Quantum Tunneling 101

If you take a ball and throw it into the wall, it will of course bounce of the wall. But quantum mechanically a small piece of the balls wave function will “spill” a bit into the wall(the particles position is also uncertain and has a wave function), but it will not be able to pass through totally. This is because it ball has less energy then the wall.

But as said above you can’t know an object properties too a 100%. This is also true for the energy level of balls, here it’s time and accuracy which is traded for each other. If you want to know the balls energy level with a high accuracy you’ll have to examine it under a long time. If you just examine it for a brief period of time the energy level will be less well defined. This means that the balls energy can fluctuate up and down, and that the shorter time span the higher the fluctuations.

So in fact there is a small but existing possibility that the ball will momentarily gain enough energy so that a large part of its wave function spills right through the wall and passes right through it. And here comes the strange part; the ball wont really travel through the wall. Instead it will hit the wall and reappear on the other side, faster then light. Note, that balls have little probability to tunnel through anything since all particles in the ball have to gain energy at the same time. But particles do sometimes, e.g in alpha radiation the protons and neutrons which will form the radiation particle tunnels through the nucleus currently in, in order to escape.

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