Our relation with the universe could be summerized in these words: We get some perceptions from the universe, and they are not random, there are some regularities. Mathematically, this means that our perceptions could be described by an expression smaller than the one describing them in the form in which they appear to us (in the same way that, for example, the expression: "ABCABCABCABCABCABCABCABCABCABC" which contains 30 characters can be described by "ABC repeated 10 times" which contains only 21). This constatation allows us to suppose that our perception is the unfolding of a smaller "germ", which we could call the reality, and to build some mathematical models of this reality. But these models are not the reality itself, they are only mental constructions in our minds. Several models can yeald to identical perceptions. In this case, it makes no sense to ask which is the real one, because they are all real since all are concordant with our perception. For example, it does not mean anything to ask if there really exist other worlds if these worlds are completely inaccessible to us. From this point of view we can also say, for example, that a theory saying that the universe has been created yesterday, or one second ago, with coherent memories put in our brains giving us the impression that we exist since several years, is perfectely real because if it was true, we would perceive exactly what we actually perceive. But, depending on the goal we want to reach by constructing a model of the reality, we might prefer one model between several which accord with our perceptions. I think that almost every physician agrees with the fact that the better model is the simplest one, but the divergence concerns the precise definition of the simplicity of a model. IMHO, the most important is not the complexity of the concepts used by the model, nor the fact that it is far from our immediate perception. I think that a good measurement of the complexity of a model is the number of characters of a text describing it in an adequate language (this point should be precized...). Has anyone another idea for defining the complexity of a model? With this definition, the many worlds theory seems to me to be simpler, because the fact that there are many worlds does not add complexity to the theory if the same physical laws apply to all of them, and we avoid the problem of the collapse of the wave function. I think that in fact the real reason that makes the many worlds theory difficult to admit is that we like to feel ourselves at the center of the world. It has been difficult to admit we live on one planet turning around one star lost among the myriads of other stars of the universes. Many scientists still does not admit easily the fact that our civilization could be only one among millions others, perhaps more advanced... and of course it is much more difficult to admit that our world could be only one among an infinity of possible worlds. However, when I take a decision, I often imagine the different worlds resulting from this decision, their future evolution, and I ask myself which of them I prefer to explore... One could go much further with this idea... How could we explain the fact that the physical laws are just the right to allow the development of complex life ? (the anthropic principle...) Simply because we are here to talk about that! There could exist many other universes whose physical laws does not permit the apparition of complex forms of life, but in these universesw there would be noone to talk about these questions... This yields to a very simple Theory of Everything: "Each mathematical model of a possible universe generates a universe." This theory, whose complexity is only 67, explains completely our universe and all possible universes. Who propose better ? It also answers to the most fundamental metaphysical interrogation: "Why is there something rather nothing ?" Even if there were nothing, mathematics would exist because it can be defined as the studying of the structure of nothing. So mathematical models would exist, then universes would exist. Is there any place for the spirit, consciousness and free will in all of this ? I think it could appear in universes generated not by a finite mathematical model, but by an infinite one, which could be defined as the limit of an infinite sequence of finite models, which approximate the reality more and more precisely but never reach it. The spirit might be the part of the reality which the model does not describe, a part getting smaller and smaller, but never empty, when the model gets more and more precize. "What a small computer can do with a big program, a big computer can do it with a small program. Hence the logical conclusion that an infinitely big program can run alone, i.e. without help of any computer." Stanislas Lem, "Professor A. Donda".