Spoilers for Guardians of the Galaxy Vol. 2 ahead.
Guardians of the Galaxy Vol. 2 is altogether rather distanced from the rest of the Marvel Cinematic Universe. The cosmic arm Star-Lord and co. inhabit is already pretty out there and with his sequel James Gunn has been given free reign to steer into that without the need for the usual world-reinforcing. Certain elements of the film will no doubt carry over into Avengers: Infinity War and all five of the post-credits scenes most certainly set up the future, but for all intents and purposes we're dealing with a standalone adventure.
There is, however, one moment that provides a bit more of a tangible link to The Avengers and the rest of the MCU, at least in terms of location. The film opens on Earth in 1980 Missouri, showing a youthful Ego romancing Meredith Quill and planting one of his expansion pods, and we later return in the film's final act when Ego activates that device sending a big blob of CGI rampaging through the nearby town that, if Peter Quill hadn't successfully stopped him, would have turned the whole of our big rock into part of the Living Planet.
That's the sort of thing that we've come to expect The Avengers to deal with over the past decade, and indeed many people were bracing for a surprise cameo from Iron Man or another hero. Of course, that would be very, very unlikely (even without Marvel's web of contracts) if Guardians of the Galaxy Vol. 2 was, like most MCU movies, set at the time of its real-world release. As it currently stands the Avengers are disassembled; Zemo successfully split them in Captain America: Civil War, sending Team Cap underground and leaving Team Tony with an injured War Machine and mentally unstable Vision.
However, Vol. 2 isn't set in 2017 - it's set much earlier, which poses a bit of a problem.
The Plot Hole Explained
Thanks to word from James Gunn and Kevin Feige respectively we know that Guardians of the Galaxy Vol. 2 is set a few months after the original film (to allow for Groot to be a small twig) and four years before Infinity War. This means the film's events have to take place in 2014 (for anyone in doubt, the year tags of both films state this). Which begs the question, why does nobody respond to a Celestial attack?
Chronologically, the 2014 dating puts Vol. 2 between Captain America: The Winter Soldier and Avengers: Age of Ultron. The key events on Earth at this point are the repercussions of the unmasking of Hydra and fall of S.H.I.E.L.D.; the Avengers had re-teamed to hunt down the various Hydra cells and reclaim Loki's staff from Baron Strucker (a mission they're finishing up in their second film). Cap's hunting Bucky, Iron Man's rebuilt his suits set, Thor's on Earth and the whole Initiative is in full swing. An explosion of planet-threatening alien tech should be on their radar. Particularly so given that, while Tony is yet to have the instigating vision that leads to him erroneously making Ultron, he and Banner are still working on an AI system to keep the world safe - he is more than in-touch with the wider global status.
The event seems to go by without mention. There is the possibility the gang checked it out off-screen between films, but the fact such a cataclysmic event wasn't later cited by General Ross when chastising the team and introducing the Sokovia Accords in Civil War (there's no mark on his world map for Missouri) makes that seem unlikely.
And what of Agents of S.H.I.E.L.D.? Even if we can somehow rationalize the Avengers not caring about the backwaters, it's hard to ignore Phil Coulson and co., who exist explicitly to respond to these sort of complaints. Vol. 2 would take place at the start of Season 2, after they've acclimatized to a post-S.H.I.E.L.D. world and just as the characters were becoming acutely aware of the larger Inhuman issue, so something Celestial would definitely pique their interest. Yet nobody bats an eyelid.
In short, shifting the timeline to enable Baby Groot led to Guardians introducing an Earth-based plot element that clashes with the accepted canon. Whoops.
- Guardians of the Galaxy Vol. 2 (2017) release date: May 05, 2017
- Spider-Man: Homecoming (2017) release date: Jul 07, 2017
- Thor: Ragnarok (2017) release date: Nov 03, 2017
- Black Panther (2018) release date: Feb 16, 2018
- Avengers: Infinity War / The Avengers 3 (2018) release date: Apr 27, 2018
- Ant-Man & The Wasp (2018) release date: Jul 06, 2018
- Captain Marvel (2019) release date: Mar 08, 2019
- The Avengers 4 / Untitled Avengers Movie (2019) release date: May 03, 2019