Ernst Zermelo  

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Ernst Zermelo in the 1900s


Born  "Berlin, "German Empire 
27 July 1871
Died  21 May 1953 "Freiburg im Breisgau, "West Germany 
(aged 81)
Nationality  "Germany 
Alma mater  "University of Berlin 
Known for  "Zermelo–Fraenkel set theory "Zermelo's navigation problem 
Awards  "Ackermann–Teubner Memorial Award (1916) 
Scientific career  
Fields  "Mathematics 
Institutions  "University of Zürich 
"Doctoral advisor  "Lazarus Fuchs "Hermann Schwarz 
Doctoral students  Stefan Straszewicz 
Ernst Friedrich Ferdinand Zermelo (German: "[t͡sɛrˈmeːlo]; 27 July 1871 – 21 May 1953) was a German "logician and "mathematician, whose work has major implications for the "foundations of mathematics. He is known for his role in developing "Zermelo–Fraenkel axiomatic set theory and his proof of the "wellordering theorem.
Ernst Zermelo graduated from Berlin's Luisenstädtisches Gymnasium (now HeinrichSchliemannOberschule ) in 1889. He then studied "mathematics, "physics and "philosophy at the universities of "Berlin, "Halle and "Freiburg. He finished his doctorate in 1894 at the "University of Berlin, awarded for a dissertation on the "calculus of variations (Untersuchungen zur Variationsrechnung). Zermelo remained at the University of Berlin, where he was appointed assistant to "Planck, under whose guidance he began to study "hydrodynamics. In 1897, Zermelo went to "Göttingen, at that time the leading centre for mathematical research in the world, where he completed his "habilitation thesis in 1899.
In 1910, Zermelo left Göttingen upon being appointed to the chair of mathematics at "Zurich University, which he resigned in 1916. He was appointed to an honorary chair at the "University of Freiburg in 1926, which he resigned in 1935 because he disapproved of Adolf Hitler's regime. At the end of "World War II and at his request, Zermelo was reinstated to his honorary position in Freiburg.
In 1900, in the Paris conference of the "International Congress of Mathematicians, "David Hilbert challenged the mathematical community with his famous "Hilbert's problems, a list of 23 unsolved fundamental questions which mathematicians should attack during the coming century. The first of these, a problem of "set theory, was the "continuum hypothesis introduced by "Cantor in 1878, and in the course of its statement Hilbert mentioned also the need to prove the "wellordering theorem.
Zermelo began to work on the problems of set theory under Hilbert's influence and in 1902 published his first work concerning the addition of "transfinite cardinals. By that time he had also discovered the socalled "Russell paradox. In 1904, he succeeded in taking the first step suggested by Hilbert towards the continuum hypothesis when he proved the "wellordering theorem (every set can be well ordered). This result brought fame to Zermelo, who was appointed Professor in Göttingen, in 1905. His proof of the "wellordering theorem, based on the powerset axiom and the "axiom of choice, was not accepted by all mathematicians, mostly because the axiom of choice was a paradigm of nonconstructive mathematics. In 1908, Zermelo succeeded in producing an improved proof making use of Dedekind's notion of the "chain" of a set, which became more widely accepted; this was mainly because that same year he also offered an "axiomatization of set theory.
Zermelo began to axiomatize set theory in 1905; in 1908, he published his results despite his failure to prove the consistency of his axiomatic system. See the article on "Zermelo set theory for an outline of this paper, together with the original axioms, with the original numbering.
In 1922, "Adolf Fraenkel and "Thoralf Skolem independently improved Zermelo's axiom system. The resulting 8 axiom system, now called "ZermeloFraenkel axioms (ZF), is now the most commonly used system for "axiomatic set theory.
Proposed in 1931, the "Zermelo's navigation problem is a classic "optimal control problem. The problem deals with a boat navigating on a body of water, originating from a point O to a destination point D. The boat is capable of a certain maximum speed, and we want to derive the best possible control to reach D in the least possible time.
Without considering external forces such as current and wind, the optimal control is for the boat to always head towards D. Its path then is a line segment from O to D, which is trivially optimal. With consideration of current and wind, if the combined force applied to the boat is nonzero the control for no current and wind does not yield the optimal path.
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