it probably pops once it gets high enough... xD I've always wondered about that too, I once had a dream that I was in a plane crash 'cause a balloon got in the spinny thing (brain fart, can't remember what it's called :D)
As you go higher up in the air, the air gets thinner. Eventually the balloon will rise to a great enough height that it is no longer lighter than air. And will no longer rise further. Since a balloon has tiny pores in it's surface it will eventually leak out enough helium so it will fall back to the earth again.
With helium it goes up and as far as the wind carries it until it hits something and pops or goes up so high the air pressure makes it pop. No helium it drops and lays on the ground until it either pops or looses all its air.
11 months ago
Last edited at 6:38PM on 1/24/2013
Actually, a helium balloon will rise up over 100.000 feet; 20 miles or so! Eventually the helium will expand so much, it will cause the balloon to burst. The visible sky ends at about 70,000 feet by the way and above that looks like space. There was a video of some scientists attaching a camera to a balloon as it passed the blue, entered the black and hovered around the ozone layer for a while. It eventually fell and got destroyed though.