Do Atoms Ever Actually Touch Each Other?

Introduction

The question of whether atoms ever “touch” each other is intriguing and requires a nuanced understanding of atomic interactions. To clarify this concept, we must first define what we mean by “touch” at the atomic level, as it can imply different things depending on the context.

Different Meanings of Touch

There are three potential interpretations of “touch” at the atomic scale:

1. Influence: Two objects influence each other.
2. Significant Influence: Two objects influence each other significantly.
3. Exact Location: Two objects reside in the exact same location.

It is essential to note that in the atomic realm, the everyday notion of touch—where solid boundaries exist at the same location—does not apply. Atoms do not have hard boundaries; instead, they are best understood as fuzzy quantum probability clouds filled with electrons.

1. Atoms Always Influence Each Other

If we define “touching” as the idea that two atoms influence each other, then we can say that atoms are always “touching.” This is because atomic wavefunctions, which describe the probability distribution of an atom’s electrons, overlap even when atoms are separated by considerable distances. For instance, two atoms that are a mile apart still have overlapping wavefunctions, albeit the amplitude of this overlap is minuscule.

In principle, the influence of one atom on another can be detected regardless of the distance separating them. However, in practical terms, when atoms are more than a few nanometers apart, their influence diminishes to the point where it can be overshadowed by other nearby atoms.

2. Atoms Touch Significantly When Close Enough

If we take “touching” to mean that two atoms influence each other significantly, then atoms do indeed touch, but only when they are close enough. The definition of “significant” is somewhat subjective, but a common approach is to define a mathematical surface that contains approximately 95% of an atom’s electron mass.

For example, when two hydrogen atoms bond to form a molecule of $H_2$, their centers are separated by about $50$ picometers. This separation can be considered a point of “touching” since it reflects the distance at which the atoms start to form a chemical bond.

3. Atoms Never Reside in the Exact Same Location

If “touching” is interpreted as two atoms residing in the exact same location, then the answer is that atoms never touch in this sense at room temperature. This is largely due to the Pauli exclusion principle, which states that no two fermions (a category that includes electrons) can occupy the same quantum state simultaneously. This principle prevents all the atoms in a solid from collapsing into a single point.

Interestingly, under specific conditions, such as at very low temperatures, certain atoms can be manipulated to exist in the same location, leading to a state known as a Bose-Einstein condensate.

Conclusion

In summary, while atoms do not “touch” in the conventional sense, they do influence each other at various levels of significance depending on their proximity. The concept of touching requires a re-examination of what we mean at the atomic level, where boundaries are not as clearly defined as they are in our macroscopic world. Thus, in every meaningful sense of the word “touch” relevant to atomic interactions, atoms certainly do touch, albeit in a complex and subtle manner.