Heisenberg’s Uncertainty Principle states that you can’t know both the precise location and the speed or direction of travel of a particle at any one time. As soon as you stop to take a measure of one, you lose a firm grip on the other.

Don’t panic, though. That’s the all theory out of the way. And, luckily, you won’t need to understand it, nor to dust off and brush up that old maths GCSE to enjoy this heartfelt new play from writer Simon Stephens and director Marianne Elliott. The creative duo behind the phenomenally successful stage adaptation of The Curious Incident Of The Dog In The Night Time.

The play follows the unlikely relationship of Alex and Georgie. He (Kenneth Cranham), 75 and never married, is self-contained, habitual and unassuming. Comfortable with his narrow place in life, if not without regrets. She (Anne-Marie Duff), thirty-odd years his junior, wears her exuberant but fragile emotions like a technicolor coat. Constantly in motion with a beguiling but erratic energy (and a joyously foul mouth) she crashes into his life in a chance encounter at a train station.

Anne-Marie Duff and Kenneth Cranham
Anne-Marie Duff and Kenneth Cranham

Watching these two supreme actors search their way around the hazy edges of their burgeoning relationship is never short of entertaining. Cranham imbues Alex with a sense of rigidness, in his formulaic way of life and his highly cultivated sense of self.

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Duff’s Georgie, by comparison, is a constantly shifting proposition. You’re never sure where you are with her, whether she’s inventing stories or lurching between timid insecurity and unabashed forwardness.

There are some lovely moments as each draws the other into uncharted territory. Such as when Alex, after Georgie has torn herself up over her seemingly multiple personalities, assuages her in his belief that there are no such things as personalities. According to him, there are only the appearance of them in the accumulation of our actions, and our actions are free to change. In the process, he frees himself to become someone he didn’t expect.

Bunny Christie’s ‘box of light’ set works wonderfully well. Growing and shrinking around the characters as the boundaries of their lives contort in a constant state of flux.

At the heart of the play is the intriguing suggestion that people, like the core of nature in the theory of subatomic particles, are inherently fuzzy. If you concentrate solely on who and where you are, you’ll lose sight of the direction you’re heading. Conversely, if you’re only ever looking ahead, the beauty of the finer details of life disappear in the blur of perpetual motion.

The theory might say you can’t know where you’re at or where you’re going at the same time, but you’ll know you enjoyed the journey.

Until January 6, Wyndham's Theatre