ELI5: Explain Like I'm 5

Domino (mathematics)

Have you ever played with dominoes before? You know those rectangular tiles with different numbers of dots on them? Well, in math, dominoes are a bit different.

In mathematics, dominoes are often used to represent pairs of numbers. For example, the domino piece with two dots on one half and three dots on the other half could represent the pair of numbers (2, 3).

Now, imagine a long line of these domino pieces, where the right end of one piece meets the left end of the next piece. This is called a domino chain. Each piece connects to two other pieces in the chain, just like in a game of dominoes.

Mathematicians are interested in finding out if certain patterns exist in these domino chains. To do this, they use something called the domino problem.

In the domino problem, you are given a starting domino, which represents a pair of numbers. From there, you need to add more dominoes to the chain, but there are rules you have to follow. Each new domino you add must share one number with the domino it’s next to, and that number cannot be shared by any other domino in the chain.

For example, let’s say the starting domino is (1, 2). The next domino you add could be (2, 5), because it shares the number 2 with the previous domino, and 5 is not shared by any other domino in the chain.

The domino problem asks if it's possible to create an infinitely long chain of dominoes following these rules. This is a challenging problem because there are many possible starting dominoes, and it's not clear whether or not an infinite chain exists for all of them.

By solving the domino problem and understanding the patterns in these chains, mathematicians are able to make important discoveries about number theory and other areas of math.
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