There's something rather austere about the semi-circle of tiered seating erected on the stage of the Oxford Playhouse this week for Michael Frayn's award-winning play Copenhagen, which continues until Saturday, writes Helen Peacocke.

Members of the audience using these seats sit like jurors about to declare their verdict on the complex world of scientific principles that playwright presents to us.

On the face of it, Copenhagen sounds pretty dull stuff, just two scientists on opposite sides of the war taking a walk together one day during 1941.

Mr Frayn's aim in writing this play was to explore the true nature of a conversation they shared during that walk, which is why this scene and its many possibilities is re-enacted again and again.

Just what did they speak of? It's a mystery which has puzzled scientists and historians for more than 50 years.

Did they discuss the possibilities of making a bomb? Did one ask the other to defect? Or did Werner Heisenberg, played by Alexander Hanson, simply call on his former mentor Niels Bohr (David Horovitvch) and his wife Margrethe (Anna Carteret) to catch up on old times?

And the most important question of all: why was the conversation so brusquely aborted?

Out of the uncertainty of this meeting -- and the uncertainty principle of physics, first identified by Heisenberg in 1927 -- Mr Frayn, who is best known for comedies likes Noises Off, bombards us with scientific terms and possibilities until we gradually come to see just what might have taken place between the two men.

It is a profound, haunting and particularly powerful play which demands almost as much of its audience as it does its actors - and that's its strength.

One leaves the theatre having absorbed complex ideas and scientific terms that become clearer and clearer as the play progresses.

And what's more it is thoroughly entertaining. You do not need to be a doctor of science to enjoy this play, but you do need an enquiring mind.