>>4
There is indeed plenty of supply. I was assuming that humans are interested in maintaining their existence ad infinitum. In such a case, the finite supply would be crippling
eventually. If we're just interested in the short term, of say 1 million yrs, then I don't think supply is an issue.
Deuterium isn't that rare, but tritium is. There isn't enough lithium around (I think?) to get all our tritium that way. Once we figure out how to accomplish fusion without tritium, then that becomes a non issue.
I suppose we could send harvesting missions to Jupiter after we run out of hydrogen here, but getting hydrogen from outside of earth is hardly a trivial task.
I'm pretty sure cold fusion's already disproven. Right now, they're trying to maintain the plasma cloud for as long as possible. The fact that it's OVER 9000K doesn't help. I'm not too concerned about nuclear proliferation, but the hippiefags will, and listening to them will be painful. Not having radioactive fallout is great, as is building reactors in deserts [middle east! lol]. Building in antarctica is a bad idea... reactor detonation = +3m to ocean levels.
Most of the helium found on earth are underground. As for floating in the upper atmosphere... the problem I saw in my thermo book suggested that at equilibrium, a gas in a gravitational field will, on average, be infinitely far away... which makes it surprising there's an atmosphere on earth at all. There's probably something else the question assumed/ignored.