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The fundamental groups of 3-dimensional spherical space forms


How can I understand the three-dimensional space forms?What's the notation for the intersection of stabilizer subgroups on a subset?Linear vs smooth actions of finite groups on spheres, Euclidean spaces and closed disksHow to show that $gamma_i(G) $/$gamma_i+1(G)$ has finite exponentTwo definitions of nilpotenceIn the lower central series of a group $G$, how to show each of the subgroups is fully invariant?Prove that $G$ is nilpotent if $G/Z(G)$ is nilpotent using lower central series.Actions of groups on categoriesIdentity for Lower Central SeriesFinite index subgroups in Amalgamated Free products













1












$begingroup$


Let $S^3/Gamma_i,(i=1,2)$ be a $3$-dimensional spherical space form, where $Gamma_i subset SO(4)$ is a finite subgroup acting freely on $S^3$. If $S^3/Gamma_1$ is homotopy equivalent to $S^3/Gamma_2$, can we find a $g in SO(4)$ such that
$$
gGamma_1 g^-1=Gamma_2?
$$










share|cite|improve this question









$endgroup$











  • $begingroup$
    On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
    $endgroup$
    – Qiaochu Yuan
    Mar 23 at 19:36















1












$begingroup$


Let $S^3/Gamma_i,(i=1,2)$ be a $3$-dimensional spherical space form, where $Gamma_i subset SO(4)$ is a finite subgroup acting freely on $S^3$. If $S^3/Gamma_1$ is homotopy equivalent to $S^3/Gamma_2$, can we find a $g in SO(4)$ such that
$$
gGamma_1 g^-1=Gamma_2?
$$










share|cite|improve this question









$endgroup$











  • $begingroup$
    On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
    $endgroup$
    – Qiaochu Yuan
    Mar 23 at 19:36













1












1








1





$begingroup$


Let $S^3/Gamma_i,(i=1,2)$ be a $3$-dimensional spherical space form, where $Gamma_i subset SO(4)$ is a finite subgroup acting freely on $S^3$. If $S^3/Gamma_1$ is homotopy equivalent to $S^3/Gamma_2$, can we find a $g in SO(4)$ such that
$$
gGamma_1 g^-1=Gamma_2?
$$










share|cite|improve this question









$endgroup$




Let $S^3/Gamma_i,(i=1,2)$ be a $3$-dimensional spherical space form, where $Gamma_i subset SO(4)$ is a finite subgroup acting freely on $S^3$. If $S^3/Gamma_1$ is homotopy equivalent to $S^3/Gamma_2$, can we find a $g in SO(4)$ such that
$$
gGamma_1 g^-1=Gamma_2?
$$







group-theory geometric-topology orthogonal-matrices low-dimensional-topology






share|cite|improve this question













share|cite|improve this question











share|cite|improve this question




share|cite|improve this question










asked Mar 21 at 14:38









TotoroTotoro

27415




27415











  • $begingroup$
    On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
    $endgroup$
    – Qiaochu Yuan
    Mar 23 at 19:36
















  • $begingroup$
    On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
    $endgroup$
    – Qiaochu Yuan
    Mar 23 at 19:36















$begingroup$
On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
$endgroup$
– Qiaochu Yuan
Mar 23 at 19:36




$begingroup$
On the other hand, see en.wikipedia.org/wiki/Mostow_rigidity_theorem.
$endgroup$
– Qiaochu Yuan
Mar 23 at 19:36










1 Answer
1






active

oldest

votes


















3












$begingroup$

This is not true in general, in fact it can fail for the lens spaces which are the quotients
$$L(p;q) = S^3 / Gamma(p;q)
$$

where $Gamma(p;q)$ is the cyclic subgroup of order $p$ in $SO(4)$ that is generated by the element described, in complex coordinates, by the formula
$$(z_1,z_2) mapsto (e^2 pi i/p cdot z_1, e^2 pi i q/p cdot z_2)
$$

The link given explains how to determine when $L(p;q_1)$ and $L(p;q_2)$ are homotopy equivalent and when they are homeomorphic, and these do not match up. And if they are not homeomorphic then there cannot be any $g in SO(4)$ for which $g Gamma(p;q_1) g^-1 = Gamma(p;q_2)$, because the map of $SO(4)$ determined by $g$ would descend to a homeomorphism between $L(p;q_1)$ and $L(p;q_2)$.






