A field is just a fancy way of saying “a set of numbers that follows certain rules.” And by “finite,” we mean there are only so many elements in this set no infinite nonsense here!
So what exactly do these finite subgroups look like? Well, let’s take the example of the field of integers modulo n (or, as mathematicians call it, Z/nZ). This is a fancy way of saying “the set of numbers that are equivalent to each other when we divide by n.” For instance, 3 and 15 both have a remainder of 3 when you divide them by 6 so they’re considered the same in this context!
Now let’s say we want to find all the finite subgroups of Z/nZ. Well, it turns out that there are only two possibilities: either our group has order n (meaning it contains exactly one element for each non-zero residue class) or it has order d where d is a proper divisor of n (meaning it contains multiple elements for some residue classes).
So let’s take the example of Z/12Z. The subgroups with order 12 are just the trivial group {0} and the whole group itself, since there’s only one non-zero element that has a remainder of zero when we divide by 12 (namely, 0). But what about the other possible orders?
Well, let’s see if any subgroups have order 6. To do this, we need to find all the elements in Z/12Z that are their own inverse (meaning they multiply with themselves to get 1) and then check which ones generate a group of order 6. And guess what? There’s only one such element namely, [6]!
So we have our subgroup: {[0], [6]} is a cyclic group of order 6 that consists of all the even numbers in Z/12Z (since any multiple of 6 will be equivalent to either 0 or 6). And there you have it finite subgroups of fields, made simple!
Of course, this was just one example and there are many more fascinating things to explore in this area. But for now, let’s all take a deep breath and appreciate the beauty of math without getting too bogged down by its technicalities.