Our very existence imposes rules determining from where and at what time it is possible for us to observe the universe. That is, the fact of our being restricts the characteristics of the kind of environment in which we find ourselves. That principle is called the weak anthropic principle. (We’ll see shortly why the adjective “weak” is attached.) A better term than “anthropic principle” would have been “selection principle,” because the principle refers to how our own knowledge of our existence imposes rules that select, out of all the possible environments, only those environments with the
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