a couple nights ago whilst my presleep thoughts wondered about, i came across a balloon filled with helium. in this thought, i saw the not uncommon sight of it floating up. then i wondered why it went up and not down or some arbitrary direction. i know helium is lighter than our oxygenic atmosphere, so it rises. to explain this, i figured that gravity must pull the heavier substance downward with more force, so the helium struggles to get out of the oxygen, as water poured into vegetable oil sinks. so, as my thoughts progressed, what would happen if there was no gravity? my hypothesis is, if a helium balloon is placed in an oxygen environment that has no gravity, as in space inside a spaceshuttle, it will stay still, not rising or sinking. what further leads me to think this true is the contemplation of which way it would rise, for, without gravity, which way is up? does anyone else agree with this?