In attempting to explain the concept of the fifth dimension, Einstein likened it to an unknown force that can stretch and squeeze and bend the universe. It’s as if the universe is a piece of rubber and the fifth dimension is the force that molds and shapes it. For scientists like Einstein, the fifth dimension is some as yet unknown and unobservable physical force acting on our known world. They hypothesize its existence based on the observable effects from the actions of that force. It’s like gravity. You can’t “see” gravity but you can observe the effects of gravity, hence, you can conclude its existence.