All of these choices follow from the same string theory. According to the latest developments in string theory, we may have about 10 500 (or more) choices of the possible state of the world surrounding us. Recent developments in string theory, which is the most popular (though extremely complicated) candidate for the role of the theory of everything, reveal an even broader spectrum of possible but incomprehensible universes. We can enjoy life in a flat or nearly flat universe, but this requires fine-tuning of initial conditions at the moment of the Big Bang with an incredible accuracy of about 10 -60. Nobody would be able to live and comprehend the universe in either of these two cases. A typical open universe would grow so fast that formation of galaxies would be impossible, and our body would be instantly torn apart. A typical closed universe created in the hot Big Bang would collapse in about 10 -43 seconds, in a state with the Planck density. There are three basic types of universes: closed, open and flat. If the huge density example looks a bit extreme, rest assured that it is not. The universe is incomprehensible for anybody living there, and the laws of mathematics cannot be efficiently used. All records about the previous events become erased, so one cannot remember anything and predict the future. All clocks are destroyed faster than one could measure time.
This happens faster than one could measure distance. Quantum fluctuations of space-time in this regime are so large that all rulers are rapidly bending and shrinking in an unpredictable way. Here is the first one: Suppose the universe is in a state with the Planck density r ~ 10 94 g/cm 3. To understand the issue, consider some examples of an incomprehensible universe where mathematics would be inefficient. Let us see whether it might help us again. Now we know that inflationary cosmology provides a possible answer to all of these questions.
Why is our universe so large? Why parallel lines do not intersect? Why different parts of the universe look so similar? For a long time such questions looked too metaphysical to be considered seriously. But shall we give up so easily? Let us consider several other questions of a similar type. This would match the words about a miracle and an undeserved gift. One could always respond that God created the universe and made it simple enough so that we can comprehend it. "The fact that it is comprehensible is a miracle." Similarly, Eugene Wigner said that the unreasonable efficiency of mathematics is "a wonderful gift which we neither understand nor deserve." Thus we have a problem that may seem too metaphysical to be addressed in a meaningful way: Why do we live in a comprehensible universe with certain rules, which can be efficiently used for predicting our future? "The most incomprehensible thing about the world is that it is comprehensible." This is one of the most famous quotes from Albert Einstein.
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