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That is, let $f:X \rightarrow Y$ be a map of spaces such that $f_*: H_*(X) \rightarrow H_*(Y)$ induces an isomorphism on homology. We get an induced map $\tilde{f}: \Omega X \rightarrow \Omega Y$, where $\Omega X$ is the loop space of $x$. Does $\tilde{f}$ also induce an isomorphism on homology?

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    This is at least true if $X, Y$ are simply connected (or if the fundamental group acts trivially on the fibers); see Proposition 1.12 in Hatcher's book on spectral sequences.2011-03-23
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    You mean in the setting where $X$ and $Y$ are fibers of fibrations, and the fundamental group of the base acts trivially on the homology of the fibers? I want to use this to prove the Spectral Sequence theorem :)2011-03-23
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    @Tony: Whoops, yes, I meant that $\pi_1$ acts trivially on the *homologies*, not on the fibers themselves. This follows directly from the spectral sequence comparison theorem if I am not mistaken. (I'm not sure why you wouldn't prove the comparison theorem purely algebraically though.)2011-03-23
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    I'm not familiar enough with this comparison theorem to know if you guys are somehow implicitly referring to this, but if $X$ and $Y$ are simply-connected (or if $f_\#:\pi_1(X)\rightarrow \pi_1(Y)$ is an isomorphism) then $f$ is already a homotopy equivalence by the relative Hurewicz theorem and Whitehead's theorem.2011-03-24
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    @Aaron: Wait, doesn't this only work if $X,Y$ are CW complexes? (Or is it true that the loop space functor preserves weak equivalences?)2011-04-10
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    @Akhil: Yes I believe it is true, just from the fact that $\pi_n(\Omega f) = \pi_{n+1}(f)$ (and using Whitehead's theorem again).2011-04-13
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    @Aaron: Whoops! You're right, of course...2011-04-13
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    If the spaces are simply connected and CW spaces, then $f$ is actually a homotopical equivalence. If the spaces are not simply connected but $f$ induces an isomorphism on $\pi_1$ and an isomorphism on homology with local coefficients, the same holds.2014-12-05

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