Julius Wilhelm Richard Dedekind (6 October 1831 – 12 February 1916) was a German
mathematician who made important contributions to
number theory,
abstract algebra
In mathematics, more specifically algebra, abstract algebra or modern algebra is the study of algebraic structures. Algebraic structures include groups, rings, fields, modules, vector spaces, lattices, and algebras over a field. The term ' ...
(particularly
ring theory), and
the
axiomatic foundations of arithmetic. His best known contribution is the definition of
real numbers through the notion of
Dedekind cut. He is also considered a pioneer in the development of modern
set theory and of the
philosophy of mathematics
The philosophy of mathematics is the branch of philosophy that studies the assumptions, foundations, and implications of mathematics. It aims to understand the nature and methods of mathematics, and find out the place of mathematics in people ...
known as ''
Logicism''.
Life
Dedekind's father was Julius Levin Ulrich Dedekind, an administrator of
Collegium Carolinum in
Braunschweig
Braunschweig () or Brunswick ( , from Low German ''Brunswiek'' , Braunschweig dialect: ''Bronswiek'') is a city in Lower Saxony, Germany, north of the Harz Mountains at the farthest navigable point of the river Oker, which connects it to the Nor ...
. His mother was Caroline Henriette Dedekind (née Emperius), the daughter of a professor at the Collegium. Richard Dedekind had three older siblings. As an adult, he never used the names Julius Wilhelm. He was born in Braunschweig (often called "Brunswick" in English), which is where he lived most of his life and died.
He first attended the Collegium Carolinum in 1848 before transferring to the
University of Göttingen
The University of Göttingen, officially the Georg August University of Göttingen, (german: Georg-August-Universität Göttingen, known informally as Georgia Augusta) is a public research university in the city of Göttingen, Germany. Founded i ...
in 1850. There, Dedekind was taught
number theory by professor
Moritz Stern.
Gauss
Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
was still teaching, although mostly at an elementary level, and Dedekind became his last student. Dedekind received his doctorate in 1852, for a thesis titled ''Über die Theorie der Eulerschen Integrale'' ("On the Theory of
Eulerian integrals"). This thesis did not display the talent evident by Dedekind's subsequent publications.
At that time, the
University of Berlin
Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative o ...
, not
Göttingen, was the main facility for mathematical research in Germany. Thus Dedekind went to Berlin for two years of study, where he and
Bernhard Riemann
Georg Friedrich Bernhard Riemann (; 17 September 1826 – 20 July 1866) was a German mathematician who made contributions to analysis, number theory, and differential geometry. In the field of real analysis, he is mostly known for the first rig ...
were contemporaries; they were both awarded the
habilitation in 1854. Dedekind returned to Göttingen to teach as a ''
Privatdozent'', giving courses on
probability and
geometry. He studied for a while with
Peter Gustav Lejeune Dirichlet, and they became good friends. Because of lingering weaknesses in his mathematical knowledge, he studied
elliptic
In mathematics, an ellipse is a plane curve surrounding two focal points, such that for all points on the curve, the sum of the two distances to the focal points is a constant. It generalizes a circle, which is the special type of ellipse in ...
and
abelian function
In mathematics, particularly in algebraic geometry, complex analysis and algebraic number theory, an abelian variety is a projective algebraic variety that is also an algebraic group, i.e., has a group law that can be defined by regular functio ...
s. Yet he was also the first at Göttingen to lecture concerning
Galois theory. About this time, he became one of the first people to understand the importance of the notion of
groups
A group is a number of persons or things that are located, gathered, or classed together.
Groups of people
* Cultural group, a group whose members share the same cultural identity
* Ethnic group, a group whose members share the same ethnic ide ...
for
algebra
Algebra () is one of the broad areas of mathematics. Roughly speaking, algebra is the study of mathematical symbols and the rules for manipulating these symbols in formulas; it is a unifying thread of almost all of mathematics.
Elementary a ...
and
arithmetic
Arithmetic () is an elementary part of mathematics that consists of the study of the properties of the traditional operations on numbers—addition, subtraction, multiplication, division, exponentiation, and extraction of roots. In the 19th c ...
.
In 1858, he began teaching at the
Polytechnic school in
Zürich (now ETH Zürich). When the Collegium Carolinum was upgraded to a ''
Technische Hochschule
A ''Technische Hochschule'' (, plural: ''Technische Hochschulen'', abbreviated ''TH'') is a type of university focusing on engineering sciences in Germany. Previously, it also existed in Austria, Switzerland, the Netherlands (), and Finland (, ). ...
'' (Institute of Technology) in 1862, Dedekind returned to his native Braunschweig, where he spent the rest of his life, teaching at the Institute. He retired in 1894, but did occasional teaching and continued to publish. He never married, instead living with his sister Julia.
Dedekind was elected to the Academies of Berlin (1880) and Rome, and to the
French Academy of Sciences (1900). He received honorary doctorates from the universities of
Oslo,
Zurich, and
Braunschweig
Braunschweig () or Brunswick ( , from Low German ''Brunswiek'' , Braunschweig dialect: ''Bronswiek'') is a city in Lower Saxony, Germany, north of the Harz Mountains at the farthest navigable point of the river Oker, which connects it to the Nor ...
