You have to figure the folks at Arena Stage are cursing their timing with Legacy of Light. If you’re going to premiere a comedy that alternates scenes of bed-hopping, apple-chomping, Newtonian-physics-debating, Age-of-Enlightenment figures with modern-day sequences in which their present-day relatives cavort and debate along similar lines, you probably don’t want to position your opening just one week after critics have raved over an exhilarating mounting of Tom Stoppard’s Arcadia.

’T’ain’t fair. But can’t be helped.

Stoppard’s opus, remember, features aristocratic friends of Lord Byron and a precocious teen mathematician who alternate—and eventually share—scenes with dueling present-day literary academics, arguing over everything from the Second Law of Thermodynamics and academic overreaching to grouse hunting and landscaping trends.

Karen Zacarias’ world premiere centers on 18th century literary lights Voltaire (Stephen Schnetzer) and his physicist mistress Emilie du Chatelet (Lise Bruneau), as well as her aristocratic hubby (Michael Russotto) and their precocious 15-year-old daughter (Lindsey Kyler). And they alternate—and eventually share—scenes with present-day astrophysicist Olivia (Carla Harting) and her teacher hubby (Russotto again), as well as a young woman (Kyler again) they’ve choosen as birth mother for the baby Olivia can’t have. Legacy of Light mostly concerns itself with motherhood and gender equality, but Zacarias also finds time to reference the gardens at Versailles, the mysteries of dark matter, and a variety of literary reputations.

In short, we’re traipsing through some awfully familiar theatrical territory in the company of a local dramatist who is clever, resourceful and has clearly done her homework, but who—and I don’t mean this in any way unkindly—should really not have to suffer close comparison with the most brilliant wordsmith currently working in the English-speaking theater. At least not yet.

The storyline of Legacy of Light involves two 42-year-old women some three centuries apart, who have intriguingly paralleled pregnancies. Emilie’s is unwanted and dangerous, the result of an illicit liaison with a sexy young poet (David Covington). Olivia’s is sought-after and surrogated when ovarian cancer makes it impossible for the astrophysicist to be a birth mother.

Zacarias has come to some pointed conclusions about the effects of social and personal attitudes on the choices of her characters. The 18th-century pregnancy spurs Emilie into a burst of scientific creativity, while the 21st-century one effectively stalls Olivia’s work; Kyler evokes markedly different anxieties in women she plays in two eras who risk losing out on the benefits of a Paris education.

Alas, while the play’s outline is sharp, the dialogue with which the playwright has filled in that outline often isn’t. Take a moment in which Emilie’s young lover responds to the arrival of Voltaire in their bedchamber with a furious “I am a member of the King’s court. How dare you burst through a gentlewoman’s chamber.”

Voltaire’s riposte—and remember, this is the most original thinker of his age: “How dare your member burst through my gentlewoman’s court?”

“Enough wit,” Emilie admonishes, but seriously….not by half.

Design elements are capably handled, especially one eye-popping 18th-century gown from costumer Linda Cho, but Molly Smith’s generally frisky staging isn’t always deft. She’s allowed the performers to speechify when the author gets up on her soapbox, and there’s a lot of leaning on punchlines and labored.

Still, credit the director with getting the play up on its feet. And credit Arena with nurturing through extensive workshops a work that traffics in ideas of considerable complexity. What Legacy of Light most needs now—if it’s not to be an evening of clever leaps and flat-footed landings—is lightness.