[Math] In abstract algebra, what is an intuitive explanation for a field

abstract-algebrafield-theoryintuitionnumber theoryring-theory

Wikipedia has the following to say about fields.

In mathematics, a field is one of the fundamental algebraic structures used in abstract algebra. It is a nonzero commutative division ring, or equivalently a ring whose nonzero elements form an abelian group under multiplication. As such it is an algebraic structure with notions of addition, subtraction, multiplication, and division satisfying the appropriate abelian group equations and distributive law.

What is an intuitive way about thinking about a field?

Best Answer

Stimulated by the comments, I now realize that you’ve already seen many examples of fields. If you’ve had two years of high-school algebra, you know the fields $\Bbb Q$ of all rational numbers and $\Bbb R$ of all real numbers. But you know more.

It’s universal here in the States, at least, to ask students to “rationalize the denominator” in fractions like $$ \frac{1+3i}{2+4i}=\frac{(1+3i)(2-4i)}{(2+4i)(2-4i)} =\frac{14+2i}{20}=\frac{7+i}{10}=\frac7{10}+\frac1{10}i\,, $$ although teachers may not ask students to perform the last step. You see, though, that the complex numbers $\Bbb C$ of all $a+bi$ with $a,b\in\Bbb R$ are a field, and this example certainly lets you believe that the Gaussian numbers, all $a+bi$ with $a,b\in\Bbb Q$, also form a field.

I hope that in high school you also simplified fractions like $$ \frac{1+3\sqrt2}{2+4\sqrt2} =\frac{(1+3\sqrt2)(2-4\sqrt2)}{(2+4\sqrt2)(2-4\sqrt2)} =\frac{-22+2\sqrt2}{-28} =\frac{11-\sqrt2}{14}=\frac{11}{14}-\frac1{14}\sqrt2\,, $$ so that you now realize that the numbers of form $a+b\sqrt2$ (where now you must restrict $a$ and $b$ to rational numbers), also play nicely together to make up a field.

It would be wrong to say that fields are everywhere in Abstract Algebra, but if you know where to look, you’ll find them surprisingly often.