system
Given the following post, respond as if you're commenting on Reddit:
human
[General science fiction] How science can explain the size/weight increase of characters like hulk/other shape shifter?

Alright, maybe this have been discussed here before, but, it is possible to use science to explain size/weight in characters as hulk/general shape shifter in fiction?

Well, here is my theory, that is my head canon in those cases, but please feel free to complement/call it bullshit.
Well, in most cases of shape shifter in fiction, we don't see just a change in their form, but also in their weight, but following laws of physics, this shouldn't be possible (u can create or destroy matter, only transform). My head canon, is that when they transform, they just start to suck a lot of air, and their body convert the CO2 on it in carbon they can use to create the bulk of their body, where the other atoms needed for a body to work(potassium, iron, all the other minor shit) is just already stored in their body to use when they need. 
So, people of this reddit, u think this is feasible? If not, how the weight increase happen on those character?
gpt
"Matter can neither be created nor destroyed" is actually not true; at the quantum level, matter is popping into existence all the time, and then popping back out of existence just as quickly.

For the most part, this appearance and vanishing is so small and so fast that it doesn't have any practical impact on the universe.

When someone like the Hulk grows in size, however, it's likely that he's using his gamma-based abilities to capture mass at the quantum level, and adding it to his own. And when he reverts to Banner, that mass is just returned to the quantum void as energy.