What's up with helium balloons?
Helium balloons have puzzled me since I was a small child. I actually have several unanswered questions about them. First, I've never understood the concept of helium becoming "tired" and causing three-day-old balloons to start coming down off the ceiling. This is patently absurd. Helium molecules are lighter than the oxygen and nitrogen molecules. What would cause them to acquire extra mass? Yet balloons do seem to lose their rising power over time, even when tied with a firm knot and without diminishing in size. Even if the plastic had microscopic pores allowing the gas to gradually drain, this would still make the balloon observably smaller. When I was in second grade, my class released balloons with messages attached to see if anyone would find them and write back. We were to release them on a Friday, but due to rain, we had to postpone until the following Monday. My teacher expressed concern that the helium, still compressed in tanks, would lose freshness over the weekend and our balloons might fail to rise when they were filled on Monday. So apparently helium becomes tired even when stored under pressure. (Or maybe my teacher was an idiot.)
I'm also curious and have never encountered an answer as to what typically happens to a balloon after it is released. How high does it reach at its highest point? What causes it to descend? (Tired helium?) At first thought, I would expect the balloon to burst at some point as the outside pressure diminished. After all, if you thoroughly inflate a balloon at the bottom of a swimming pool and release it, it will pop before reaching the surface. But my impression is that balloons released outside eventually make their way back down to earth. Perhaps the plastic of the balloon exerts enough tension to keep the helium compressed even as the air outside becomes less dense until it reaches an altitude where it achieves neutral buoyancy and then just floats around until its helium gets tired. If it weren't for weary helium, the balloon should theoretically stay up there indefinitely (or even just stuck to the ceiling). What about hydrogen? Does it get tired too?
And for a related question, how come balloons attached to the wall with static electricity invariably come unstuck after a few minutes? Surely the electrons don't become tired and lose their negative charge. A more plausible explanation would be that the negative charge is gradually dissipated into the surrounding air. So would they stay up if they were in a vacuum? (Obviously the balloons would have to contain far less air.)
Also related, on Farscape Rigel farts helium whenever he becomes nervous. How is this possible? (Obviously it is, because he does it.) Helium is an element and a noble gas. The atoms don't bind to anything, so they can't be extracted through digestion from food molecules (since they never occur in molecules). Rigel's food and drink may be laced with large quantities of helium. This is not entirely implausible. After all, here on Earth we carbonate soft drinks with carbon dioxide; they may do something similar with helium elsewhere. But Rigel eats the same food as his companions, and you never see them farting helium. The only other possibility is that his digestive system can somehow transmute one element into another. But that would be as implausible as the ability to poop gold bricks.