I'm currently reading 'Every Thing Must Go: Metaphysics Naturalised', by James Ladyman and Don Ross (with David Spurrett and John Collier), in advance of its publication this June. Here I should declare that the authors are advocates of the same philosophy of science to which I adhere, namely 'structural realism'. I take this to mean that, beyond the empirical (detectable and observable) phenomena, the physical world objectively possesses mathematical structures, and these are the structures which physics is converging towards the identification of. Ladyman et al, however, advocate a much more radical version of structural realism, in which they argue that relational structures are the only things which exist; whilst I hold that there are individual relata, which instantiate the structures, Ladyman et al hold that relata themselves are abstractions from relational structures.
It's a fascinating book, and one to which I may return in the coming weeks. At this point, I would just like to share a fascinating observation made by the authors about the structure of money. When the physical tokens of money are considered, they obey 'classical' statistics: if Bob and Alice both have a pound note each, it makes sense to say that something has changed if they exchange pound notes; each pound note has an individual identity. However, if Bob and Alice both have a pound in respective bank accounts, it makes no sense at all to say that something has changed if those quantities are exchanged. And this is exactly the same as the quantum statistics of electrons: if you have two electrons, and one electron is in state A, and one electron is in state B, numbering the particles, and exchanging which particle has which state, does not change the quantum state of the entire system.