The theory of (not quite) everything : a novel / Kara Gnodde.

Enhanced descriptions from Syndetics:

With the offbeat charm of The Rosie Project and generous warmth of The One Hundred Years of Lenni and Margot, a wry, moving debut novel about a pair of unforgettable siblings and a love triangle of sorts--one with math as its beating heart.

One of Cosmopolitan's Best Books of 2023

Meet Art and Mimi Brotherton. Devoted siblings and housemates, they're bound together by the tragic death of their parents. Mathematical genius Art relies on logic, while Mimi prefers to follow her heart.

When Mimi decides she needs more from life than dutifully tending to her brilliant brother, she asks for his help to find love. Art agrees, but on one condition: that she find her soulmate using a strict mathematical principle. Things seem promising, until Mimi meets Frank: a romantic, spontaneous stargazer who's also a mathematician. Despite Mimi's obvious affection for the quirky Frank, Art is wary of him from their very first encounter.

As Art's mistrust of Frank grows, so do Mimi's feelings, and the siblings' relationship is brought to a breaking point. Something about Frank doesn't quite add up, and only Art can see it . . .

The Theory of (Not Quite) Everything is a tender, intelligent and uplifting novel about brothers and sisters, true love in all its forms, and how the answers to life's biggest questions follow a logic of their own.

Reviews provided by Syndetics

Publishers Weekly Review

Gnodde examines the blurry lines of unconditional love between siblings in her spirited debut. Mimi and Art Brotherton have lived together since their parents died by suicide 12 years earlier. The arrangement is not without sacrifice: Mimi, 30, feels burdened by taking care of Art, 40, a mathematical genius who is dedicated to deciphering an unsolvable problem. Mimi wants to find love, but Art is protective of her and insists that if she starts dating, she must use a website called Matrix, because he approves of its "elegant algorithm and an intrinsic mathematical logic." Contrary to Art's plan, though, Mimi meets Frank, another mathematician, outside of the app. Sparks fly instantly, and Art feels threatened by Frank's presence and worries Frank will steal his work. By the third act, Mimi learns secrets Frank kept about his past, Art is hurt in a car accident, and Mimi wonders if Art was right about Frank after all. Gnodde takes a while to get going, but once the narrative picks up, it really gets to the heart of Mimi's quest for the truth about the people in her life. Readers will be rewarded for sticking around. Agent: Charlotte Seymour, Johnson & Alcock. (Feb.)

Booklist Review

Sorrow, warmth, and tension mix in this unique and compelling novel. Since the tragic deaths of their parents when they were teenagers, siblings Mimi and Arthur Brotherton have been living together in London. Now middle aged, they've developed a symbiotic relationship that makes it difficult for them to break out of their ruts. Arthur, an analytical mathematician, chooses his path based on algorithms and facts. His life's purpose is to solve an equation that could destroy the whole world if proven true. But Mimi follows her gut, which tells her to accept a new job as a sound artist while pursuing a romantic relationship. When Mimi falls for another mathematician, Arthur is dismayed that she hasn't followed his rules, and her new love causes a rift in their structured lives. Arthur believes Mimi's boyfriend is not what he seems, and his dogged pursuit of the facts leads him to devastating injury. With Arthur incapacitated, Mimi must face the truth of both their past and future. Gnodde's debut explores the less examined dynamics of sibling closeness, especially when pushed to its limits.