The central program of science is to abstract the observer from the observed. This is Empiricism, the idea that there is an objective physical reality that we can agree upon and describe in a common language if we discipline ourselves to make observations in a specified, standard manner.
Quantum mechanics has pulled the foundation from under the scientific program. When QM first crystallized in the minds of Bohr, Heisenberg, Dirac and Schrödinger, 1925-27, the talk was about uncertainty and questions that are meaningless because they cannot be asked with an experiment. Heisenberg in particular grounded the Uncertainty Principle in the practical limits of how much you unavoidably disturb a particle with the very light that you need to see it.
But 40 years later, John S. Bell tightened the paradox by demonstrating with a bit of math that there can be no objective reality independent of the observer. The stunning conclusion of Bell's Theorem is that objectivity is illusory. Reality is always co-created by the observer and the observed.
John Wheeler (Feynman's PhD adviser) analogized the situation as a game of 20 Questions where the experimenter is asking the yes/no questions and Nature is answering them, always in a self-consistent way, but without an object selected ahead of time. The first few answers are not about any object in particular, but as more and more questions are answered, the answers gradually bring an object into focus. The final description that emerges has been created half by nature's answers and half by the experimenter's choice of questions.
This is a story of physics research, pursued on its own terms by luminaries in the field, pointing to the inference that the physical description of our world cannot be complete without the addition of observers. Consciousness complements and helps to define physical reality.
Science, pursued doggedly with its own rules and methods, has produced a result that has undermined the most basic of those rules and methods. This paradox is so far from our experience and our culture -- the scientific culture most especially -- that fifty years after Bell, we are still at a loss what to make of it. For the most part, we are ignoring it. One great mystery is why science works so well, why there is so much that humans can agree on, in spite of the fact that objective reality is but half the story, and our subjective choices -- presumed to be individual -- are the other full half.