It sounds like a question a curious kid (or a sleep-deprived college student) might ask: If atoms are mostly empty space, why can’t we just walk through walls? After all, the nucleus and electrons take up only a tiny fraction of an atom’s volume — so technically, both you and the wall are made up of a whole lot of “nothing.”
The answer lies in the weird but wonderful world of quantum physics and electromagnetism. The electrons in your body and the electrons in the wall both carry a negative charge, and as you might remember from school, like charges repel. So, when you try to push your hand into the wall, the electromagnetic force between these clouds of electrons creates a powerful repulsion — much stronger than you might think. In essence, it’s not your hand “touching” the wall; it’s the electric fields of your atoms saying, “Nope, you stay on your side.”
There’s also the Pauli exclusion principle, a quantum rule that forbids two electrons from occupying the same quantum state. It’s nature’s way of enforcing personal space — even at the subatomic level. So, your atoms and the wall’s atoms simply refuse to overlap.
Put simply, walking through walls would mean breaking both electromagnetic laws and quantum mechanics — two of the most fundamental principles holding our universe together. The next time you bump into a door you thought was open, you can at least appreciate that physics itself just saved you from collapsing into quantum chaos.
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