Spider-Man: Far From Home is teasing alternate universes. But there’s a catch.

Fans always knew Spider-Man: Far From Home was going to take place in a post-Avengers: Endgame world. They just didn’t know what exactly that world would look like until, well, Endgame hit theaters — and even then, that movie offered more of an endpoint for this phase of the MCU following the death of Tony Stark, the retirement of Steve Rogers, and Thor’s new adventures with the Guardians of the Galaxy than a hint at how the world changed after the Avengers undid Thanos’s snap.

But this week, we finally got the first glimpse of that post-Endgame Earth in a new clip from Far From Home, featuring Peter Parker (Tom Holland) and Mysterio (Jake Gyllenhaal) talking nerdy about how the MCU’s new reality is just one dimension, timeline, or world that is part of a bigger set of dimensions, timelines, or worlds. In comic-speak, a multiverse exists:

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“There are multiple realities, Peter,” Mysterio tells Parker. “This is Earth-616. I’m from Earth-833. We share identical physical constants.”

For Marvel fans, those numbers, especially “616,” are like sirens. They’re direct references to the comic books that Marvel’s movies are based on, which have their own rich history of parallel universes, altered timelines, and all kinds of reality manipulation hijinks — the kind of stuff that could be clues for where the MCU is going next.

But before we get ahead of ourselves, there’s one villainous catch.

Why the MCU being referred to as “Earth-616” is a big deal

To fully understand the “616” reference requires knowing a couple of basic things about Marvel’s comic book world: Its primary universe is called Earth-616, and there were multiple other universes depicted in separate comic books; the attached number is a way to tell the different dimensions apart.

To use an example from Spider-Man’s comic book lore, the Peter Parker story we’ve grown accustomed to — bitten by a radioactive spider, the death of Uncle Ben and Gwen Stacy — happens in 616. Miles Morales, who becomes Spider-Man when Peter Parker dies, lived in an alternate timeline known as 1610, where many of the same characters exist but have different personalities or powers or moral alignments. A story arc called “Secret Wars” later brought Morales into the main 616 timeline.

In fact, 2018’s fantastic Spider-Man: Into the Spider-Verse was entirely about Morales and the concept of different universes colliding:

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The concept of an alternate timeline also appears in Endgame, when the Hulk talks to the Ancient One and is warned that if the Time Stone is not returned, it will spur a new timeline and new reality.

Marvel’s alternate timelines and universes add context and color to what Gyllenhaal’s Mysterio is saying about the “multiverse,” the concept of all these alternate, but sometimes very similar, universes existing independently of one another.

Essentially, the MCU that we’ve watched over the past 11 years is the main universe — but it isn’t the only one.

And since Mysterio says he’s from a different Earth, his appearance introduces the possibility of other characters from alternate timelines showing up — possibly opening a window for, say, Morales, or even a different version of Thor or Steve Rogers or Tony Stark. It could also possibly be how Marvel will introduce its recently acquired X-Men and Fantastic Four characters.

But Mysterio is an unreliable witness

The big catch with this theory is its source in Far From Home. Mysterio is a classic Spider-Man villain who, in the comic books, is a master of illusion and deception and really cannot be trusted. (Also, his code name is literally a riff on the word “mysterious.”)

Further, the two Spider-Man: Far From Home trailers thus far point to a bait and switch: Mysterio is portrayed as heroic and trustworthy, but there’s something about him that just doesn’t sit right (again, his name is Mysterio). Saying that he’s a hero from another version of Earth adds to that bait.

Still, a multiverse theory (likely triggered by Stark’s snap) would be a fun way to introduce fan-favorite characters into the fold. It’s a cool enough concept that fans may hope Mysterio isn’t lying about it. But that theory could all be a complex ruse from Marvel.

We’ll get to the bottom of this when Far From Home opens on July 2.