When you look around yourself at the world, what you see are solid things that seem to be inhabiting empty space. Most of us think our body is solid. Yet every second there is water flowing through our bloodstream, air is moving in and out, into and through our lungs, our heart beats and sends a vibration of sound through our flesh and bones.
Everything in the universe is energy in different forms.
Humans understand the world around them through their senses - the usual “five” are sight, hearing, taste, touch and smell. The sixth sense is associated with psychic or paranormal sensory perception. Basically, if we can’t sense it with one of the five senses, then it just doesn’t exist for many people.