Coulomb forces and Van de Waals forces are phenomena of the nano world that can also be observed under the right conditions in the ordinary-sized world. There are, however, some very strange phenomena that occur only at nano level and cannot be explained by the physical principles of the ordinary-sized world.

The tunnel effect is perhaps the most famous example.

In the quantum world, a particle with kinetic energy that is less than the potential energy of a barrier cannot normally penetrate that barrier. This is why, for example, protons or neutrons are normally incapable of escaping from a nucleus. Under certain conditions, however, particles manage to surmount a higher energy barrier.

For example, heavy atoms like radium and uranium emit radiation, changing into different elements as they do so. If the radiation emitted is alpha rays, this process is known as "alpha disintegration". Normally a force, known as the nuclear force because it operates within the atomic nucleus, prevents alpha rays from escaping the nucleus. In cases of alpha decay, however, the common explanation is that alpha rays escape the nuclear force as a result of the tunnel effect.

In the quantum world, electrons and other elementary particles do not exist in a single, fixed location, but rather occupy a certain area with a certain probability. This means that when a particle hits a barrier, some of its wave energy will escape through the barrier in proportion to its probability. This is known as the tunnel effect.

The tunnel effect is a very difficult phenomenon to grasp, but you may find it easier to picture if you think about it together with the phenomenon of superfluidity described earlier.