Philosophy of Physics: A Very Short Introduction (Very Short Introductions)

by David Wallace

The philosopher Daniel Dennett defines philosophy as what we do when we don’t know what questions to ask; when we understand enough to work out what the questions are and can start answering them, a new science buds off from philosophy.

My own assessment is that twenty years ago MOND was a highly plausible rival, but by now the level of contrivance and ad hoc modifications required to fit the data makes it most unlikely to be correct.

This idea of space as a thing separate from matter is called substantivalism by philosophers, and contrasts with relationism, the view that all there is in the world is matter. Substantivalists believe space is a substance, a thing itself over and above the material contents of the world; relationists believe ‘space’ is just a pretty way of talking about the relations that hold between bodies.

In the particular context of quantum mechanics, the problem is this: quantum measurement devices are not black boxes, scattered across the desert by benevolent aliens or deities. They are complicated physical devices, built to interact in complicated ways and relying, themselves, on the principles of quantum mechanics. We cannot understand what a measurement device is or what it is measuring, or even if it is measuring anything at all, unless we understand its workings—in which case we need a way of understanding quantum mechanics in order to do so, and on pain of circularity that ‘way of understanding’ had better not presuppose we know what the measurement devices are.