[MUSIC] In the last lecture we have learned that observation does not alter the wave function of a system to be observed. On the contrary, the observation alters the wave function of the observer. And actually, the observation process is the process of recording information about the system into the state of their observer. If after observation the state of the observer is not changed, then there was no observation. Now the question is, where this different copies of observer exists and why they don't see each other. And the possible answer to this question, a good mathematical description of this suggestion, was given by American scientist Hugh Everett III in his PhD thesis in 1957. And this explanation is now called the many verse or multiverse interpretation of quantum mechanics. So, instead of believing that this split state of the observer is some kind of unclear wave function, Hugh Everett suggested to consider to believe that these different copies of observer actually exist. Where, let's see. Let's draw our experiment, [INAUDIBLE] experiment in the space time. So here we have, The axis, which is time, and along this axis there will be all three dimensions of the space. So at some point of time, we have a snapshot of the universe where the emitter fires a photon and in the direction of this double slit screen. And here in this point of time we have many possible different ways of this photon according to Heisenberg's uncertainty principle because of this widening spot of light. And that doesn't play nice as Einstein once said, and instead of choosing which option to implement the integers, he implements them all. So, for every possible way or path of the photon, there is a snapshot in this space-time which implements this path. And Everett, suggest to believe that these snapshots actually exist and can be the producers of further branching. Like this, some of these branches can eventually merge if they have this exact match, which we discussed in the previous lecture, but most of them don't, so we have this anonymous branching in each point of time. Now, if these branches all exist, and they contain this different focus of an observer for example, these different observers can compute because two intelligent observers are more intelligent than one intelligent observer. And the only problem is how to arrange these computation. As we have show many different copies of a computer of computational system, then of course we want to employ it and to solve maybe different tasks of some problem. And to implement these branching, actually implementing these branching is not very hard, so what happens in the universe this point of time. The problem here is how to correct, how to obtain the result of this distributed computation. Because if v, that's v somewhere over here, if we observe the system then we immediately occur at some branch, so we entangle with our measurement tesult with our measurement outcome. We have our record information in ourselves, so our wave function splits and, now, subjectively we observe only one branch of this and our most computer. And this is what all quantum computation is about. First we have to build a highly isolated system. Because if the system is not as isolated, if someone lose inside of this system then the system becomes wider. And the probability of this branching to merge in some particular outcome becomes very low. So we isolate the system, we introduce this branching on some parameter. So the system computes different parts of the task on this branch. And after that, we have somehow make the system to interfere and we want to read the result from the type of this interference. And this is why this quantum computers, or actually I'll call them quantum systems, so hard to model. Imagine if we only have 1000, for example, particles, each branch and for example two directions, then we have these number of possible branches. It's just something like a number with 30 zeros. Imagine someone asks you to emulate these a classical computer. So this is why this quantum computing is so complicated and so effective and so powerful. In the next week we are going to understand mathematically how this branching is implemented actually. And we are going to learn the mathematical model of quantum computer and of quantum data and quantum logarithms. And this lecture is over, so thank you for your attention, and I hope to see you next week.