Love and physics in a parallel universe proves a winning formula, says Marianka Swain.

Ever wonder what might have happened if you’d made a different decision? Nick Payne’s ingenious 70-minute play, which has been on tour and to Broadway since its 2012 Royal Court premiere, uses theoretical physics to explore our fascination with the road not taken.

Or rather the road is taken, but it’s one of millions. The basis for Constellations is the quantum multiverse theory, which suggests the different outcomes of every event and decision exist somewhere in a parallel universe.

Payne fractures the romcom, providing multiple variations on each familiar relationship landmark. In one version, cosmologist Marianne (Sherlock’s Louise Brealey) is immediately rebuffed by beekeeper Roland (Joe Armstrong); in another, they engage in hilariously gawky flirtation. Their first date is stiff and self-conscious, sweetly solemn, or – aided by alcohol – frank, funny and erotically charged. A break-up is final, or a mere obstacle, and in a sudden shift into darker territory, they might not actually have control over when the end comes. Predestination defeats free will.

The latter development may frustrate, as it undercuts the consequences of individual choices, and Payne’s non-linear storytelling also makes it tricky to track those consequences. Unlike Sliding Doors, with its comparatively straightforward forking, there are countless possibilities, which doesn’t necessarily reward investment in a particular argument or reunion.

But jittery Brealey and amiable Armstrong do sterling work to ground this dazzling intellectual exercise. Their courtship is engagingly authentic, full of awkward but well-meaning miscommunications and missed connections. When love does blossom, it feels as miraculous as any great scientific discovery, and its loss just as monumental.

Michael Longhurst’s snappy production benefits from Tom Scutt’s simple yet striking set: bare platform, acting as blank slate, and suspended balloons evoking stars, atoms, brain matter or emotions. Imperfect, but astronomical ambition.

Rating: 4/5 stars