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  "body": "\n## Summary\n\nA contractible space is a topological space that has the [[homotopy type|SK0ZJGWXDP]] of a point.\nEquivalently, it is nonempty and its identity map can be deformed continuously into a constant map.\nAll homotopy groups and all reduced homology groups of a contractible space vanish.\nContractible spaces are the trivial objects of homotopy theory.\n\n## Explanations\n\n### L1 human\n\nA space is contractible when it can be shrunk continuously to a single point inside itself.\nA disk, a ball, a tree and the whole space $\\R^n$ are contractible.\nFor $\\R^n$, slide every point $x$ to the origin along the segment $(1 - t) x$.\nA circle is not contractible: shrinking it to a point would have to break it.\n",
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