La maggior parte degli atomi che ci circonda è composta di vuoto. Protoni, neutroni ed elettroni occupano in totale all'incirca un millesimo di miliardesimo del volume dell'atomo. Quindi, with all this space (as much as 99.9999999999%), the interpenetration between the two bodies should be such a thing possible, even if our everyday experience tells us otherwise. But, for once, the experience is right. Here's why.
I need a volunteer. Hey you! Yes, I speak just to you! You seem smart enough, then you will go very well for my little experiment today. Let's start.
First, a hand caressed each other. Yes, you read right. Up, caressed. Well, now scratched. Yes, always help, but go easy: without drawing blood. Excellent! And now, clap your hands. Again. Stronger. End of the first part of the experiment.
Now you have to answer a simple question: when you touched, or better, when you think there was contact between the two hands?
The correct answer is: ever!
Yes, you read that right. Your hands have never touched in the sense that their atoms have never come in contact. No matter what they tell you to your senses. The reality is this: you never touched anyone!
not you trust? Here's the answer: just atoms you can not touch each other (if not inside the particle accelerators) because their outer layer is composed of electrons (more precisely one should speak of electron cloud surrounding the atom). And for the Coulomb force, two electrons will tend to move away, and even if forced, they still maintain a safe distance. In reality what we perceive as a contact only the Coulomb force. A little 'as when trying to reconcile the similar poles of two magnets, one gets the impression that you are in the midst of a ball.
Once it is clear this concept, should also be clear why you can not pass through a wall even atoms are made mostly of empty space: the electron clouds of each atom prevent any contact, let alone the interpenetration.
