• Courtesy Of Mark Washburn
• Izzie Steele and Robert David Grant in Constellations

The splendid individual parts make a still greater whole in Northern Stage's entrancing production of Constellations. Every aspect of theater aligns. The ingredients include the connection between two strong performers; a set and lighting that enrich meaning; a blend of comedy and drama; and the script's unique invitation for viewers to experience time in a new way. Director Sarah Elizabeth Wansley has joined all these elements into a bright little galaxy inside a theater.

Playwright Nick Payne summoned these stars in a 2012 play that incorporates the theoretical possibility of multiple universes. Marianne is a physicist specializing in cosmology. She explains the science to her boyfriend, Roland: "Every choice, every decision you've ever made and never made, exists in an unimaginably vast ensemble of parallel universes." Quantum mechanics isn't a gimmick but a gateway, and the play is not weighed down by its ideas but set loose by them. Anything is possible, and linear time gives way to simultaneous alternatives.

Constellations is a love story, each scene one of the typical points of risk in a romance when two people are wondering how to say yes, how to survive betrayal, how to convey what they feel. For all their emotional significance, the moments are mundane: the unanswered text, the extra glass of wine, the chance meeting. What's new is the play's structure, layering multiple versions of the same event to create the feeling of an eternal present and endless possibilities.

Time slips forward and back as the two characters visit and revisit situations that end differently with each replay. The story begins when Roland and Marianne meet at a barbecue. We see several variations on the theme of her first flirtation: He's married; he's dating; he's not yet over a breakup; he's not interested; he's intrigued. And she's coy; she's clumsy; she's brash; she's drunk. And then they click.

The lines repeat; the moods and outcomes change. Wansley underscores the differences by putting the performers in new positions and giving them small actions they can carry out with changing attitudes. At first, it seems like the ultimate rehearsal, as the actors inject different tones into the same words. But it's more than a clever exercise. We start to see possibilities, not performance craft. We enter a multiverse of subtleties as the variations express human essence.

This production uses sound, light, music and set design to reveal the play's themes in other dimensions. Suggesting the infinity of space itself, scenic designer Joey Mendoza's set is three huge walls of latticework, each soaring to the full height of the theater. Simple geometric shapes and subtle patterns appear in the wood. A huge globe that echoes a moon or a planet hangs over the stage. The heights these elements command contrast with a stage area of low-slung platforms. The actors are beautifully tiny, small as subatomic particles, often seated close together in a world that towers above them.

Mary Ellen Stebbins embellishes the atmosphere with lighting design that seems simple but is actually a wealth of delicate variations, all focusing attention on the actors. She uses big external effects, yet they're never showy and seem to arise from the action itself. Set and lighting establish a grand contrast of scale to echo the show's playful dynamic between small choices and enormous consequences.

To amplify the script's theme-and-variations structure, pianist Rose Van Dyne plays live, partially hidden in the latticework. An original composition by Alek Deva combines percussive rhythms that mirror the repetitions in the dialogue with melodic figures that complement the play's emotional sweep. Occasional fierce plucks directly on the piano strings hint at a universe crackling with indifference. Van Dyne's performance is subtly integrated into the action, providing equal parts sound bath and suspense.

As Roland and Marianne, Robert David Grant and Izzie Steele both turn in impressive performances, but the essence of their accomplishment is working together. The rapid tonal shifts, each carved with precision, are a product of two performers connecting. Grant and Steele are married in real life. The characters they play achieve an intimacy that sparkles through both the comedy and the drama of the story.

Their work is almost a dance, in which the characters express themselves through their changing physical distance. Sometimes we see a closeness that conveys being wrapped in a blanket; sometimes a detachment signaling the little ticking fear that makes every romantic admission a risk. The pair can spin from melancholy to humor with a shoe scuffed in indecision or a step quickened.

Grant and Steele show Roland and Marianne listening to each other with a hunger to know everything the other is willing to share. Wansley and the actors emphasize the story's sorrowful side, and a meditative mood prevails. The humor isn't lost, but the story's depth is stressed by an elegant stillness.

Musical repetition is powerful because listeners learn patterns and hear the next phrase with the richness of memory. They're playing along, participating in the music. Constellations gives viewers the same opportunity. One of this production's finest moments is a scene that's played in spoken words and then, slightly changed, in American Sign Language. Memory lets us follow it; the expressiveness of signing lets us feel it.

The play's concept is part of every scene, but the human story is what registers. This multiverse is less about infinity than about sensitivity, and the play subtly tugs viewers to look closely for the small gestures that allow people to express love and face sorrow. Roland the beekeeper wants the same sense of purpose his bees have. Marianne the cosmologist peers at a pitiless universe and wants to hold on to choice. They find what they need in each other, invested in every possibility.