The Physicist's Approach to Psi

As a student of physics, one grows up in a climate of optimism. One experi-ences how Nature can be described in terms of mathematically simple laws which the human mind is able to comprehend. In quantum theory one finds an elegant and powerful tool which-one feels-may well be the final theory for all there is to know on this earth, ranging from atoms to living organisms. Quantum theory, apart from its practical success, has raised profound and puzzling questions on the nature of physical reality and the role of the human observer, but these questions have remained on the periphery because they seemed of no practical relevance. Through the results of psi research it became apparent that quantum theory has flaws in a very practical sense. Applied to a systems that include human subjects the predictions of quantum theory were seen to be sometimes incor-rect. This finding may well touch upon the open problems of the role of the ob-server in quantum theory, the nature of reality, and perhaps even on the prob-lem of consciousness. For our present discussion we will put these profound problems aside and look at psi from the view of an optimistic and practical minded physicist. We will consider the psi effects as a challenge to either modify the quantum for-malism or to look for other novel mechanisms. The Causality Principle A most striking feature of psi effects is the violation of the causality princi-ple. Causality, in the meaning in which I am using this term, concerns the time order between cause and effect, with the cause always preceding the effect. From early childhood we get used to the principle of causality. If the milk is spilled, somebody must have tipped the cup, and there is no way to undo the accident by changing the past. Causality has become so much an integral part of our common sense feelings that a non-causal world appears almost unthink-able. And even though theorists with little regard for naive common sense feel