downer98

  Alpha particles are two protons and two neutrons emitted 
  by some heavy nuclei, such as uranium-238. Usually these 
  are bound inside the heavy nucleus and would need lots of 
  energy to break the bonds keeping them in place. But, 
  because an alpha particle inside a nucleus has a very 
  well-defined velocity, its position is not so well-
  defined. That means there is a small, but non-zero, chance 
  that the particle could, at some point, find itself 
  outside the nucleus, even though it technically does not 
  have enough energy to escape. When this happens – a 
  process metaphorically known as "quantum tunneling" 
  because the escaping particle has to somehow dig its way 
  through an energy barrier that it cannot leap over – the 
  alpha particle escapes and we see radioactivity.

  The temperatures at the core of the sun are not high 
  enough for the protons to have enough energy to overcome 
  their mutual electric repulsion. But, thanks to the 
  uncertainty principle, they can tunnel their way through 
  the energy barrier.

  These "virtual particles" appear in pairs – an electron 
  and its antimatter pair, the positron, say – for a short 
  while and then annihilate each other. This is well within 
  the laws of quantum physics, as long as the particles only 
  exist fleetingly and disappear when their time is up. 
  Uncertainty, then, is nothing to worry about in quantum 
  physics and, in fact, we wouldn't be here if this 
  principle didn't exist.