How intense would a fusion reaction need to be to trigger a chain reaction and engulf the planet?
(Inside Science) -- In "Inside the Third Reich," a memoir by Albert Speer, the former minister of armament of Nazi Germany recalls an exchange he had with the physicist Werner Heisenberg and Adolf Hitler: "Heisenberg had not given any final answer to my question whether a successful nuclear...
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It's not possible, and you can know it's not possible because we are constantly bombarded by high energy cosmic rays consisting of all sorts of 'very fusible' and very fast atoms, many many orders of magnitude higher that what comes out of man made nuclear reactions. So, if it was possible, these would 'spark' such a chain reaction already.
Same goes for making world-destroying black holes at CERN.
The reactivity versus density of potential reactants is so low that it is never, ever going to happen exothermally.
The same applies to the combustion of nitrogen and oxygen. I mean, we do actually have a combustible atmosphere, and at the right temperatures and pressures (inside a working diesel engine, for example!) nitrogen will burn with oxygen. But you know that doesn't happen either, we have lightning storms all the time that do precisely that, generate copious nitrous oxides (you can actually smell them, in fact mostly post-cursor ozone) and those reactions don't release untold hell on Earth.
Our atmosphere protects and nurtures us in a cradle of life. We'd better treat it nicely, eh?
On the subject of lightning and nuclear fusion, there is both theoretical and measurable amounts of neutrons formed in lightning strikes. It is difficult to fully assess if this is from deuterium fusion in the water vapour of the air (you are unlikely to find water vapour carry deuterium at higher altitudes, only at ground level perhaps .. deuterium is isotopically concentrated in sea water and there is little of it in rain) or from spallation of molecule in the air from highly accelerated ion collisions.