MCU Theory: The Tesseract Is Still The Key To The Multiverse

Warning: This article contains spoilers for What If...? episode 1.

The Marvel Cinematic Universe appears to have made the Infinity Stones irrelevant in Phase 4 - but the first episode of Marvel's What If...? teases the Tesseract may still be the key to the Multiverse. The Infinity Stones lay at the heart of Marvel's first three phases, with the Mad Titan pursuing them in order to achieve his insane ambition of rebalancing the universe.

Loki appeared to suggest the Infinity Stones are unimportant to the future of the MCU. That series starred a variant of the trickster god who created a branching timeline by stealing the Tesseract in 2012, and he was taken and put on trial by the Time Variance Authority. To Loki's shock, he discovered Infinity Stones do not work in the TVA - because they possessed an entire drawer full of them, with some of their agents even using them as paperweights. This matches up with the comics, where each Infinity Stone only possesses power in its own universe.

But What If...? episode 1 surprised viewers by bringing back the Tesseract, and even revealing it possesses more power than anyone thought. And the Tesseract's new abilities may well be the key to the entire Multiverse.

The Tesseract Can Be Used To Travel In Time

The first episode of Marvel's What If...? was set in an alternate timeline where Peggy Carter was the one who was transformed into a super-soldier rather than Steve Rogers. In this timeline, the SSR stole the Tesseract from Hydra before Arnim Zola could begin his experiments with it. When Hydra did regain it, they attempted to use its power in a very different way to the main MCU timeline - to open a portal that summoned a monstrous creature from another dimension. Captain Carter sacrificed herself to force this beast back into its portal.

She emerged 70 years later. It seems the Tesseract can create portals through time as well as space, which actually makes sense; according to Einstein's General Theory of Relativity, space and time are closely bound together. If you open a wormhole through space, in theory it can affect time too. It's an amusing retcon of the Tesseract's powers, and it's hard not to conclude the Tesseract can basically do whatever the latest plot demands - including even giving Captain Marvel her super-powers.

The Tesseract's Time Travel Opens Up Major Possibilities

The MCU's Captain Carter is pretty much an original character, but her story is strikingly similar to another alternate version of Captain America's in the comics; Samantha Wilson, the Captain America of Spider-Gwen's reality. In this timeline, Samantha Wilson fought her way to the Vita-Ray chamber when Nazis attacked Project: Rebirth, and underwent the super-soldier procedure. Like Captain Carter, she found herself plunged into an interdimensional gateway. Importantly, though, the comics specified the portal she dove into wove through the Multiverse itself. This raises the curious question of whether the Tesseract could be used to travel through the Multiverse.

In the comics, an Infinity Stone only has power when it is in its native universe. The Avengers learned this in the build-up to Jonathan Hickman's Secret Wars event, when they attempted to use the power of the Infinity Gauntlet to prevent two universes colliding; although they were successful, the breach of the natural order resulted in the destruction of the Infinity Stones. Loki's experience in the TVA would appear to suggest the same principles apply in the MCU - but that isn't necessarily the case, simply because of the MCU's model of temporal mechanics.

How The Tesseract Could Allow Travel Between The Multiverses

According to Loki, the Multiverse naturally skews towards chaos. Any moment has the potential to create branching timelines; they can be formed by a dramatic action, such as the beginning of a war that should not have happened, or just by someone being late for work. Any point where the timeline branches out is called a "nexus," and - given the mundanity of some potential nexus points - there should already be an infinitude of different timelines. Crucially, because some branches were created by minor events, the differences between timelines won't always be dramatic.

This has significant implications for the Infinity Stones. At what point does a timeline diverge sufficiently for the Infinity Stones from its sister timeline to lose all power? Or is it rather a matter of degree - that the further the divergence, the weaker the Infinity Stones, until the differences become so great they lose all power? In either scenario, it's entirely possible the Space Stone's wormholes can travel throughout the Multiverse. While this wouldn't matter for the main MCU timeline, where Thanos destroyed the Infinity Stones, there will be countless other timelines - including Captain Carter's - where the Tesseract still exists.

Captain Carter Could Become A Multiversal Hero

Captain Carter with Sword of Might in What If

The first episode of Marvel's What If...? featured a voice-over from the Watcher, essentially the "Voice of God" in the series, in which he did not claim Captain Carter was just the hero of her world. "Her one choice gave birth to a whole new history," the Watcher observed, "and gave the Multiverse a new hero." This fits with trailers, which have suggested Captain Carter will be a central member of an alliance of Multiversal heroes who oppose some cosmic threat - a team described by Marvel merchandise as the "Guardians of the Multiverse."

Until now, the general assumption has been that the Watcher himself will be the one who forms the Guardians of the Multiverse, abandoning his vow of non-interference and assembling a team of champions. But What If...? episode 1 has just established another possible way to travel the Multiverse, one tied to a member of the team no less. Captain Carter's version of SHIELD has possessed the Tesseract for far longer, and have clearly unlocked its secrets to the extent they can open dimensional portals with it; if the Tesseract does indeed have the power to open wormholes through the Multiverse itself, the scientists of this timeline would be highly likely to discover it. Thus Captain Carter could well become exactly what the Watcher teased, the Multiverse's new hero, and a returning character in Marvel's What If...?

More: What If…? Episode 1: 5 Big Questions About Captain Carter's MCU

Marvel's What If...? releases new episodes Wednesdays on Disney+.