"Upside Down" Flaw?

In the movie Upside Down, a romantic relationship develops between a budding woman and a maturing man respectively living on two planets entangled through two opposing types of gravitational forces. Each world is constructed of material unique to its gravitational force. Matter from each world falls inward torwards its respective planet. The movie describes how matter transported from one world to another eventually combusts. This effect is seen when the more oppressed world's primary heat source for the man's home is shown as combusting material from the other world. This effect is more noticeable when the man travels to the other world using other-worldly matter as weights to sustain him on his partner's planet. And here is where my problem is:

If the man uses matter from the other world to weigh himself down towards the woman's planet, why do the weights combust? They are gravitationally attracted to their planet. He is gravitationally attracted to his planet. He is on the wrong planet - he should be dead!

plot-explanation upside-down

Best Answer

As I understand it, the idea is that when matter from the from one worlds remains in direct contact with matter from the other world for long enough, both eventually start to combust. It's a similar concept to matter and anti-matter annihilation, except it's not immediate.

So, when Adam loads down his jacket with heavy up-world matter, it pulls him towards the up-world, strongly enough to offset his own weight pulling him toward the down-world. But the up-world matter is in direct contact with his down-world jacket. So, after a few hours or so, the material starts to combust, and Adam has to get rid of it.

This is the reason why people from up-world can visit down-world, but they can never really stay there. Eventually, their clothes and probably even their bodies would start to react with the surrounding environment, but they can get away with it for short periods of time.

(I can't remember if they explained how the bees were able to avoid this problem, since they supposedly gather pollen from both worlds, but they appear to be an exception to this rule.)