Unraveling the Mystery: Why Can't We Walk Through Walls?

The notion that atoms are composed of 99.99999% empty space, popularized by science communicators and reinforced by cultural references like Harry Potter and The Avengers, prompts a common question: why can't we walk through walls?

Experts explain that the ability to pass through solid objects is not determined by the material's hardness but by the fundamental rules of quantum mechanics. When matter approaches matter, two primary barriers come into play. The first is the electrostatic repulsion between electrons. Although electrons are not orbiting like planets but exist as probability clouds, the negative charge concentrated on the outer regions of atoms repels the electron clouds of approaching objects, similar to how like poles of magnets push each other away.

The second crucial principle is the Pauli exclusion principle, which states that no two identical fermions (like electrons) can occupy the same quantum state simultaneously. This principle further prevents the electron clouds of different atoms from merging or occupying the same space, creating a repulsive force that solidifies the boundaries between objects.

Therefore, despite the vast emptiness within individual atoms, the collective quantum interactions between the electron clouds of trillions of atoms in our bodies and in a wall prevent them from interpenetrating. The "solidness" we perceive is a macroscopic consequence of these microscopic quantum rules.