Why did he come? The mystery behind German physicist Werner Heisenberg’s 1941 visit to Copenhagen to his former mentor, the Danish physicist Niels Bohr, continues to resonate more than 60 years after their meeting. The discoveries in theoretical physics that both Nobel Prize winners had made earlier led directly to the development of the atomic bomb. Heisenberg was head of the German team at work on the practical uses of atomic fission; Bohr lived in a country occupied by the Germans but was on the Allied side. When you consider the implications of Heisenberg’s trip and the impact of the two men’s investigations on the future of mankind (think Hiroshima and the possibility that Hitler might have had the bomb first), it’s no wonder that their private conversation remains a subject of inquiry.

British playwright Michael Frayn has spun the known facts about the 1941 meeting and the canon of scientific articles and biographies into the fascinating drama Copenhagen, which won the Evening Standard Award in London and then Tony Awards for Best Play and Best Director following its 2000 Broadway premiere. The national-touring company of Copenhagen, which is also directed by Tony winner Michael Blakemore, begins a two-week run at the Colonial Theatre this week.

Len Cariou, who won a Tony as the original Sweeney Todd, leads the three-person cast in the role of Bohr, with Hank Stratton as Heisenberg and Mariette Hartley as Bohr’s wife, Margrethe. Over the phone from Philadelphia (the company’s pre-Boston stop), he elucidates. " Why did Heisenberg come? He does say in the play, ‘I couldn’t say specifically why I was there.’ All he wanted to know: was it morally okay to deal with nuclear fission in terms of building a weapon? He says in the play, ‘If I could build a reactor, I could build bombs.’ That’s why he came to Copenhagen. The English had started their terror bombing; they were leveling Germany. They needed some kind of weapon. "

But there are other possibilities. Did Heisenberg want to find out whether the Allies were working on the bomb? Did he tell Bohr that he would not give Hitler the weapon if the Allies stopped their research? Even though both men gave accounts of the event after the war had ended, inconsistencies remain. A newly found letter from Bohr to Heisenberg that was never mailed disputes the German scientist’s version of what happened.

In Blakemore’s production, Copenhagen is set within a huge arena that’s empty except for several chairs. Some members of the audience are seated at the rear of the stage so that viewers out front can see the action mirrored in their expressions and body postures. As a veteran of many Shakespeare productions, Cariou has no trouble performing on a bare stage. " Most of Shakespeare is done that way. It’s great exercise for an actor, a mental challenge because these guys’ minds go at such a clip. "

The play takes place over several decades, combining past and present. Memories of the pivotal moments in 1941 are filtered through the perceptions of the three persons. During the 1920s, when Heisenberg worked under Bohr in Denmark, he had become almost a member of Bohr’s family, and he spent a great deal of time with Margrethe and the couple’s children. Her character functions as the observer, clarifying the two men’s regard for each other. " The relationship that they had — really father and son, " Cariou observes. " Then the war breaks out and they are enemies. Margrethe is saying to Bohr, ‘Look out, this is hostile.’ And I’m saying, ‘No, no, no, this is my son, a member of my family.’  "

Cariou emphasizes that he has no background in science. He began his preparation for Copenhagen by gathering a shelf’s worth of books on the men and their theories. " Unfortunately the stuff is written in science-speak. I found that it was getting in my way. Frayn gives you all the information you need. He’s done a brilliant job in that regard. The play was a beast to learn. Nobody we know talks like that. We had to create a new computer chip for the head for this one.

" It’s not your ordinary play. The way the characters act and interact, they seem to speak so that the other characters don’t hear them. Then you pick up on the dialogue of the one character that it seems you shouldn’t have heard. It makes it difficult for an audience. They have to pay attention. I always say when I’m talking to people, ‘Don’t have a martini before you come.’  "

Broadway in Boston presents Copenhagen at the Colonial Theatre May 7 through 19. Tickets are $25 to $65; call Ticketmaster at (617) 931-2787.