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Inverse Galois problem over Q

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Problem. Prove or disprove: for every finite group GG there is a finite Galois extension L/QL/\mathbb Q with

Gal⁡(L/Q)≅G.\operatorname{Gal}(L/\mathbb Q)\cong G .

Equivalently, for every finite group GG there is a monic irreducible polynomial f∈Q[x]f\in\mathbb Q[x] whose splitting field over Q\mathbb Q has Galois group isomorphic to GG. The two forms agree because every finite Galois extension of Q\mathbb Q is the splitting field of the minimal polynomial of a primitive element.

A stronger variant is the regular inverse Galois problem: for every finite group GG, find a Galois extension L/Q(t)L/\mathbb Q(t) with Gal⁡(L/Q(t))≅G\operatorname{Gal}(L/\mathbb Q(t))\cong G and L∩Q‾=QL\cap\overline{\mathbb Q}=\mathbb Q. By Hilbert's irreducibility theorem, a regular realization specializes at infinitely many t0∈Qt_0\in\mathbb Q to Galois extensions of Q\mathbb Q with group GG. So a positive answer to the regular problem implies a positive answer here. The problem here is the one over Q\mathbb Q as stated above.

Background

The question goes back to Hilbert's 1892 irreducibility theorem, which he used to realize the symmetric and alternating groups over Q\mathbb Q. Emmy Noether proposed a geometric approach in 1918. If the fixed field Q(x1,…,xn)G\mathbb Q(x_1,\dots,x_n)^G of a permutation action is purely transcendental, then GG has a regular realization. Swan showed that this fails for the cyclic group of order 4747, so Noether's approach cannot work for all groups [2].

The most productive general method is rigidity. It uses rational rigid tuples of conjugacy classes to produce GG-covers of P1\mathbb P^1 defined over Q\mathbb Q, branched over three or more points, hence regular realizations [2, 3]. Thompson used it to realize the Monster group [4]. Other approaches use embedding problems, which proceed by lifting a realization of a quotient of GG, and arithmetic geometry, including rational points on moduli spaces of covers and Galois representations attached to modular forms [1, 2].

References
  1. O. Wittenberg, "Around the inverse Galois problem", in Number Theory Informed by Computation, IAS/Park City Math. Ser. 29, AMS (2025), 291–322. doi:10.1090/pcms/029/08
  2. G. Malle and B. H. Matzat, Inverse Galois Theory, 2nd ed., Springer Monographs in Math., Springer (2018). doi:10.1007/978-3-662-55420-3
  3. H. Völklein, Groups as Galois Groups: An Introduction, Cambridge Stud. Adv. Math. 53, Cambridge Univ. Press (1996). doi:10.1017/CBO9780511471117
  4. J. G. Thompson, "Some finite groups which appear as Gal⁡L/K\operatorname{Gal}L/K, where K⊆Q(μn)K\subseteq\mathbb Q(\mu_n)", J. Algebra 89 (1984), 437–499. doi:10.1016/0021-8693(84)90228-X
  5. I. R. Šafarevič, "Construction of fields of algebraic numbers with given solvable Galois group", Amer. Math. Soc. Transl. (2) 4 (1956), 185–237. doi:10.1090/trans2/004/08
  6. J. Neukirch, A. Schmidt and K. Wingberg, Cohomology of Number Fields, 2nd ed., Grundlehren Math. Wiss. 323, Springer (2008), Chapter IX. doi:10.1007/978-3-540-37889-1
  7. X. Huang, B. Jackson, K.-H. Lee, B. Poonen, R. Pries and S. Zhang, "The Mathieu group M23M_{23} is a Galois group over Q\mathbb Q", preprint (2026). arXiv:2608.08538
  8. Wikipedia, Inverse Galois problem.

Source: Wikipedia

Progress summary

Refreshed
Open · progress reported

The general question remains open, while August claims cover one long-standing exceptional case and all groups in degree 24, without independent verification.

The inverse Galois problem asks whether every finite group occurs as the Galois group of an extension of Q\mathbb{Q}. Posed in the early nineteenth century, it remains unresolved in general.

Known results

  • Hilbert realized SnS_n and AnA_n over Q\mathbb{Q}.
  • Scholz and Reichardt (1937) realized every odd pp-group.
  • Shafarevich (1954; proof corrected in 1989) realized every finite solvable group.
  • By 1989, 2525 of the 2626 sporadic simple groups were realized over Q\mathbb{Q}.

August 2026 claimed advances

On August 11, 2026, Huang, Jackson, Lee, Poonen, Pries, and Zhang were reported to have constructed a degree-2323 polynomial with Galois group M23M_{23}, completing the sporadic cases; the claim is unverified. On August 8, 2026, the IGP24 competition announced realizations for all approximately 25,00025{,}000 degree-2424 groups, also without independent verification. Neither claim resolves arbitrary finite groups.

Current status (as of September 2026): Realizability over Q\mathbb{Q} is settled for all finite solvable groups and many nonsolvable families; recent claims cover M23M_{23} and degree-2424 groups, but the general problem remains open and those claims are unverified.

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