Why does fusion reactions do not occur naturally on earth but do in the sun?

Answer 1

The conditions at the sun's core give very high pressure due to the gravitational forces, and also a high enough temperature. The earth isn't big enough to produce these conditions, and in any case is mostly made of heavy materials which would not undergo fusion. Efforts to make fusion on earth are using the two materials deuterium and tritium which have the lowest threshold conditions for fusion to start, but even so it is necessary to achieve higher temperatures than even on the sun to make a feasible power plant. In fact fusion on the sun has a surprisingly low power density, and a plant operating at those conditions would have to be huge to produce any useful power. Nothing achieved yet on earth has produced more power output than the input, but development continues and hopefully a solution will eventually be found. If not, mankind will run out of power (but not in our lifetimes).

Answer 2

Because Earth is a planet not a star like the sun. Fusion reactions can only occur naturally in stars

The answer is primarily because of gravity, the sun has so much more gravity than the earth, it's ridiculous, at such high amounts of gravity and heat (caused by said gravity) as is found in the center of a star: fusion will naturally occur, but on earth we can't reach those temperatures or force hydrogen molecules to collide at those speeds in said temperatures for much longer than a few seconds at best.

Answer 3

No, it requires very high temperatures and can only happen naturally in stars

Answer 4

Pressure and temperature.