So, to summarize: if you look at the past, we find nowhere any contradiction with causality, with cause and effect relation. But - here comes Heisenberg's contribution - in regard to the future, it's different. We never can know enough about the present to predict the future, in every case, except for predicting probabilities. Let me repeat the usual form in which this is set. I have a particle, I know it's here now. I want to know where it will be in a second. For that purpose, I have to know the place of the particle and the position of the particle. And Heisenberg points out that in the formalism of quantum mechanics, because of the particle's behavior, in some cases as a wave, you cannot do- know both the position and the momentum or the velocity, at the same time. Now, I want to talk about this in a little detail. Because the idea has not been as generally accepted. I already mentioned that Einstein was not happy about it. Two of my Hungarian friends have not been either. Wigner objects to Heisenberg's reasoning, because Heisenberg says- In order to have enough knowledge about the future, I have an observer, the observer disturbs the state, and that gives rise to difficulties of quantum mechanics. Wigner says- That is no explanation, because I don't know what an observer is. An observer, I am an observer. I don't know myself. Having explained something you don't understand by something else that you don't understand, is not a great feat. I had the same discussion - Eugene would not listen to my answer - I had the same discussion with Johnny von Neumann. And he listened to my answer, and I am glad to say, he agreed with me. And to explain this, I'd better tell you the sharpest objection that has been made to the uncertainty principle, that is connected with the name of the physicist who made the first good Wave Function, good description of the hydrogen atom, Schrödinger. And the story is famous and known as the story of Schröding- Schrödinger's cat. We have the following arrangement. Here we have a radioactive substance that emits, on the average, a particle - an alpha particle - once every second on the average. Now, here I have a counter, and I close that counter, so it won't count, except that I open it for half a second. If, in that half a second, a particle arrives - the probability is one half - then the same apparatus that I have already used can be coupled into other apparatus that will open a horrible door, which will let out some poison, which will kill the cat. So, the quantum mechanical description is, a velo- a probability distribution, after an hour, with the cat, the probability of cat being alive, one half, being dead, one half. And the correct description is that I don't know. Now, here comes our observer, and looks. And his looking will either result in killing the cat for good, or for reviving it. And this finishes, Schrödinger, I can't believe. This is an ob- an objection published, generally quoted, my scientific listeners will know that this is age old and not forgotten, very well known. I have no objection to any of this except that I say- I don't need to look.