Introduction

In this volume honoring John Archibald Wheeler, I would like to take a fresh look at the intersection between two fields to which he devoted much of his research life: general relativity (GR) and quantum mechanics (QM). As evidence of his keen interest in these two subjects, I would cite two examples from my own experience. When I was an undergraduate at Princeton University during the years from 1957 to 1961, he was my adviser. One of his duties was to assign me topics for my junior paper and for my senior thesis. For my junior paper, I was assigned the topic: “Compare the complementarity and the uncertainty principles of quantum mechanics: Which is more fundamental?” For my senior thesis, I was assigned the topic: “How to quantize general relativity?” As Wheeler taught me, more than half of science is devoted to the asking of the right question, while often less than half is devoted to the obtaining of the correct answer, but not always!

In the same spirit, I would like to offer up here some questions concerning conceptual tensions between GR and QM, which hopefully can be answered in the course of time by experiments, with a view towards probing the tension between the concepts of locality in GR and nonlocality in QM. I hope that it would be appropriate and permissible to ask some questions here concerning this tension.