There are major SPOILERS for Avengers: Infinity War below, so read ahead at your own risk. Now that Infinity War has been in theaters for a week, many devoted fans of the Marvel Cinematic Universe have started to speculate about what the ending means and how it sets up the upcoming Avengers 4. There have been some pretty good fan theories that seem to make sense, but a new theory blows them all out of the water. It's just so crazy that it might work in setting up Avengers 4.
Thanos is able to obtain all of the Infinity Stones by the end of Infinity War and snaps his fingers as Thor impales him with the Stormbreaker axe. Nobody knows what exactly is happening and neither does Thanos, who uses the Space Stone to teleport to safety. Meanwhile back in Wakanda, half of the MCU literally turns to dust as Thanos finishes his quest to wipe out half of the universe. Doctor Strange is the only one who has seen the future and knows that Tony Stark will have a large role to play in the eventual takedown of Thanos.
That being said, a new fan theory suggests that Thanos didn't do anything wrong at all. Infinity War screenwriters Stephen McFeely and Christopher Markus have called Thanos' story a hero's journey more than once and they keep telling MCU fans that they won't expect what happens in Avengers 4. This theory suggests that Thanos created a second Big Bang, creating a parallel universe where everybody who turned to dust went. This theory seemingly makes sense when thought about through the words of McFeely and Markus. Plus, Infinity War goes out of its way to mention that the Infinity Stones were created during the Big Bang.
Redditor datageek9 believes that the MCU will go with a future that is dependent on technology because of Doctor Strange saving Tony Stark's life. Additionally, he points out that Ant-Man 2 is the next MCU movie to come out, noting that the Quantum Realm may have something to do with finding the parallel universe where half of the universe resides with the same resources. If true, this would mean that Avengers 4 would center on the Avengers trying to find their way to the rest of their crew, crossing into a new universe. Pictures from the set of the movie highlighted Tony Stark's B.A.R.F. technology, which could be used along with the Quantum Realm.
The theory is pretty out there, but it somehow makes more sense in terms that it isn't as predictable as the other theories that are floating around. It seems that Stephen McFeely and Christopher Markus know about the Soul World theories and the time travel theories, therefore debunking them without specifically addressing them. At the very least, this is the most creative out of the fan theories currently floating around the internet about the end of Infinity War and setting up Avengers 4. You can read the theory in full over at the Fan Theory sub Reddit.