3 ms·

I don't know much about this, so how does the "fabric of spacetime" compare to "field" explanations of action-at-a-distance? e.g. a magnetic field accurately pr

I don't know much about this, so how does the "fabric of spacetime" compare to "field" explanations of action-at-a-distance? e.g. a magnetic field accurately predicts observations, but doesn't actually explain them. Is the fabric is any way more real than a field? (I didn't look to Chomsky for this; that video is just where I happened to first hear this "mechanical" idea explained, and it's still the only place. A better citation would be the sources he cites in the video. My main point was not about modern physics, but the history of science i.e. "mechanical". And, for history of science, an elder respected academic is probably best to look to, anyway. It's hard to think of a specialist in history of science, because by nature it is not a hot, progressive field full of exciting new discoveries, which is what scientists usually get known for. BTW Do have a listen to the start of the lecture, it really is quite interesting.)

Steuard 8y ago
Very belated reply: I don't consider a magnetic field to be an "action at a distance" explanation at all, so I'm not sure how to answer your first question. In classical E&M, a magnetic field is a local property of space at every point. Moving electric charges affect and are affected by the magnetic field at their location in a specific way, and disturbances or changes in that field propagate outward in accordance with a local wave equation. Nothing is ever "action at a distance", because the field itself carries influences and signals from point to point. (I suppose it could look like "action at a distance" if you pretended that the field was just a made-up theoretical construct that wasn't really there. But that's very much contrary to the accepted perspective on fields at least as I understand it. Things like "fields carrying energy density" and "finite-speed propagation of field changes through empty space" seem to argue strongly for taking fields seriously.) So I guess I'd say that the "fabric of spacetime" explanation is on roughly the same footing, though my own intuition feels like the spacetime variant is a bit more concrete, somehow. (I suspect a fair number of people would lean the other way, mind you.) Spacetime is very clearly here and real, and Einstein taught us that its structure is definitely dynamical. Adding a magnetic field is, mathematically, basically arbitrarily stapling a gauge bundle onto that spacetime manifold: it's one step more abstract and arbitrary.

Steuard 8y ago

Very belated reply: I don't consider a magnetic field to be an "action at a distance" explanation at all, so I'm not sure how to answer your first question. In classical E&M, a magnetic field is a local property of space at every point. Moving electric charges affect and are affected by the magnetic field at their location in a specific way, and disturbances or changes in that field propagate outward in accordance with a local wave equation. Nothing is ever "action at a distance", because the field itself carries influences and signals from point to point. (I suppose it could look like "action at a distance" if you pretended that the field was just a made-up theoretical construct that wasn't really there. But that's very much contrary to the accepted perspective on fields at least as I understand it. Things like "fields carrying energy density" and "finite-speed propagation of field changes through empty space" seem to argue strongly for taking fields seriously.) So I guess I'd say that the "fabric of spacetime" explanation is on roughly the same footing, though my own intuition feels like the spacetime variant is a bit more concrete, somehow. (I suspect a fair number of people would lean the other way, mind you.) Spacetime is very clearly here and real, and Einstein taught us that its structure is definitely dynamical. Adding a magnetic field is, mathematically, basically arbitrarily stapling a gauge bundle onto that spacetime manifold: it's one step more abstract and arbitrary.