In mathematics, the Milnor conjecture was a proposal by John Milnor (1970) of a description of the Milnor K-theory (mod 2) of a general field F with characteristic different from 2, by means of the Galois (or equivalently étale) cohomology of F with coefficients in Z/2Z. It was proved by Vladimir Voevodsky (1996, 2003a, 2003b).
Statement Let F be a field of characteristic different from 2. Then there is an isomorphism
K n M ( F ) / 2 ≅ H e ´ t n ( F , Z / 2 Z ) {\displaystyle K_{n}^{M}(F)/2\cong H_{{\acute {e}}t}^{n}(F,\mathbb {Z} /2\mathbb {Z} )}
for all n ≥ 0, where KM denotes the Milnor ring.
About the proof The proof of this theorem by Vladimir Voevodsky uses several ideas developed by Voevodsky, Alexander Merkurjev, Andrei Suslin, Markus Rost, Fabien Morel, Eric Friedlander, and others, including the newly minted theory of motivic cohomology (a kind of substitute for singular cohomology for algebraic varieties) and the motivic Steenrod algebra.
Generalizations The analogue of this result for primes other than 2 was known as the Bloch–Kato conjecture. Work of Voevodsky and Markus Rost yielded a complete proof of this conjecture in 2009; the result is now called the norm residue isomorphism theorem.
References Mazza, Carlo; Voevodsky, Vladimir; Weibel, Charles (2006), Lecture notes on motivic cohomology, Clay Mathematics Monographs, vol. 2, Providence, R.I.: American Mathematical Society, ISBN 978-0-8218-3847-1, MR 2242284 Milnor, John Willard (1970), "Algebraic K-theory and quadratic forms", Inventiones Mathematicae, 9 (4): 318–344, Bibcode:1970InMat...9..318M, doi:10.1007/BF01425486, ISSN 0020-9910, MR 0260844, S2CID 13549621 Voevodsky, Vladimir (1996), The Milnor Conjecture, Preprint Voevodsky, Vladimir (2003a), "Reduced power operations in motivic cohomology", Institut des Hautes Études Scientifiques. Publications Mathématiques, 98 (98): 1–57, arXiv:math/0107109, doi:10.1007/s10240-003-0009-z, ISSN 0073-8301, MR 2031198, S2CID 8172797 Voevodsky, Vladimir (2003b), "Motivic cohomology with Z/2-coefficients", Institut des Hautes Études Scientifiques. Publications Mathématiques, 98 (98): 59–104, doi:10.1007/s10240-003-0010-6, ISSN 0073-8301, MR 2031199, S2CID 54823073
Further reading Kahn, Bruno (2005), "La conjecture de Milnor (d'après V. Voevodsky)", in Friedlander, Eric M.; Grayson, D.R. (eds.), Handbook of K-theory (in French), vol. 2, Springer-Verlag, pp. 1105–1149, ISBN 3-540-23019-X, Zbl 1101.19001