2) The Quantum Realm
This connection between Doctor Strange and another movie isn’t obvious at first, but when you have it spelled out it becomes clear that it’s another instance of the MCU foreshadowing the introduction of Doctor Strange’s mythology.
In Ant-Man, we learn that when Hank Pym’s shrinking suit gets too small it enters into a subatomic reality known as the Quantum Realm – a place without time or space which is filled with trippy images that would look at home in Doctor Strange.
Kevin Feige has confirmed that’s because the Quantum Realm (which is known as the Microverse in the comics) was intended to give the audience their first taste of the weird and exotic other dimensions that Doctor Strange would properly dive into.
“If you look up the study of quantum mechanics, when you get down that small, as Hank Pym says, space time is meaningless, and there’s a lot of that stuff that applies to Doctor Strange. So this is sort of an appetizer for, ‘If you think this is weird… ‘”