Thisness and all that

Debate about the physical meaning of quantum theory is probably more intense today than at any time since the 1930s. For those with some familiarity with the basic equations, Paul Teller has an explanation of what it is all about. His An Interpretive Introduction to Quantum Field Theory (Princeton University Press, $35/£23.50, ISBN 0 691 07408 9) is a philosopher’s view, with some discussion of whether quantum entities possess the property of “thisness” and a caution against believing virtual particles to be real.