Read Bishop George Berkeley.
Briefly and thus somewhat inaccurately, He held everything is only ideas in some mind. Modern philosophers also recognize the "other minds" problem. I.e. I cannot be sure there is anyone else like me that has thoughts, feelings and a mind.
Personally, I think there does exist a material universe without any perceiver required (IN CONTRAST TO THE GOOD BISHOP) but this cannot be proved. I especially like Berkeley’s reason for the perceived world to follow natural laws -namely only if they exist can God work miracles as miracles are violations of the natural laws. In Berkeley's POV he was a lesser spirit creation of the mind of a greater spirit, God. Everything was God or the mind of God.