You may have at one point in your life wondered is it possible for you to walk through walls? You may have heard before that if you put your hand on a wall, there's a slight chance of passing through the wall. This theory comes from a concept in physics called quantum tunnelling (Quantum tunneling was first noticed in 1927 by Friedrich Hund). 


To briefly explain what quantum tunnelling is, let's say there's a particle moving towards a potential barrier. And in quantum mechanics, that particle has a probability of being in multiple different positions at once, which we represent with a wave function. So as the particle collides with the barrier, part of the wavefunction can pass through, meaning that there's a slight probability of the particle being on the other side of the barrier, essentially passing through the wall in this scenario. 


What should be understood though, is that the probability of just a single particle passing through a small barrier is very minimal, let alone a whole hand or a whole person. But while the chances are low, lower than the chance of you winning the lottery! But they're never zero, so if you keep trying there is a chance your may walk through a wall.