Avengers 4 Theory: Why Ant-Man Is Key To Time Travel (And Undoing Infinity War)
3. The "Time Travel Devices"
Now, adding Ghost's technology to the new knowledge of the Quantum Realm that Pym and Lang have discovered since Lang's trip there in Ant-Man, it seems we could see the discovery of a viable means to use the Realm to time travel. And taking the improved tech back from Ghost is bound to be the first key step (she'll probably give it up herself when she realises her employer is the real bad guy and she shares an affinity with former corporate thief Lang).
So why does that matter for Avengers 4? Well, because some of the first set shots that were leaked of Avengers 4 seemed to show the Avengers - Ant-Man, Iron Man and a younger Captain America (from the Battle Of New York era) - time travelling. And not only that, but it appeared that that time travel was achieved not using the Time Stone, but with devices worn on the heroes' hands.
Could the circles on Ghost's suit actually be the same technology that we've seen in those Avengers 4 time travel scenes? The fact that Ant-Man's device is built into his suit and not just worn over the top like the others definitely suggests that he's the source of the technology and passes it on to the others.
It's all coming together...