ELI5: Explain Like I'm 5

Riemann Xi function

Imagine you have a really big box that you want to fill up with toy blocks. You start putting in the blocks one by one, and every time you put in a block, you can hear a sound. The sound gets louder and louder as you keep adding more blocks.

Now imagine that instead of just adding one block at a time, you can add lots of blocks at once. Each time you add a bunch of blocks, you still hear a sound, but it's a little bit different than the sound you heard when you added just one block. If you add more and more blocks at once, the sound changes even more.

The Riemann Xi function is kind of like that sound that you hear when you add blocks to the box. But instead of blocks, it's all about prime numbers. A prime number is a number that can only be divided by 1 and itself, like 2, 3, 5, 7, 11, and so on. The Riemann Xi function tells us something about how many prime numbers there are.

When we add lots of prime numbers together, we get a new number that we call a "sum." Just like adding lots of blocks together makes a bigger and bigger pile, adding lots of prime numbers together makes a bigger and bigger sum. The Riemann Xi function helps us understand how those sums of prime numbers behave when we add more and more of them together.

Scientists use the Riemann Xi function to study something called the Riemann Hypothesis, which is a really big mystery about prime numbers. The Riemann Hypothesis says that there is a pattern in the way prime numbers are distributed, but nobody knows for sure what that pattern is. By studying the Riemann Xi function, scientists hope to find clues that will help them solve this mystery.