Quantum mechanics is hard to understand not only because it involves unfamiliar mathematics, but also because the usual discussion in textbooks about how to relate the mathematics to the real world is incomplete. Supplying the missing link(s) and working out a fully consistent form of quantum theory is the goal of a research program which I initiated in 1984, and which, with major contributions by Roland Omnes, Murray Gell-Mann, and James Hartle, has resulted in what is now called the consistent (or decoherent) history approach to quantum theory. So far as is known at present, this approach is powerful enough to resolve the various quantum paradoxes (Schrodinger's cat, Einstein-Podolsky-Rosen, etc.) without any mysterious action-at-a-distance, and it makes good sense out of quantum measurements. I have written a book Consistent Quantum Theory (Cambridge University Press) which explains the essentials of this approach.

At present my research program is focused on applying consistent history methods and ideas to quantum information theory and quantum computation. Using the principle that quantum measurements, when properly interpreted, reveal a property of the measured system before the measurement took place, C.-S. Niu and I showed that one could greatly simplify the final step in Shor's algorithm for factoring long numbers. We made similar applications to eavesdropping in quantum cryptography. Understanding the significance of density matrices and entangled quantum states, and investigating the noise produced by quantum copying processes, are among the projects currently underway in my research group. We are also looking for (special) relativistic counterparts of some aspects of the consistent history interpretation which at present are best understood for nonrelativistic systems. Other interests include the problem of irreversibility in statistical mechanics, and various issues, such as determinism and free will, at the interface between science and Christian theology.