[Spoilers for Ant-Man and Captain America Civil War]
One of my favorite hobbies is retro justifying. Where you apply the logic of a universe to itself in order to justify the impossible and the illogical. This is because I grew up as a star trek fan. And if you don’t “fix” the logic holes your not invested in the Sci part of Sci-fi.
So onto Hank Pym’s pocket tank.
It’s established within universe that once Ant-Man shrinks down that he hits with the force of a full grown man. He has not lost an ounce of weight. That would mean that the tank Hank Pym carries around on a key-chain weighs about 68 tons. Hank Pym still looks in good shape for his age but I doubt he is hitting the gym hard enough to lift that.
Okay so my answer comes in two parts either may be 100% true or one my be false but if the other is true than the proof still holds.
Hank Pym is and has intentionally or mistakenly lied about the properties of his Pym particles
2.) Gravity is a property of the Quantum.
Gravity as a property of the Quantum is the easiest explanation since so little is understood about this fundamental force of the universe.
Hank Pym as a liar is far more likely IMHO. First piece of evidence is that if all his particles did was shrink the distance between particles. All you would need to do is apply the same method Edison used to invent the light-bulb. Which is probably the method that Cross attempts. The result of which is vastly different than the pym particle.
These are the properties of the Pym particle as we observe them in Ant-Man
The Pym particle violates the square-cube law.
The Pym particle and the cross particle both require a structure (suit or container) to operate “safely”.
The Pym particle unlike the cross particle is stable and does not leak or decay.
I think the solution to our tank problem is this. The way in which the Pym and cross particle function is that they do not only shrink the distance between particles but that they do this by constructing a lattice throughout the entire unit being shrunk. This lattice creates false particles and negates real particles. By creating false particles within the lattice Scott Lang doesn’t fly away when he is giant and hit by a breeze. Imagine that the Pym particles also can create a way to negate the properties of real particles. So when you shrink down a tank and have the intention that the tank weighs 68 tons to less than 2 ounces the Pym lattice suspends or negates 67.9999375 tons.
The cross particles are not stable and there lattice begins to decay after it is created. The Pym particles are static but manipulated by the regulator on the suit.
This solution fits the throwing disks as well. Since the throwing disk come in two varieties enlarging and shrinking.
The throwing disk after hitting a solid finds the border between the solid and the surrounding air and commences shrinking or enlarging.
This lattice may also act as a membrane allowing Scott Lang to breathe the same amount of oxygen a normal sized Paul Rudd would need. Very effect for when he is small but when he is large. This membrane would be unable to create enough “false” oxygen to feed his giant brain.
This membrane and lattice would also explain why that ugly dog is able to continue to live. Since the Pym membrane and lattice is stable, does not decay, and continually refreshes itself around the borders of its effected object, That ugly dog would ingest a normal amount of food for a dog but only have access to the amount needed for an ant.
TL;DR Hank Pym is a liar
the Pym particle doesn’t simply change the space between particles.
The Pym particle creates a magical lattice and membrane between the shrunk and the world in order to violate the laws of physics.
If you enjoyed this then you might want to read my take on Ready Player One and how the protagonists for both the movie and book are not the same person but work for their medium.