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| 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.
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" ...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.
