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Sunday, April 10, 2011

Hilbert's problems

(excerpted from http://en.wikipedia.org/wiki/Hilbert%27s_problems)




Hilbert's twenty-three problems are:

Problem Brief explanation Status Year Solved
1st The continuum hypothesis (that is, there is no set whose cardinality is strictly between that of the integers and that of the real numbers) Proven to be impossible to prove or disprove within the Zermelo–Fraenkel set theory with or without the Axiom of Choice. There is no consensus on whether this is a solution to the problem. 1963
2nd Prove that the axioms of arithmetic are consistent. There is no consensus on whether results of Gödel and Gentzen give a solution to the problem as stated by Hilbert. Gödel's second incompleteness theorem, proved in 1931, shows that no proof of its consistency can be carried out within arithmetic itself. Gentzen proved in 1936 that the consistency of arithmetic follows from the well-foundedness of the ordinal ε0. 1936?
3rd Given any two polyhedra of equal volume, is it always possible to cut the first into finitely many polyhedral pieces which can be reassembled to yield the second? Resolved. Result: no, proved using Dehn invariants. 1900
4th Construct all metrics where lines are geodesics. Too vague to be stated resolved or not.[n 1]
5th Are continuous groups automatically differential groups? Resolved by Andrew Gleason, depending on how the original statement is interpreted. If, however, it is understood as an equivalent of the Hilbert–Smith conjecture, it is still unsolved. 1953?
6th Axiomatize all of physics Unresolved. [n 2]
7th Is a b transcendental, for algebraic a ≠ 0,1 and irrational algebraic b ? Resolved. Result: yes, illustrated by Gelfond's theorem or the Gelfond–Schneider theorem. 1935
8th The Riemann hypothesis ("the real part of any non-trivial zero of the Riemann zeta function is ½") and other prime number problems, among them Goldbach's conjecture and the twin prime conjecture Unresolved.
9th Find most general law of the reciprocity theorem in any algebraic number field Partially resolved.[n 3]
10th Find an algorithm to determine whether a given polynomial Diophantine equation with integer coefficients has an integer solution. Resolved. Result: impossible, Matiyasevich's theorem implies that there is no such algorithm. 1970
11th Solving quadratic forms with algebraic numerical coefficients. Partially resolved.[citation needed]
12th Extend the Kronecker–Weber theorem on abelian extensions of the rational numbers to any base number field. Unresolved.
13th Solve all 7-th degree equations using continuous functions of two parameters. Resolved. The problem was solved affirmatively by Vladimir Arnold based on work by Andrei Kolmogorov. [n 5] 1957
14th Is the ring of invariants of an algebraic group acting on a polynomial ring always finitely generated? Resolved. Result: no, counterexample was constructed by Masayoshi Nagata. 1959
15th Rigorous foundation of Schubert's enumerative calculus. Partially resolved.[citation needed]
16th Describe relative positions of ovals originating from a real algebraic curve and as limit cycles of a polynomial vector field on the plane. Unresolved.
17th Expression of definite rational function as quotient of sums of squares Resolved. Result: An upper limit was established for the number of square terms necessary.[citation needed] 1927
18th (a) Is there a polyhedron which admits only an anisohedral tiling in three dimensions?
(b) What is the densest sphere packing?
(a) Resolved. Result: yes (by Karl Reinhardt).
(b) Resolved by computer-assisted proof. Result: cubic close packing and hexagonal close packing, both of which have a density of approximately 74%.[n 6]
(a) 1928
(b) 1998
19th Are the solutions of Lagrangians always analytic? Resolved. Result: yes, proven by Ennio de Giorgi and, independently and using different methods, by John Forbes Nash. 1957
20th Do all variational problems with certain boundary conditions have solutions? Resolved. A significant topic of research throughout the 20th century, culminating in solutions[citation needed] for the non-linear case.
21st Proof of the existence of linear differential equations having a prescribed monodromic group Resolved. Result: Yes or no, depending on more exact formulations of the problem.[citation needed]
22nd Uniformization of analytic relations by means of automorphic functions Resolved.[citation needed]
23rd Further development of the calculus of variations Unresolved.

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