Abstract

A different thing is meant by `time’ in QM and GR. This gets in the way of being able to combine the two theories into a coherent whole—the problem of time. I will consider Kuchar’s and Isham’s reviews on this from around 14 years ago. These consider for canonical GR in traditional `metric variables’ 10 conceptual strategies in three families 1) time before quantization, 2) time after quantization, 3) no time at all, and how none of these quite works upon detailed examination. I will make some naive philosophical comments about these, and will then discuss how the picture has changed somewhat since (but the problem of time has certainly not been resolved). That involves the growth of histories theory, the addition of more timeless approaches and how some of the strategies may combine rather than being distinct strands of thought.