[j1z0]

Correct me if I'm wrong but are not hydrogen and helium two of the most abundant elements in the galaxy? If we ever were to let it all float into outer space (if that's even possible) by then couldn't we just harvest it in space? I know that's by no means cost effective with today's technology but we're talking decades before we might actually run out right.

[dredmorbius]

Hydrogen has a high affinity for bonding with other elements. Most notably water (H2O) and in varying ratios, with carbon (hydrocarbons). Both water and hydrocarbons, along with other forms, are heavy enough to not escape from Earth's gravitational pull at a high rate (though some estimates suggest that a large fraction of Earth's original water has been lost to space).

Helium is on of the noble gasses -- they either do not react or react only very reluctantly with other elements.

Combined with helium's low molecular weight, and since gaseous helium is atomic helium, free helium tends to escape into space.

And as Douglas Adams noted: Space is big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the drug store, but that's just peanuts to space.

There's little chance that pure gold could be profitably recovered from space. Let alone helium.