I've been told that, according to QM, when Hydrogen atoms are left together there is a non-zero probability that they spontaneously fuse (I accept this bit). I've been told further that, because of huge amount of Hydrogen atoms present in the Sun, a substantial proportion of the Sun's energy is released due to this phenomenon - is this true?
EDIT: On second thoughts, this question may be unclear. I think I would answer myself that the conditions of the sun make fusion more probable than elsewhere, so it happens with much greater frequency.
What I was meaning to ask was, with a small amount of hydrogen (neglecting the reduced gravitational effect) would we have to apply a greater pressure and heat in order to produce fusion than with a much, much greater amount - since the greater amount has the benefit of the higher probability of some of the atoms spontaneously fusing anyway?
http://www.youtube.com/watch?v=gS1dpowPlE8&feature=BFa&list=ECED25F943F8D6081C in this video there is a claim made regarding quantum tunnelling in the sun, can someone please explain this phenomenon to me in more detail and tell me whether the video is correct?