Werner Heisenberg isn’t once mentioned in the drama that carries his name, now on the boards at the MTC’s Samuel J. Friedman Theatre … but it isn’t tough to see why playwright Simon Stephens has invoked him.

Like the physicist, whose “uncertainty principle” is a fundamental scientific theory, Stephens is enthralled by the ways events might play out after a random encounter. He begins “Heisenberg” with one such interaction—a woman has come up behind a man at a London tube station and kissed him on the neck, but he’s not who she thinks he is.

What will happen next?

Stage veterans Mary-Louise Parker and Denis Arndt are the skilled interpreters for Stephens’s rich two-hander, a spot-on rumination about joy and sadness, and how either can seep into proceedings where neither may have been anticipated.

Parker is Georgie, an American in her early 40s who confesses to the man she has kissed him thinking he was her dead husband. We find out a scene or so later that there really wasn’t a husband, but there is a teen son, whom Georgie hasn’t heard from in years.

Arndt’s Irish-born Alex is more than 30 years Georgie’s senior. He’s a bachelor whose butcher shop is failing. We learn about the sister Alex lost as a boy, the fiancé who almost was, and his dead parents, all the while more aware that this man’s emotional life seems to have begun and ended a half-century ago.

If ever there were two electrons in need of shaking up, they're Georgie and Alex. “Heisenberg” isn’t a play with dramatic twists and turns—rather, it’s a small, linear story made kaleidoscopic because of two actors with remarkable chemistry.

Parker, the Tony and Emmy Award winner (“Proof,” “Weeds”), is eccentric in speech and elastic on her feet, twirling her hair and twisting her body as she abruptly and awkwardly pursues Alex. With information gleaned from their first encounter, she tracks him down at his empty store: “Do you find me exhausting, but captivating?”

Captivating, certainly. It’s hard to take your eyes off Parker, who allows us to see Georgie as a multidimensional human being, full of quirks, contradictory emotions and not-always-wholesome motives.

As Alex, Arndt is spare and understated—a man aware he’s in the sunset of his life and comfortable with emotions, only so long as he’s entering them in one of the diaries he’s kept for 60 some odd years. His relationship with Georgie spurs a series of decisions about his own future, each made with military efficiency.

Both actors work as their own stagehands. There are rafters for additional seating on stage, leaving only a sliver of real estate for the duo to work. Two simple metal desks on gliders comprise the only scenery.

Stephens wrote the adaptation for “The Curious Incident of the Dog in the Nighttime.” “Heisenberg” has much of the same lucidity and economy of prose of that story. As has been remarked by others, it also calls to mind Nick Payne’s “Constellations,” which took a different tack in presenting the fundamental unpredictability of human interactions.

The 80-minute play, precisely directed by Mark Brokaw (“The Lyons”), arrives on Broadway after a lauded run last year at one of MTC’s smaller stages.

Surely one hallmark of maturity is being wise enough to recognize contentment when it arrives, regardless of appearance. In the play, Georgie and Alex ultimately influence one another’s paths, for the better. Like their relationship, “Heisenberg” is more than the sum of its parts.

“Heisenberg,” through Dec. 11 at MTC’s Samuel J. Friedman Theatre, 261 W. 47th St. Tickets: $70-$150. Call 212-239-6200.

Follow Robert Kahn on Twitter@RobertKahn