‘Stuart Fails to Save the Universe’ Multiverse Science Explained

SPOILER ALERT: This story contains spoilers from the series premiere of “Stuart Fails to Save the Universe,” now streaming on HBO Max.

HBO Max’s “Stuart Fails to Save the Universe” opens in a post-apocalyptic Pasadena, an alternative world where zombie hands poke out of the ground, giant moths terrorize, random tears in reality serve as vacuum portals to unknown parts of the galaxy and survivors barter with their last remaining canned goods.

About the only thing still operating is the comic book shop run by Stuart Bloom (played by Kevin Sussman), where the gang on “The Big Bang Theory” would sometimes hang out. But even that store is no longer normal, as geeky fights among patrons quickly turn deadly. It’s not a great place, so when another Stuart from a different dimension arrives, so begins our main character’s quest to save the universe.

According to Alt Stuart, it was “The Big Bang Theory” characters Leonard, Sheldon and Howard who built a quantum interference device that caused reality to be altered. Regular Stuart and Bert (Brian Posehn) embark on a quest to find the device at Cal Tech — and along the way, reconnect with Denise (Lauren Lapkus) and discover that Kripke (John Ross Bowie) has turned into an evil gang leader controlling much of the San Gabriel Valley. They also find Raj (Kunal Nayyar), who’s been imprisoned by Kripke for quite some time and is looking to help them fix the device.

They’re all captured, but Bert uses his geology expertise to create bombs with rocks and water — and they make it to the device. All is saved, until Kripke kills Raj — and the device then activates, taking Stuart, Bert and Kripke to another universe.

So how much of the show’s multiverse can be explained by science? Sussman credits co-creator Bill Prady with having a handle on where the science works. “There’s a bunch of quantum physics involved in the show, and Bill is an expert on quantum physics theory,” Sussman says. “You can get away with a lot because at the end of the day, it is theory. It’s popular theory, but it’s legit. So I would ask him a question like, ‘how can my character be here and be there at the same time?’ And I had an epiphany at one point when I realized, oh wait, so it’s not just parallel universes — it’s parallel universes with a little time travel mixed in!”

Sussman says there were points while filming the show where it would help to understand the quantum physics theory behind what was happening in a particular scene.

“I look forward to people on Reddit trying to dissect what’s happening because I know that all of it can be argued,” he adds. “I would try to poke holes in it on set, and Bill always walked me through. ‘No, see, the reason why this does make sense is A, B and C.’”

Prady explains that the device that Leonard, Sheldon and Howard built seems to have shifted the primary characters to a universe with a separate, distinct history that has an apocalyptic event that occurs sometime after “The Big Bang Theory” and before we meet them.

“The Einsteinian issue that time is a fourth dimension comes into play here,” he says. “Because when the device malfunctions, it alters reality, but it creates a new past as well. So when we meet them in the first episode, the apocalypse is some years ago, and that’s a result of the alteration. Both the past and present and the future are altered from what they should have been.”

So then the question is, when the characters move between universes, does the universe they left still exist, or is it being restructured?

“That is ambiguous, and they don’t know, and we don’t know,” he says. For example — now that Kripke has killed Raj, that doesn’t seem good right? But in Episode 2, he will point out that either the universe they just left doesn’t exist anymore, in which case he didn’t kill Raj because that Raj never existed, or that they’re we are dealing with an infinite number of universes, and so he just killed one Raj out of an infinite number, which is pretty minor.

But “the branching theory of multiverses states essentially that every quantum event that could go one way also could go the other, and at that point there’s a branch, both universes exist side by side… The theory is that the universe branches at every decision point, so there’s a rapidly growing, infinite number of universes. That gets into the very annoying realization that some infinities are bigger than other infinities, which is mathematically true and conceptually uncomfortable. But it would state that from the point of the Big Bang, the number of infinite parallel universes increases with every moment that the universe ticks by. So that was kind of the science and pseudoscience that sort of lays this out.”

Prady jokingly adds: “How useless is that?”

But it’s a reminder that “Stuart Fails to Save the Universe” may be science-fiction, but it’s still grounded in some ways.

“When I was teaching at USC, and somebody had a project that involved fantasy elements, I’d say, the most important rule in writing fantasy is that the rules you create for your fantasy have to be as real as the laws of physics. They have to be consistent, and they always have to be the same,” he says.

Prady uses “Bewitched” as an example, with its arbitrary rule that only the witch who casts the spell can remove it. “It’s based on nothing, but it keeps every ‘Bewitched’ episode from being three minutes long,” he says. “Because without that rule, Endora would give Darrin donkey ears, and Samantha would remove them, and we’d be done. Now, can your universe be raggedy around the edges? 100%. And that’s ‘Doctor Who.’ The rules are there, but sometimes they don’t quite work out, and the Doctor will explain.”

In the case of multiverses, the parameters of what we think of as the “multiverse” has been cemented in pop culture by Marvel films, “Rick and Morty,” “Dark Matter” and more. “I think the reason that you wind up with multiverses with similar stories is that the notion that multiverses exist mathematically. Things like string theory and stuff touch on that. So you can build off of what has sort of percolated through the general consciousness.”

Prady notes that not all of it makes sense, and he’s proud of the fact that the characters will acknowledge that.

“A guy online did a scientific analysis of what must be happening in this, and where he explains all the various scientific multiverse theories that we are clearly drawing from,” Prady says. “It was thick, thick science. It does state that there’s an infinite number of multiverses. So clearly, we should send that article to HBO Max and say, ‘look, there’s a scientific basis for additional seasons!’”