Is there a word or slang word that can be used to describe something that is invisible on its own and in numbers it is visible?
For example:
One bacterium is hard to see (invisible to the naked eye) but when there is a huge population of bacteria it can be seen (visible to the naked eye)
I used the concept of bacteria to further my point but I don't necessarily mean microscopic organisms.
Edit:
Another example:
One star is hard to see from a distance but when you look at a galaxy (collection of stars) from the same distance visibility is significantly increased.
The use of the word would be in terms of population.
An individual alone in a population vs a large group in a population.
Best Answer
Following your descriptions, the word "gestalt" (borrowed from German - meaning "greater pattern" or "sum of it's individual parts") would seem to come close in meaning.
The individual components (single stars), being relatively unnoticeable alone, become very noticeable within the gestalt of a galaxy.
The individual components (single bacteria), being relatively unnoticeable alone, become quite visible in a visible gestalt forming bacterial colonies.
https://www.thefreedictionary.com/gestalt