How to find forces that are not yet known?

[Angrboda]

It starts with the basic senses, sight, sound, touch. If an object or force leaves an impression in our perception, we are able to discern that force and refine our understanding of it through observation and experiment. Once we learn to measure the forces that we can sense, we can look for other forces affecting those through measurements. Chaining this way, we can discover more and more forces. But it all starts with the basic senses. If there is a force which doesn't interact with any of these chains of forces, we will never discover it; it will be invisible for all intents and purposes.