It is with deep regret and great personal disappointment that I am unable to join you today at this new Copenhagen Meeting. With video recordings and an attentive audience I trust that the meeting will be a little less "uncertain" than the original meeting sixty years ago. At the same time, I am delighted at how strikingly Michael Frayn's dramatic presentation captures that meeting and the personalities involved. Indeed, seeing Heisenberg come to life in the play much as I envisioned him gave me a renewed sense of the man. Later, when I met the actor who portrayed Heisenberg in the New York production, I had the distinct feeling that for a moment I had met Heisenberg!

I never met the real Heisenberg. I exchanged a few letters with him while I was writing my dissertation on his early quantum physics, and I intended to visit him as soon as the work was completed. But amidst the confused whirl of typing and exams that fills the last months of one's thesis work I received word from Munich that Professor Heisenberg had died. Perhaps in a way it was for the better that we did not meet, for he is a man who belongs to the ages and it is only from the remains of his life's work that we and the ages hence will have to construct our understanding of this man and his actions during the difficult and challenging years of the past century.

Viewing the play provided me another unique experience: the realization of how greatly drama can add a new and fertile dimension to history by literally bringing the characters and events of the past to life before us. But while enhancing our perception of the past, drama can--and often must--also distort the past in order to succeed in the pursuit of its own aims. Drama, as we know, is not history, nor should it be regarded as such. I am delighted that this drama has brought so many of the important historical issues to the attention of the general public. Yet I am sometimes dismayed to learn that the general public does not always distinguish between historical fact and dramatic fiction.

Michael Frayn is of course well aware of the distinction. Indeed, unlike most playwrights, he has kindly provided an extensive essay for the public that offers an excellent summary of the historical issues raised by the play. The latest version appears as a 37-page Postscript to the published playbook.(1) The opening sentence goes to the heart of the matter: "Where a work of fiction features historical characters and historical events it's reasonable to want to know how much of it is fiction and how much of it is history. So let me make it as clear as I can in regard to this play."

Michael then notes that historical evidence indicates that the main event of the play Heisenberg's meeting with Bohr in Copenhagen in 1941 did occur; that whatever happened during the meeting, Bohr was upset by it afterwards; and that the personalities of his characters were much as portrayed in the play. Heisenberg's letters and the testimony of his friends and colleagues indicate that Frayn's Heisenberg was more or less as Frayn writes: at first eager, direct, and naive, but by 1941 he had become more "difficult, closed, and oversensitive." Life in Germany had taken its toll on the man.

But the real interplay between fact and fiction occurs, not on the plane of externals, but in the realm of Heisenberg's internal intentions, thoughts, and motives during his Copenhagen visit. This is precisely where the direct evidence is weakest or non-existent, and this is precisely the stage on which the play unfolds its greatest dramatic effects. Such effects are achieved by the invention of thoughts and motives selected and explored largely for their dramatic effect. This makes for outstanding and enjoyable drama. My only concern is, as before, that the general public tends to accept these inventions as historically accurate, or at least as highly plausible. Only by consulting Michael's Postscript do viewers learn that, in ascribing thoughts and motives, "this is where I have departed from the established historical record from any possible historical record." Michael then explains his justification, aside from dramatic needs, for resorting to invention. "The great challenge facing the storyteller and the historian alike is to get inside people's heads...to make some informed estimate of their motives and intentions and this is precisely where recorded and recordable history cannot reach." Thus, he declares, "even when all the external evidence has been mastered, the only way into the protagonists' heads is through the imagination. This indeed is the substance of the play."

In other words, when there is no direct evidence for internal thoughts and motives, storytellers are free to imagine any plausible possibility, the results of which are presumably no worse, nor no better, than history itself. This naturally makes for excellent storytelling, but poor history. Historians do have procedures for handling situations such as this. Rather than resorting to the free creation of imagined solutions, historians can resort to what they do best: seeing events and people in historical perspective and placing them within recreated historical contexts.

Of course, no one can get inside anyone else's head, even if they're standing right in front of you. But we do have the advantage of familiarity with the person, which we can gain by observing him acting and reacting in different situations throughout his entire life. Depending upon our diligence, we can achieve fairly good insights into his attitudes, decisions, and personality leading up to and surrounding important historical events. The September 1941 meeting in Copenhagen did not occur in a historical or biographical vacuum. For Heisenberg, we may refer to the rest of his 74-year life, including, most importantly, the 39 years of his life and the eight years of his struggle with the Third Reich that preceded the meeting, and the five years of war and uranium research that surrounded it.

As I have indicated elsewhere, the Copenhagen meeting took place during a unique phase in the European war, and it took place during a crucial phase in the uranium project, when the theoretical possibility of an explosive became real to the scientists for the first time.(2) By 1941 Heisenberg had already confronted and resolved for himself the important questions about his remaining in Germany and working on fission research; this trip was only one of eight trips that he made to occupied countries during the war; and there are a variety of published and unpublished materials from that period that provide important insights into his state of mind. From a close study of his motives, thoughts, and behavior within these broader contexts and during these related events, we can attain a fairly well founded sense of Heisenberg's state of mind when he left for Copenhagen, and what he hoped to achieve during his meeting with Bohr. Of course, we cannot attain absolute certainty, but in the language of wave functions, a sharp maximum in the probability distribution does occur, thereby greatly reducing the range of imagined possibilities. The challenge for the storyteller then becomes to create a successful artistic rendition of these events in which the uncertainty, or Unbestimmtheit, in the situation is greatly reduced. But, then, that would be a wholly different play, and one probably might less enjoyable than Michael's extraordinary "Copenhagen."

NOTES 1. Michael Frayn, "Postscript," in Frayn, Copenhagen (New York: Anchor Books, 1998), pp. 95-132 and here.

2. D. Cassidy,"A Historical Perspective on Copenhagen." Physics Today, 53, no. 7 (July 2000), 28-32, and here.