Why did German physicist Werner Heisenberg visit his former mentor Niels Bohr in occupied Demark in 1941? The question has possessed scientists, historians, politicians, and one playwright. Michael Frayn’s formally innovative and intellectually stimulating Copenhagen explores this puzzle from every angle: ethical, political, historical and human. An exceptionally interesting play, it deserves the esteem it has enjoyed, and its challenging moral conundrums remain searingly relevant.

Many playwrights address the ethics surrounding science, but Frayn takes one step further, using his considerable understanding of scientific principles as his dramatic model. We cannot pinpoint Heisenberg’s behavior anymore than we can the whereabouts of an electron; we must merely observe its effect on its surrounding, in the knowledge that our observations will corrupt the experiment. This is Heisenberg’s Uncertainty Principle, which Frayn skillfully communicates through theatrical language and form, making it surprisingly comprehensible. Don’t be fooled, this play requires considerable concentration, but is well worth one’s while.

David Grindley’s production has many strengths, but does not quite match the genius of its raw materials. Henry Goodman (Bohr) displays a mastery of the stage, probing the auditorium with hushed tones. He is matched by the earnest intensity of Geoffrey Streatfeild’s Heisenberg. Barbara Flynn brings a pleasing wryness to Bohr’s wife Margrethe, though she and Goodman have an unsettling habit of straining the Uncertainty Principle in terms of dramatic pauses, and all three could reign in some of the gravitas that risks taking Frayn’s most resonant lines into the realms of portentousness. The same is true of Gregory Clarke’s sound design, which contains all the right elements, but doesn’t always set the right tone. All in all, the production gives the impression it would benefit from more playing in.

Most of all though, the play’s intimate intensity is far better suited to the Crucible or its Studio (where Frayn’s and Democracy are playing), than the cavernous Lyceum. In marking out Copenhagen as the potentially transferable ‘star’ of the Frayn Season, Sheffield Theatres have not perhaps served this play as well as it deserves. This said, the production provides a robust, engaging and thought-provoking evening, and is well worth catching during its short run.