system
Given the following post, respond as if you're commenting on Reddit:
human
[General Sci-fi] Regarding the physics of "shrinking."

So we just watched the trailer for the new movie "Downsizing" with Matt Damon and it got us thinking. There have been several movies and books and what not dealing with shrinking a human to teeny tiny size. 

How does this affect the way the individual interacts with the physical world? Can they still absorb oxygen from the atmosphere? Aren't their red blood cells now too small to carry the oxygen? If their food stuffs and, from the trailer, booze aren't also shrunk, can they even properly absorb it into their systems? 

I mean, in Interspace, they shrunk his ship with him so presumably all the air molecules in the ship shrank too. What if those tiny molecules get released into the normal size world? If there are tiny sized resources just floating around, wouldn't something start evolving to take advantage of that niche?
gpt
1. They suffocate because they can't absorb enough oxygen to keep their complex bodies running.

2. They freeze to death because small mammals lose heat rapidly, requiring a insanely high metabolism humans aren't made for.

3. The air will become more like a liquid to them, it feels thicker.

4. Every water droplet is a capsule of doom as something that small can't break the surface tension to break out.

5. you would literally be at the bottom of the food chain, insects, small mammals. And everything else would see you as a snack.

So a simple rule is in place when shinking

Don't.