IN JAMIE PACHINO's play Splitting Infinity, astrophysicist Leigh Sangold decides to revive her career by writing a book that proves the existence of God. As unlikely as that sounds, it was just such a book, written by a real-life physicist, that inspired Pachino to write the play, which opens this weekend at San Jose Rep.

"It's a very odd book. It stuck by me," Pachino recalls. "I thought, 'What in the world would possess this person ... who clearly was from the world of rational thought, to write this book and go promoting it?" From such questions, her character Leigh was born, a 49-year-old Nobel laureate professor in midlife crisis. Involved with her young postdoctoral assistant, Leigh also has some unfinished emotional business with her lifelong friend Rabbi Saul Lieberman.

Pachino acknowledges that finding the right person to play Leigh can be "tricky." Not only does Leigh have to be convincingly brilliant, according to Pachino, but she must be "earthy and sexy and attractive, and she needs to be a bit of a mess."

Taking on the role, Amy Resnick (who recently played a professor battling cancer in TheatreWorks' Third) seems quite enamored with Leigh. "She's afraid to be here on this earth," Resnick muses, "and that's an interesting role to play because clearly you have to be grounded to go out there on the stage, and yet this woman is not on the ground, and that's a challenge."

Resnick studied the work of many astronomers to prepare for the role. "It's a very solitary science; it's you and the telescope and the cosmos." While the play is full of scientific metaphor in language checked for accuracy by the astrophysics department at the University of Rochester, it really boils down to the relationship between Leigh and Saul. After humming along comfortably for a quarter-century, their "friendship" comes up for re-examination under the pressure of Leigh's crisis.

Structurally, Pachino has chosen to show Saul and Leigh at two points in time. In the first, the young couple spend a night in the telescope's observatory; Leigh is at her zenith, a 24-year-old who has just closed in, mathematically, on the moment of the Big Bang. The second timeline occurs over 10 days when Leigh is, as Pachino puts it, "suddenly looking down the barrel at 50 and thinking 'that me is gone unless I do something right now.'"

Both timelines and both sets of characters occupy the stage simultaneously, posing a challenge for director Kirsten Brandt. "The play is constructed in such a way that they bleed together," Brandt explains. "A lot of my job is making sure we're pitching the momentum in a certain way to reach sort of the big payoff at the end." With Saul a committed rabbi and Leigh working out proofs of God, the play can't help but be about faith. And as Leigh looks backward toward the Big Bang the light of which reaches forward to us, it's also about how the past informs the present and vice versa. "The past never goes away," Pachino notes, "it's always in the middle of who you are."

With all this in mind, Brandt decided on an abstract set design. "We kind of came up with this great idea that the set itself was the workings of a telescope. And so everything's a reflection, because inside a telescope is a mirror, a reflector of course. The past is always reflecting in the present and the present is always looking back on the past."

For the actors the set design poses other unique challenges—for example, a rake or sloping floor. Resnick's take on this design suggests that her Leigh may sparkle with humor. "Oh, yeah; there's a rake. We're always putting on some bizarre surface and told to make it look natural. I don't know why. Our chiropractors ask us that with this look in their eye, 'Why, why, why?'"

SPLITTING INFINITY, a San Jose Repertory Theatre production, previews Oct. 15–16, opens Oct. 17 and runs through Nov. 9. Shows are Tuesday at 7:30pm, Wednesday at 11am (Oct. 15 only) and 8pm, Thursday–Friday at 8pm, Saturday at 3 and 8pm and Sunday at 2pm. Tickets are $32–$61. (408.367.7255)

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