# What conditions does a Metrizable space have a Metrizable compactification?

## What conditions does a Metrizable space have a Metrizable compactification?

Under what conditions does a metrizable space have a metrizable compactification? SOLUTION. If A is a dense subset of a compact metric space, then A must be second countable because a compact metric space is second countable and a subspace of a second countable space is also second countable.

How do you find one point compactification?

The one-point compactification of a topological space X is a new compact space X*=X∪{∞} obtained by adding a single new point “∞” to the original space and declaring in X* the complements of the original closed compact subspaces to be open.

Is every Hausdorff space Metrizable?

Metrization theorems This states that every Hausdorff second-countable regular space is metrizable. So, for example, every second-countable manifold is metrizable. For example, a compact Hausdorff space is metrizable if and only if it is second-countable.

### How do you show a space is metrizable?

A topological space (X,T ) is said to be metrizable if there is a metric d on X that generates T . Due to the fact that very different looking metrics can generate the same topology, we usually talk about metrizable spaces rather than about metric spaces.

Which topology is metrizable?

A topology that is “potentially” a metric topology, in the sense that one can define a suitable metric that induces it.

Why is Q not locally compact?

It follows that all compact subsets of Q have empty interior (are nowhere dense) so Q can not be locally compact.

## What is compactification string theory?

A compactification of string theory is a solution in which four dimensions of spacetime are macroscopic and the other six form a compact manifold too small to have been observed.

Are normal spaces metrizable?

Any metrizable space, i.e., any space realized as the topological space for a metric space, is a perfectly normal space — it is a normal space and every closed subset of it is a G-delta subset (it is a countable intersection of open subsets).

Are all manifolds metrizable?

Assuming the usual definition of a topological manifold as a locally Euclidean space which is both Hausdorff and second-countable, it turns out that every manifold M is a metrizable space. This follows from example from Urysohn’s metrization theorem.

### Is every metrizable space normal?

Is Q locally connected?

The set of rational numbers Q is neither locally connected nor connected. The same is true for R in the lower limit topology. In fact, a totally disconnected space cannot be locally connected unless it has the discrete topology.

Which space are locally compact?

All discrete spaces are locally compact and Hausdorff (they are just the zero-dimensional manifolds). These are compact only if they are finite. All open or closed subsets of a locally compact Hausdorff space are locally compact in the subspace topology.

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