share|cite|improve this answer











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    1 Answer
    1






    active

    oldest

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    active

    oldest

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    active

    oldest

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    3












    $begingroup$

    This is not true in general, in fact it can fail for the lens spaces which are the quotients
    $$L(p;q) = S^3 / Gamma(p;q)
    $$

    where $Gamma(p;q)$ is the cyclic subgroup of order $p$ in $SO(4)$ that is generated by the element described, in complex coordinates, by the formula
    $$(z_1,z_2) mapsto (e^2 pi i/p cdot z_1, e^2 pi i q/p cdot z_2)
    $$

    The link given explains how to determine when $L(p;q_1)$ and $L(p;q_2)$ are homotopy equivalent and when they are homeomorphic, and these do not match up. And if they are not homeomorphic then there cannot be any $g in SO(4)$ for which $g Gamma(p;q_1) g^-1 = Gamma(p;q_2)$, because the map of $SO(4)$ determined by $g$ would descend to a homeomorphism between $L(p;q_1)$ and $L(p;q_2)$.






    share|cite|improve this answer











    $endgroup$

















      3












      $begingroup$

      This is not true in general, in fact it can fail for the lens spaces which are the quotients
      $$L(p;q) = S^3 / Gamma(p;q)
      $$

      where $Gamma(p;q)$ is the cyclic subgroup of order $p$ in $SO(4)$ that is generated by the element described, in complex coordinates, by the formula
      $$(z_1,z_2) mapsto (e^2 pi i/p cdot z_1, e^2 pi i q/p cdot z_2)
      $$

      The link given explains how to determine when $L(p;q_1)$ and $L(p;q_2)$ are homotopy equivalent and when they are homeomorphic, and these do not match up. And if they are not homeomorphic then there cannot be any $g in SO(4)$ for which $g Gamma(p;q_1) g^-1 = Gamma(p;q_2)$, because the map of $SO(4)$ determined by $g$ would descend to a homeomorphism between $L(p;q_1)$ and $L(p;q_2)$.






      share|cite|improve this answer











      $endgroup$















        3












        3








        3





        $begingroup$

        This is not true in general, in fact it can fail for the lens spaces which are the quotients
        $$L(p;q) = S^3 / Gamma(p;q)
        $$

        where $Gamma(p;q)$ is the cyclic subgroup of order $p$ in $SO(4)$ that is generated by the element described, in complex coordinates, by the formula
        $$(z_1,z_2) mapsto (e^2 pi i/p cdot z_1, e^2 pi i q/p cdot z_2)
        $$

        The link given explains how to determine when $L(p;q_1)$ and $L(p;q_2)$ are homotopy equivalent and when they are homeomorphic, and these do not match up. And if they are not homeomorphic then there cannot be any $g in SO(4)$ for which $g Gamma(p;q_1) g^-1 = Gamma(p;q_2)$, because the map of $SO(4)$ determined by $g$ would descend to a homeomorphism between $L(p;q_1)$ and $L(p;q_2)$.






        share|cite|improve this answer











        $endgroup$



        This is not true in general, in fact it can fail for the lens spaces which are the quotients
        $$L(p;q) = S^3 / Gamma(p;q)
        $$

        where $Gamma(p;q)$ is the cyclic subgroup of order $p$ in $SO(4)$ that is generated by the element described, in complex coordinates, by the formula
        $$(z_1,z_2) mapsto (e^2 pi i/p cdot z_1, e^2 pi i q/p cdot z_2)
        $$

        The link given explains how to determine when $L(p;q_1)$ and $L(p;q_2)$ are homotopy equivalent and when they are homeomorphic, and these do not match up. And if they are not homeomorphic then there cannot be any $g in SO(4)$ for which $g Gamma(p;q_1) g^-1 = Gamma(p;q_2)$, because the map of $SO(4)$ determined by $g$ would descend to a homeomorphism between $L(p;q_1)$ and $L(p;q_2)$.







        share|cite|improve this answer














        share|cite|improve this answer



        share|cite|improve this answer








        edited Mar 23 at 18:51









        janmarqz

        6,24741630




        6,24741630










        answered Mar 21 at 14:55









        Lee MosherLee Mosher

        51.6k33889




        51.6k33889



























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