ELI5: Explain Like I'm 5

Descendant tree (group theory)

Imagine you have a big family and you want to know how everyone is related to each other. So you make a family tree. A family tree shows you who your mom and dad are, and who their moms and dads are, and so on. It helps you understand how you are connected to all your relatives.

In group theory, we use something called a descendant tree to understand how different elements in a group are related to each other. Just like a family tree, a descendant tree shows us the relationships between elements in a group.

To understand this, let's first talk about what a group is. In math, a group is a collection of things (called elements) that have certain rules or properties. Elements in a group can be anything, like numbers, shapes, or even letters. For example, let's say we have a group of numbers: {1, 2, 3, 4, 5}. These are the elements in our group.

Now, let's say our group has a special operation called multiplication. When we multiply two elements in the group, we get another element in the group. For example, if we multiply 2 and 3, we get 6, which is also in our group.

In a descendant tree, we start with one element in the group and see what happens when we apply the operation to it. Then we see what happens when we apply the operation to the result, and so on. We keep going until we have explored all the elements we can reach.

Let's say we start with the number 2 in our group. We apply the multiplication operation to it and get 4. Then we apply the operation to 4 and get 8. We can keep going and see that if we keep applying the operation to the result, we get 16, 32, and so on.

So our descendant tree would look like this:

2
/ \
4 16
/ \
8 32

This tells us that starting from the number 2, we can multiply it by 2 to get 4, then multiply 4 by 2 to get 8, and so on.

But what if we start with a different number in our group, like 3? Let's see what happens:

3
/ \
9 27
/ \
81 243

Here, we see that starting from 3, if we multiply by 3 each time, we get 9, then 27, and so on.

By looking at these descendant trees, we can understand how different elements in the group are related to each other. We can see how they are connected through the multiplication operation. We can also see if there are any patterns or similarities between the different trees.

So, just like a family tree helps us understand how different relatives are related to each other, a descendant tree helps us understand how different elements in a group are related to each other through a special operation.