The Multiverse Long time ago when I was talking about string theory with my friend, he suggested me to take a look at the multiverse. So, I went to Youtube and watched a video called "Is There A Multiverse?". In the video, the theory given by the well-known physicist, Brian Greene, is that, there might be infinite number of universe! I think this is the most cool and interesting idea in the (world? universe? multiverse!) Imaging you are sitting around a desk and feeling bored. You notice that there is a pile of cards on the desk. So you want to kill the time by repeatedly picking 4 cards, putting them back to the pile, and shuffling all the cards. Your first 4 cards, let's say, are 3 of club, 5 of diamond, 8 of spade and K of diamond. As long as you repeat this picking process for enough times, you will see that your first combination of cards appears again and again. Similarly, our universe (your first 4 cards) will appear again and again if there are sufficient number of universe (enough number of picking process). If the theory that there are infinite number of universe is true, we can always find an universe that is exactly the same as ours. In another words, you can find someone doing the same thing, thinking the same way and acting the same behaviour as you outside our universe! I think it is pretty cool that we can find duplicates of us in other universe. But I find some problems behind the multiverse theory. 1. Can our universe be encoded using a finite number? We know that our 4 cards can be encoded by a finite number k, since there are totally Binomial(52, 4) = 270725 combinations. If we know that our cards are the k-th combination, we can decode our cards from the finite number k. But how to encode our universe? Is it possible to encode me using the time-space coordinating system? If you say that both time and space are discrete based on quantum mechanics, I would ask what the start point and end point of time is of our universe? If our universe cannot be encoded using a finite number, there might be impossible to find another universe that is exactly the same as ours. 2. Even if our universe can be encoded by a finite number, it is not always true that we can find an universe that is exactly the same as ours if there are infinite number of universe. For example, given the number 0.30303030303... that is infinitely repeating, we can not say that it contains the digit 8. So, the multiverse theory is unimaginable and I finally decide to forget it.