Ordinary fusion doesn't overcome the Coulomb barrier either. In a purely classical sense, fusion wouldn't happen, since the thermal energies are well below the

Ordinary fusion doesn't overcome the Coulomb barrier either. In a purely classical sense, fusion wouldn't happen, since the thermal energies are well below the height of the Coulomb barrier. What happens is that thermal energies get high enough that the nuclei get close enough to have a significant rate of tunneling through the barrier. It's a quantum mechanical effect. There is a nonzero rate of tunneling through the barrier even at room temperature -- just extremely low, far lower than putative cold fusion claims.