TITLE: Show that there doesn't exists a space $X$ such that $X\times X=S^{2}$.
QUESTION [9 upvotes]: Problem : Show that there doesn't exist a space $X$ such that $X\times X$ is homeomorphic to $S^{2}$, the 2-dimensional sphere. 

Is there any solution which doesn't use algebraic topology? I solved this problem by using Kunneth formula and there is another solution using homotopy group $\pi_{2}$. However, it seems that there might be an elementary proof that only uses general topology. If such space exists, we can prove that $X$ is connected and compact. Also, we can show that $X$ is simply-connected. Anything else? Thanks in advance.

REPLY [5 votes]: Here is an algebraic topology free answer, which uses several other big hammers instead.
Assume for a contradiction that $f:X\times X\rightarrow S^2$ is a homeomorhpism. 
Consider the involution $\sigma:X\times X\rightarrow X\times X$ which switches the factors:  $\sigma(x_1,x_2) = (x_2,x_1).$  Then $\rho = f\circ \sigma \circ f^{-1}$ is an involution of $S^2$.  According to Eilenberg (in a proof which doesn't use algebraic topology), $\rho$ is conjugate to a smooth map $\rho '$ in $Homeo(S^2)$ (Thanks to Balarka for noticing and fixing a previous gap here).  By averaging a Riemannian metric on $S^2$ we may assume that $\rho'$ is an isometry on $S^2$.  In particular, the fixed point set of $\rho'$ must be an embedded submanifold in $S^2$.  Note that the fixed point set of $\rho'$ is homeomorphic to the fixed point set of $\rho$.
Now, the fixed point set of $\sigma$ is the diagonal $\Delta X = \{(x, x)\in X\times X: x\in X\}$ so is clearly homeomorphic to $X$.  Since $f$ is a homeomorphism, we see the fixed point set of $\rho$, which is equal to $f(X)$, is homeomorphic to $X$.  Thus, we have shown that $X$ itself has the structure of a smooth manifold.
From the classification of compact 1-manifolds (which can be done via Riemannian geometry using the exponential map), it follows that $X$ is homeomorphic to $S^1$.  Therefore, $S^2$ is homeomorphic to $S^1\times S^1$.
Now, how do we show this is a contradiction without algebraic topology?  First, equip $S^2$ and $S^1\times S^1$ with their standard differentiable structures.
In this paper of Hatcher, he shows that any homeomorphism between smooth surfaces is isotopic to a diffeomorphism without using any results from algebraic topology.  Thus, we may assume $S^2$ is diffeomorphic to $S^1\times S^1$.
Finally, we note that $S^1\times S^1$ is parallelizable (obvious) while $S^2$ is not (less obvious), so they can't be diffeomorphic.  And while the standard proof of the Hairy Ball Theorem uses algebraic topology, Milnor has provided a proof which uses only some analysis and a bit of point set topology.