At the end of Infinity War, Thanos completes his mission and wipes out half of the universe. Before turning to dust, Nick Fury uses a pager to contact Captain Marvel. A new theory now suggests that pager may have been used to contact Carol Danvers in the past, insinuating that she exists in a separate timeline from the current Marvel Cinematic Universe. We know that the Quantum Realm will play a big part in Avengers: Endgame, so could Fury have used a Quantum pager to contact Danvers?
The Captain Marvel Prelude comic revealed that Nick Fury liked to think of Carol Danvers as his silver bullet, or last resort. Danvers is reportedly the most powerful hero in the MCU, which is something that Fury does not take lightly and the reason why he waited to get into contact with her. As far as Danvers surviving Thanos' snap, she might not have been in the same timeline for that to happen. Why else would Fury be so confident about using that pager to send a distress call? He had to have known that she was still alive and not suffering the same fate as half of the universe.
If Captain Marvel lives in another timeline, that pager may have been made with Kree alien technology back in the 1990s, which would be highly advanced for the time and even for current time. It has already been confirmed that the Quantum Realm from Ant-Man and the Wasp will somehow connect to Carol Danvers, but we don't know how yet. It's entirely possible that she has been using the mysterious dimension to fight evil throughout time, preventing future disasters, which would be the perfect reasoning as to why Nick Fury only uses her as a last resort. Danvers might be fighting in the past to keep everything as safe as she can in the future, or perhaps even traveling to the future to protect the past.
Obviously, this is just a theory at this point, but it sure does help to make sense of Nick Fury's decision at the end of Infinity War. Captain Marvel hits theaters before Avengers: Endgame, so we should have a better idea of how Carol Danvers will be involved in possibly reversing the effects of the Mad Titan's ultimate goal. However, it will more than likely just be a tease, giving fans some more to speculate about before Endgame hits theaters the following month.
If this Quantum pager theory proves to be true, we could see Captain Marvel and Ant-Man sharing some intel about traveling through the Quantum Realm and utilizing time vortexes. Marvel Studios is keeping everything under wraps, but fans were able to correctly guess the Avengers: Endgame title before the studio announced it and they never acknowledged that it was out there, which could be the same thing with some of these fan theories as well. As usual, we'll just have to sit back and be patient. This Avengers: Endgame theory originated from Nerdist.