I asked recently on MO about algebraic structures admitted by topologically homogenous continua like the Hilbert cube $\ I^{\mathbb N}\ $ or the Knaster pseudo-arc. There is a relation between the algebraic and geometric structures in this context. And this is the topic of this post.
Let $\ *\ $ stand for a single-point space. Let us consider the following 3 properties of a compact space $\ X$:
- (C0) -- $X\ $ is acyclic, meaning that $\ H^*(X;\mathbb Z) = H^*(*;\mathbb Z)$;
- (C1) -- $X\ $ has a shape of a single-point space, i.e. every continuous map of $\ X\ $ into any (compact finite) polyhedron is homotopic to a constant map;
- (C2) -- $X\ $ is contractible.
Of course $\ (C2)\Rightarrow (C1)\Rightarrow (C0).\ $ Now the following three conjectures are open (or someone may provide a reference):
(Hk) If a continuum $\ X\ $ ($|X|>1$) has property (Ck) then there does not exist a homogenous metric in $\ X\ $ which induces the topology of $\ X$;
for $\ k=0\ 1\ 2.\ $
MOTIVATION: if a metric compact space $\ X\ $ admits a structure of a left or right quotient $\ G/H\ $ where $\ G\ $ is a compact metric group, and $\ H\ $ is a closed (not necessarily normal) subgroup of $\ G\ $ then $\ X\ $ admits a homegenous metric which induces the given topology. Indeed, one can apply the Haar measure on $\ G$; first to obtain a homogenous metric on $\ G$, and then again on $\ X=G/H\ $ itself (I hope this is right).