If you got just one thing from your elementary school science class, it’s the fact that matter comes in three states—solid, liquid, and gas. And maybe you retained the fact that all matter will change states under the right conditions. Water, for example, takes three forms in your kitchen alone: liquid water, ice, and water vapor (steam). Nothing uncommon so far. Class dismissed.
But wait—what about glass? Solid, right? Windowpanes, drinking glasses, and tiny unicorns are all solid stuff that doesn’t go with the flow. But you may have heard that glass is actually a “super-cooled liquid.” A solid theory? Not quite. Glass is, in fact, an intermediate state of matter that your chemistry teacher probably glossed over—an amorphous solid. Informally, the term “super-cooled liquid” could describe the variable states of any kind of matter (like saying that ice is “super-cooled” water). But glass is special, stuck somewhere between liquid and solid. To us, it appears solid in every way, but on the molecular level, it’s not as clearly organized as crystals like table salt or diamond. Kind of like those people who appear to have it all together, but really, they’re in dire need of the Marie Kondo treatment.