The premiere of HBO Max’s “Stuart Fails to Save the Universe” sends former “Big Bang Theory” comic-shop owner Stuart Bloom into a post-apocalyptic alternate Pasadena after a quantum device alters reality. Co-creator Bill Prady says the show’s multiverse premise is rooted in legitimate, if still theoretical, quantum physics, allowing the series to combine parallel universes with elements of time travel.

An alternate Stuart says Leonard, Sheldon and Howard created the device, prompting Stuart and Bert to seek it at Caltech alongside Denise and the imprisoned Raj. They confront an evil-gang-leader version of Kripke, reach the device after Bert makes improvised geological bombs, but Raj is killed and the activated machine transports Stuart, Bert and Kripke to another universe. Kevin Sussman said Prady could explain the scientific logic behind scenes and expected viewers to debate the details online.