You’ve definitely heard the word “microscopic” over and over in your life. “Those sand grains are microscopic”, “scratches on my car are microscopic, I am not worried about them”, “the amount of money on my account is microscopic”, etc. But what does it really mean? What is microscopic? Is there anything smaller than that?
The word “microscope” comes from the Greek:mikrós, meaning “small” and, skopéō, meaning “look”. In other words, it is literally a tool used to look at very small objects. There is a huge variety of different microscopes. In fact, you’ve probably looked through several of them in school. An the reason why they are used in the first place actually describes what “microscopic” actually means – you cannot see some things with your naked eye.
When people say “microscopic” they mean that the thing or the event is so small you cannot observe it properly without some sort of aid, such as a microscope. In other words, it is quite a subjective term, used to describe things that are too small for us to see properly. However, don’t think that it is just some sort of a colloquialism – scientists use the term “microscopic scale” all the time.
In physics microscopic scale is somewhere in between macroscopic scale (objects and events are observable by a naked eye) and quantum scale (we’re talking quantum particles here with distances of less than 100 nanometres). And so the microscopic scale objects are measured in micrometre, which is one millionth of a metre.
In thermodynamics, however, the definition of microscopic scale is a little more complicated. Essentially, it described objects and events that are so small we do not measure or directly observe the precise state of a thermodynamic system. Instead we rely on macroscopic scale to make assumptions about the microscopic scale.
Finally, in biology microscopic scale describes objects that are most commonly too small to see but of which some members are large enough to be observed with the eye. For example, you cannot see a single cell, but can observe the tissue that it forms. Or you cannot see the Cladocera, planktonic green algae, but can see some other organisms from the same class.
In short, all objects that are too small for you to see are microscopic, but there is no precise line between microscopic and non-microscopic. For example, a grain of sand may technically not be microscopic, because some of them you can see with a naked eye. However, to make some sort of observations you may need an aid in a form of a magnifying glass of a microscope, which makes it microscopic. This just means that microscopic scale is in the eye of the beholder or something.