In Avengers: Endgame, after

Loki makes off with the Tesseract in 2014,

Tony Stark says to Steve Rogers that he knows

when they were both there, and you know why I know

Referring to Hank Pym and Howard Stark.

Then the two of them

travel back to 1970 to obtain the Tesseract and more Pym particles from Howard Stark and Hank Pym, respectively.

What was Tony referring to when he said this to Steve?

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    Reading between the lines (and perhaps there was an inter-movie comic that explained this) but Steve Rogers discovered the Shield / Hydra facility in New Jersey in The Winter Soldier. Perhaps discussions with Tony revealed that Howard and Hank had worked there when Tony was a child. They also know that Howard had found the Tesseract after the war. Where else might he have taken it? – iandotkelly Apr 30 '19 at 16:51
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    Tony doesn’t say “you know why I know” to Captain America. He says “I know for a fact they were there, and I know how I know.” – David Jameson Aug 3 '19 at 12:35

The problem they have is that they have only one more Pym Capsule each, so if they went back in time to get the Tesseract again, they wouldn't have the Pym to get back to 2023.

Tony says that a stroll down the memory lane brings up "Military installation, Garden State.". It's a time and place that his father, Howard Stark, was working in the same facility as Hank Pym. It's at a time well before Hank quit S.H.I.E.L.D.

Tony says he has a vague idea. It's a bit of a guess which is why he asks Cap if he trusts him. So Tony's guess of the year 1970 is based on the place where his dad worked when he was born and a time when Hank may have fully figured the Pym Particle.

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    Sure, that makes sense but what I don’t understand is why Tony was being vague and insistent on saying “you know why I know” to Cap – Zip Zap J May 5 '19 at 15:05
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    I believe it's for the same reason of work that Howard was doing which resulted in his execution by Bucky. Cap and Steve fought over that in Civil War and they barely patched up. He didn't want that argument to stir up again. – MovieMe May 5 '19 at 19:15

I'm currently watching Endgame on Disney Plus with the subtitles on. Tony and the script both say: "and I know why I know." Not "you know why I know."

I think @MovieMe is right though in his second post. Tony knows to go somewhere around 1970 due to the information about his parents and Bucky revealed to him in Civil War. And he is definitely conveying that through the tone and inflection in his voice. That's why Captain America takes him seriously and knows he'll get it right.


The answer to how Tony Knew how he Knew to go to Lehigh on 4/7/70 is a simple two word answer....STARK EXPO..which Tony viewed video of Expo buildings and Camp Lehigh and read notes and diagrams on during the events of his "house arrest" by Nick Fury during the events of Iron Man 2 this is why Tony says "and i know how i know".Recall Tony listened to his Father Howard say in the video " unlimited energy "and " no more Tedious work (Refereing to the Tesseract( Unlimited Energy) and Pym Particle tedious work( large objects made small to move with ease).both Hank and Howard were at the camp at the same time working on presentations to present at the Stark Expo of 1970 under the protection of the military in plain sight to not arouse suspicion and work in secrecy .

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