What can happen when two people meet? The possibilities are endless, but every relationship winds up following a single path, better known as “what actually happened.” But what about all of those alternative possibilities, the relationship roads not taken, the places the relationship might have gone?

We see some of those alternative realities in Nick Payne’s 2012 play, Constellations, now in its Broadway debut at the Samuel J. Friedman Theatre. Relativity, quantum mechanics and string theory are involved in this story — both in the play’s underpinnings and in the words spoken onstage by actors Jake Gyllenhaal and Ruth Wilson. So there are stars of several kinds in Constellations; New York Times theater critic Charles Isherwood tells us if they shine brightly enough for Broadway.