» The limits of explanation
For McGinn, our favoured modes of explanation, typically involving units, and elaborated by combinations and mappings, don't address the question of how the sensation of redness will always be novel to someone who has never had it before.
The same kind of limitation may apply in physics. Look at how hard it is to get your head round quantum theory, or more recent exotica like superstrings. Other developments in physics also weaken the case for reducing everything to one explanation.
And there are disunities of explanation within physics. Although since Newton most explanations have involved particles and forces, there is now a whole new class of explanations for all those phenomena like, say, how many grains will tumble down the sides of a sand pile if you trickle a few more on top. These involve laws that still show, as cosmologist John Barrow puts it, that the world is highly compressible, in the mathematical sense. But they don't really resemble laws like gravitation or electromagnetism.