Why would they assume Janet van Dyne was still alive?
I was going to ask how Janet van Dyne has survived 30 years in the quantum realm without food or water, but I assume there is probably some kind of answer in the special powers she seems to have gained from said realm, which allow her to heal others.
However, there still lies the question of why Hank would assume she was still alive after 30 years. After all, he didn't know anything about her ability to heal and/or survive until after he had gone deep to rescue her. They were all very surprised at the fact that she had gained these powers after they had already gone through the elaborate rescue mission.
So why would they assume that she might still be alive after 30 years?
Best Answer
They didn't assume she might be alive - it was clear in the first movie that Hank (and by extension Hope) believed she was dead (or at least lost forever).
That changed when in Ant-Man, Scott entered the Quantum Realm and then made it back. This pushed Hank and Hope to experiment in trying to create the Quantum Tunnel in order to find out more about it.
On their first attempt the tunnel was only open for a few seconds before it shut down. However during those few seconds, Scott had a "vision" of sorts of Janet playing hide and seek with Hope as a kid, and called Hank to tell him about it.
The nature of the "vision" is what told Hank and Hope that Janet was still alive and they redoubled their efforts to locate her, which of course they did with help from Janet herself, when she effectively broadcast herself through Scott and corrected a few errors in their machine.
On a related note, Janet may not have powers so much as she has absorbed a great deal of "quantum energy" that she can apparently release, as she does for Ava. Bill Foster had suggested that this might be the case and it was how they could try to save Ava/Ghost from the condition that was killing her, by infusing her with Janet's energies.
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How did Janet stay alive in the quantum realm?
When Janet was lost in the Quantum Realm, she was only left with her suit and genius intellect. By the time Hank was finally able to reconnect with her, she had become a survivor in the Realm. She carried a cloak, the mouthpiece from her Wasp mask, and a staff made from her wings.How did Janet van Dyne come back?
When Hank Pym entered the Quantum Realm, he tried to find van Dyne but began to have his mind warped. However, van Dyne was able to find him and used her superhuman abilities she developed while trapped to stable his mind. She then removed her mask, and the two stood before each other, emotional, finally reunited.How did Janet survive without food?
Taking all that into account, Janet could have found a civilization within the Quantum Realm, which provided her of sustenance, somewhere to live, and anything else she might have needed (though some argue that due to her shrinking to a subatomic level, she wouldn't have needed food or anything to survive).Why did Janet van Dyne age endgame?
Maybe Van Dyne spent only 30 (perceived) hours in the quantum realm, but some of the quantum particles sent time through her body thus making her look older. Scott was just too short in there to get his fair share of quantum aging. She didn't perceive only 30 hours. She said "I'm not the same woman I was 30 years ago."Hank pym quantum realm | zombie virus | what if episode 5 clips
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Answer 2
I would like to add some points to the excellent answer by Dave.
Hank believed that the quantum realm was irrelevant of time and space. So he thought that Janet might be alive.
a reality where all concepts of time and space become irrelevant
Of course this was not completely true as Janet aged but it is what he believed. He worked hard to rescue her and gave up. He decided to give it an another try after Scott came back from Quantum realm as pointed out by Dave,
That changed when in Ant-Man, Scott entered the Quantum Realm and then made it back. This pushed Hank and Hope to experiment in trying to create the Quantum Tunnel in order to find out more about it.
Then once Scott had his vision Hank then confirms that Janet is alive.
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