Do Atoms Ever Touch?

Overall, yes. But there’s more to this question than a simple answer. So let’s break down atoms into two parts and answer this question separately.

Do the Nuclei of Atoms Ever Touch? Yes.

The nuclei in atoms of our everyday lives usually don’t touch each other. Even the nuclei under a 20-story building aren’t in contact. Outside of our daily experiences, nuclei definitely can touch. In particle colliders, physicists throw atoms at each other to make their nuclei smash together. In space, immense forces cause atoms to squeeze together until their cores touch. But enough about the nuclei, what about the electrons in atoms — do they ever touch?

Do the Electrons of Atoms Ever Touch? No.

Here’s the thing: we have to consider the quantum characteristics of electrons. This means that they act as both waves and particles. Wave-like electrons are spread out over space and oscillate over time, so their location is often described by an electron cloud. This electron cloud represents the density of probability of finding an electron if you were to measure its position. It’s not that the electron is buzzing around within this cloud, it’s actually smeared out in space.

Quantum particles don’t have a defined position, but exist as cloud of probability of being found in a location.

These electron clouds have seven different characteristics that define how they can exist — we call these types of particles fermions. Think of these characteristics as seven digits to their “address” in the universe. Three of these digits make up where it physically resides in 3-D position space. The next three describe the electron cloud’s momentum in each spatial dimension. The last component represents the electron cloud’s spin. No two fermions can exist with the same unique seven-term address.

This property can lead to some pretty interesting situations. For example, we can have two identical electron clouds but differ only in their spin component. This means they can exist at the same point in the universe as long as they have different spin. This property is analogous to how ghosts in movies can pass through walls. These ghosts have a similar spatial location in our world, but they exist in some after-life dimension. This allows them to occupy the same space as physical objects and thus pass through walls, etc.

If the wall was made of only spin-up fermions, a spin-down fermion could pass right through just like this ghost

This, of course, is made up movie stuff, but fermions are not. So even though electrons can exist in the same physical location in space, they can’t have the same seven digit address. Therefore, they never touch. The philosophical reason why fermions exhibit this property is still an ongoing challenge even though it is perfectly predicated and described by mathematics.

All images were produced by me and are free to use however you’d like, but some credit would be nice. Code is found here.