To resolve the discrepancy between waves of probability and our commonsense notion of existence, Bohr and Heisenberg assumed that after a measurement is made by an outside observer, the wave function magically “collapses,” and the electron falls into a definitestate—that is, after looking at the tree, we see that it is truly standing. In other words, the process of observation determines the final state of the electron. Observation is vital to existence.
Michio Kaku, Parallel Worlds: A Journey Through Creation, Higher Dimensions, and the Future of the Cosmos
existence, observation, reality