# Tunneling

## Tunneling (Encyclopedia of Science)

Tunneling is a phenomenon in which a tiny particle penetrates an energy barrier that it could not, according to the classical laws of science, pass across. One way of describing this process, also known as the tunnel effect, is shown in Figure 1. Notice that the y-axis in this graph represents energy, while the x-axis represents position. The graph shows that in order for the particle to move from left to right, it must surmount an "energy barrier." In other words, the particle must absorb enough energy to climb over the barrier.

An everyday example of this phenomenon is rolling a ball over a small hill. Suppose you stand on one side of the hill and want to roll the ball to a friend on the other side of the hill. You can do so only if you roll the ball hard enough for it to climb up your side of the hill. If you

Figure 1. A particle before and after tunneling. It approaches from the left with far less energy than it would need to pass over the energy barrier. (Reproduced by permission of The Gale Group.)

don't push the ball with enough force, it goes only part way up the hill and then rolls back down to you.

The tunnel effect would mean in this example that you might...

(The entire section is 863 words.)