Sometimes, it may seem that putting your child to bed causes them to have more energy. As if related to the confinement of their bedroom (or bed even). This, of course, is entirely natural behaviour because electrons do it all the time.
Keeping your child from rolling out of the bed using a bed rail is like keeping an electron confined in a potential well.
Electrons, you should know, are classically speaking capable of sitting relatively still in one position. When an electron is trapped in a little piece of material though, and that piece of material is cut into smaller and smaller pieces, then eventually the trapped electron will start to feel quantum confined. The technical term for this situation is ‘particle in a box’. The more that the electron is confined (the smaller the box is), the more it starts moving around. It can no longer sit still as its lowest allowed energy state is non-zero and increases the more you confine the electron, all in line with the Heisenberg uncertainty principle.
Eventually though, your child will be asleep (and if not, a few lines of the above paragraph should knock them out). However, the occasional movement does continue during sleep and with this there is the chance of them falling out of their bed and onto the floor. According to theory, one solution would be an infinite mattress. Practically speaking though, a better solution is to retrofit a bed rail to their bed to minimise the chances of them rolling out. With such a bed rail installed, the child would need to somehow obtain the activation energy to surmount the barrier and drop out onto the floor, which is quite unlikely under normal conditions. And this means that you can get a better sleep too.