February 9, 2002 By JAMES GLANZ Niels Bohr, the great Danish physicist, was known to push his scientific debates mercilessly, pursuing at least one colleague to his sickbed to drive home a point. Michael Frayn portrayed him exactly that way in a play about an argument between the dead spirits of Bohr and two others over what happened in a hazily recalled meeting that they had in September 1941 in Copenhagen, which was then occupied by the Nazis. Even a writer of Mr. Frayn's considerable powers, however, could not have taken into account the chance that the unmistakable voice of the real Bohr might be heard from beyond the grave pressing his version of events - demanding a few more lines, as it were - after the play, "Copenhagen," had already finished its award-winning Broadway run and set out on a national tour. Bohr's rogue soliloquy is included in a previously secret series of draft letters released by his family last week. The letters had been written but never sent to Werner Heisenberg, the renowned physicist who led Hitler's atomic bomb program and who went to Copenhagen in 1941 to meet Bohr and his wife, Margrethe, for reasons that have remained murky. The uncertainty over what actually occurred in a conversation between the two physicists as they went for a walk is the central conceit of Mr. Frayn's play, which had a healthy run on Broadway and is about to open in Chicago and Washington. The letters emphatically express a view Bohr puts forward in more restrained tones in the play - namely, that Heisenberg's reasons for making the trip were far from benign, and certainly did not involve moral qualms over his (ultimately failed) program to build the bomb for Hitler. "Bohr in life plainly remained angrier for longer than I made him seem in the play," Mr. Frayn said in an interview yesterday after having read the letters. "In the play he seems to have risen above the anger he felt at the time, and rather to have forgotten the incident until he is reminded about it by Margrethe." "He plainly hadn't forgotten, and he plainly remained extremely angry," Mr. Frayn said. Bohr worked on the letters in the period between 1957 and 1962. Despite the worldwide outpouring of interest in their release, Mr. Frayn said, one thing they almost certainly will not do is change the play itself. Even the historical postscript to the printed version of the play will not require much modification, he said. "When and if we do another edition on the play, I think I will certainly have to record that these letters have been published, and we now have Bohr's direct testimony as to what his feelings were," Mr. Frayn said. At issue - in the real world of history, documents and recollections - is the question of what Heisenberg, who had been Bohr's protégé when they led a revolution in physics in the 1920's, was up to when he traveled to Copenhagen. Thomas Powers, who wrote "Heisenberg's War," the book that inspired Mr. Frayn's play, believes Heisenberg carried moral qualms about atomic weapons with him and was prepared to offer Bohr a deal: German scientists would not build a bomb if their Allied counterparts did not either. Ultimately, Heisenberg sabotaged the German project from within, Mr. Powers argues. Others believe Heisenberg wanted to "do a little espionage," as the historian Richard Rhodes put it, and learn about the Allied effort from Bohr, who fled Denmark in 1943 and worked on the Manhattan Project. Mr. Frayn points out that Bohr's letters confirm certain elements of the meeting that were known from other sources - for example, that Heisenberg made some intensely offensive statements, at least publicly, about the inevitability of a German victory. But when it comes to what Bohr and many others later saw as Heisenberg's roundabout suggestions that he hoped to stop the German project, the letters contradict him. In a draft made the year of Bohr's death, in 1962, Bohr tells Heisenberg it is "quite incomprehensible to me that you should think that you hinted to me that the German physicists would do all they could to prevent such an application of atomic science." That angry sentence, Mr. Frayn said, "appears to be denying some claim made by Heisenberg." But Mr. Frayn says there is no recorded claim by Heisenberg explicit enough to have warranted this rejoinder. So in this view, Bohr, the spirit, is left arguing with the wind. As a play about the uncertainty and unknowability of intentions - especially Heisenberg's intentions - Mr. Frayn's "Copenhagen" is securely walled off from most imaginable documentary developments, including this one. What does seem to be true in the real world of the audience is that many theatergoers, especially those who have not studied the war and are too young to have lived through it, emerge from performances of the play with an impression that Heisenberg has bested Bohr in their otherworldly debate. With the proviso that he cannot be responsible for how others interpret his play, Mr. Frayn said, that impression may simply stem from historical fact. "Heisenberg didn't, in fact, kill anyone with atomic weapons, or indeed any other weapons," Mr. Frayn said. "And Bohr, rightly or wrongly, did actually contribute to the death of many people through the Allied atomic bomb program." Which may - or may not - provide a window into the mind of Mr. Frayn. Copyright 2002 The New York Times Company