Algebraically Closed Field is Infinite

Theorem
Let $F$ be an algebraically closed field.

Then $F$ is infinite.

Proof
We prove the contrapositive: that a Galois field cannot be algebraically closed.

Let $F$ be Galois.

Define the polynomial:
 * $\displaystyle f \left({x}\right) = 1 + \prod_{a \mathop \in F} \left({x - a}\right)$

By definition, a field is a ring.

Thus by Ring Product with Zero:
 * $\displaystyle \forall x \in F: \prod_{a \mathop \in f} \left({x - a}\right) = 0$

But:
 * $\forall a \in F: f \left({a}\right) = 1 + 0 \ne 0$

Therefore $f \left({x}\right)$ cannot have a root in $F$.

Thus $F$ is not algebraically closed.

The result follows by the Rule of Transposition.