OK. Say there is a large brick wall in your front yard. Say you have a baseball and you throw it at that brick wall. It will bounce off. This is because it simply doesn't have enough kinetic energy to plow through the brick wall. A wrecking ball would though. The wrecking ball would simply bash through the wall. Now, the situations these particles are in is very similar to the baseball and the brick wall. Imagine that, when you throw your baseball at the brick wall, instead of bouncing off the wall, it goes through it! Theres not a hole in the wall, but inexplicably, your baseball is on the other side. This is quantum tunneling. These particles, or your baeball, somehow borrow energy from nearby particles or locations and use that energy to jump from one side of the wall to the other, insantaneously, without seeming to go through the space in between. The thicker the wall, the more energy the particles, or your baseball, needs to borrow from other places to go the distance through it. Without that necessary amount of energy, it simply bounces off. This effect is what we're talking about. So far we have no way to control it, but we know that it happens.