What would happen if you isolated a single atom (or molecule) in a vacuum and changed it's temperature till it changed phases. (solid, liquid, gas, plasma)
For example, lets say you isolated a gas molecule, and froze it into a liquid/solid.

If it's just one single molecule/atom with nothing else to interact with, it's not going to act any differently. How would you know it's changed into another state of matter, or does it simply not change states of matter till another atom is present? would 1 other atoms be enough? 2 other atoms? 3? 4? How many does it need? This seems silly to me. What if changes in states/phases of matter were really changes in arrangement of the electron cloud, which only becomes apparent when multiple electron clouds from multiple atoms/molecules interact with each other. Is this a very dumb idea or did I intuitively deduce something everybody already knows??