we associate with the electron.

The electron's position is not definite until it is measured. Instead, the electron exists in a superposition of possible states, each corresponding to a different location. This superposition means that the electron doesn’t have a single, well-defined position but rather a range of probabilities (quantum amplitudes really) of being found in various locations.

When we incorporate the Many-Worlds Interpretation (MWI) of quantum mechanics, this notion takes on an even more intriguing aspect. According to the MWI, each possible position of the electron corresponds to a different “world” or branch of reality. 

In one world, the electron might be detected at a particular point, while in another world, it appears somewhere else. These different worlds coexist in a vast multiverse which constitutes reality, and the electron’s delocalization can be understood as it existing in multiple worlds simultaneously, with each world realizing a different outcome of its position. Note that in each specific world, the electron is still an 'excitation of the electron field', a 'wavicle' according to Strassler.

This is a difficult ontology to imagine or believe, but it's the best we can do today.

Quantum Gravity and the double-slit experiment

The backlog of books I wish I had already read continues to grow.

Amazon link

"Fields of Color explains Quantum Field Theory to a lay audience without equations. It shows how this overlooked and misunderstood theory resolves the weirdness of Quantum Mechanics and the paradoxes of Relativity. The third edition contains a new and simple solution to "the most controversial problem in physics today": the measurement problem." .. from the Amazon page.

Note (updated Friday 27th July 18): having now read this book I don't endorse it. It's simplistic, misleading and dumbed-down to the max. The author, who is an experimentalist, seems to believe that fundamental physics is best understood through a bluff, no-nonsense, concrete interpretation which in no important sense violates our everyday intuitions. Hard to reconcile with the maths (Hilbert space vs spacetime) .. the problematic ontology of operator-valued fields .. and so on. I accept that he believes what he says and that his intentions are good.

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This post is about quantum gravity. Marginal Revolution  provided a link to this article: "a good explanation of why a theory of quantum gravity in particular is needed". The points made are not unfamiliar (see this superior post from Backreaction*) but the issue is at least somewhat clear.

 " ...you put a (preferably uncharged) test particle in the middle between the slits to see where the gravitational pull goes. If the gravitational field is quantized, then in half of the cases when the electron goes through the slit, the test particle will move left, in the other half of cases it would move right (it would also destroy the interference pattern). If the gravitational field is classical however, the test particle won’t move because it’s pulled equally to both sides. " (Backreaction).

Note that in the former case there's a measurement leading to a 'collapse of the electron wavefunction'.

Take the seemingly-related question: what is the electric field at a point 'at the screen' of an electron in a state of spatial superposition transiting the two slits? (Of course, we know that the electric field is quantised - the photon is the EM field quantum).

I don't recall this matter ever coming up in the usual QM discussion of the two slit experiment. Those are always concerned solely with the spatial trajectory of the electron itself.

It seems to me that this question can't be addressed within quantum mechanics, which assumes a classical electromagnetic field. Surely one must turn to quantum field theory? (See also this from Physics StackExchange). I don't have any top-level, hand-wavy intuitions about that, though. But the book above by Brooks might help.

Still, in QFT the fields are propagating within a fixed spacetime. When it comes to gravitation we're talking about the dynamic metrical structure of spacetime itself. That theory (quantum gravity) really isn't anchored down at all: the reality underpinning spacetime is utterly unlike the continuum of our naive intuitions.

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* I had never studied the Schrödinger–Newton equation.