.
Work
While teaching calculus for the first time at the
Polytechnic school, Dedekind developed the notion now known as a
Dedekind cut (German: ''Schnitt''), now a standard definition of the real numbers. The idea of a cut is that an
irrational number
In mathematics, the irrational numbers (from in- prefix assimilated to ir- (negative prefix, privative) + rational) are all the real numbers that are not rational numbers. That is, irrational numbers cannot be expressed as the ratio of two inte ...
divides the
rational numbers into two classes (
sets), with all the numbers of one class (greater) being strictly greater than all the numbers of the other (lesser) class. For example, the
square root of 2 defines all the nonnegative numbers whose squares are less than 2 and the negative numbers into the lesser class, and the positive numbers whose squares are greater than 2 into the greater class. Every location on the number line continuum contains either a rational or an irrational number. Thus there are no empty locations, gaps, or discontinuities. Dedekind published his thoughts on irrational numbers and Dedekind cuts in his pamphlet "Stetigkeit und irrationale Zahlen" ("Continuity and irrational numbers"); in modern terminology, ''Vollständigkeit'', ''
completeness''.
Dedekind defined two sets to be "similar" when there exists a
one-to-one correspondence between them. He invoked similarity to give the first precise definition of an
infinite set: a set is infinite when it is "similar to a proper part of itself," in modern terminology, is
equinumerous to one of its
proper subsets. Thus the set N of
natural numbers can be shown to be similar to the subset of N whose members are the
squares of every member of N, (N
→ N
2):
N 1 2 3 4 5 6 7 8 9 10 ...
↓
N
2 1 4 9 16 25 36 49 64 81 100 ...
Dedekind's work in this area anticipated that of
Georg Cantor, who is commonly considered the founder of
set theory. Likewise, his contributions to the
foundations of mathematics
Foundations of mathematics is the study of the philosophical and logical and/or algorithmic basis of mathematics, or, in a broader sense, the mathematical investigation of what underlies the philosophical theories concerning the nature of mathe ...
anticipated later works by major proponents of
Logicism, such as
Gottlob Frege and
Bertrand Russell
Bertrand Arthur William Russell, 3rd Earl Russell, (18 May 1872 – 2 February 1970) was a British mathematician, philosopher, logician, and public intellectual. He had a considerable influence on mathematics, logic, set theory, linguistics, ar ...
.
Dedekind edited the collected works of
Lejeune Dirichlet,
Gauss
Johann Carl Friedrich Gauss (; german: Gauß ; la, Carolus Fridericus Gauss; 30 April 177723 February 1855) was a German mathematician and physicist who made significant contributions to many fields in mathematics and science. Sometimes refer ...
, and
Riemann. Dedekind's study of Lejeune Dirichlet's work led him to his later study of
algebraic number field
In mathematics, an algebraic number field (or simply number field) is an extension field K of the field of rational numbers such that the field extension K / \mathbb has finite degree (and hence is an algebraic field extension).
Thus K is a f ...
s and
ideal
Ideal may refer to:
Philosophy
* Ideal (ethics), values that one actively pursues as goals
* Platonic ideal, a philosophical idea of trueness of form, associated with Plato
Mathematics
* Ideal (ring theory), special subsets of a ring considered ...
s. In 1863, he published Lejeune Dirichlet's lectures on
number theory as ''
Vorlesungen über Zahlentheorie'' ("Lectures on Number Theory") about which it has been written that:
The 1879 and 1894 editions of the ''Vorlesungen'' included supplements introducing the notion of an ideal, fundamental to
ring theory. (The word "Ring", introduced later by
Hilbert, does not appear in Dedekind's work.) Dedekind defined an
ideal
Ideal may refer to:
Philosophy
* Ideal (ethics), values that one actively pursues as goals
* Platonic ideal, a philosophical idea of trueness of form, associated with Plato
Mathematics
* Ideal (ring theory), special subsets of a ring considered ...
as a subset of a set of numbers, composed of
algebraic integer
In algebraic number theory, an algebraic integer is a complex number which is integral over the integers. That is, an algebraic integer is a complex root of some monic polynomial (a polynomial whose leading coefficient is 1) whose coefficients ...
s that satisfy polynomial equations with
integer coefficients. The concept underwent further development in the hands of Hilbert and, especially, of
Emmy Noether. Ideals generalize
Ernst Eduard Kummer's
ideal numbers, devised as part of Kummer's 1843 attempt to prove
Fermat's Last Theorem. (Thus Dedekind can be said to have been Kummer's most important disciple.) In an 1882 article, Dedekind and
Heinrich Martin Weber
Heinrich Martin Weber (5 March 1842, Heidelberg, Germany – 17 May 1913, Straßburg, Alsace-Lorraine, German Empire, now Strasbourg, France) was a German mathematician. Weber's main work was in algebra, number theory, and analysis. He ...
applied ideals to
Riemann surfaces, giving an algebraic proof of the
Riemann–Roch theorem
The Riemann–Roch theorem is an important theorem in mathematics, specifically in complex analysis and algebraic geometry, for the computation of the dimension of the space of meromorphic functions with prescribed zeros and allowed poles. It re ...
.
In 1888, he published a short monograph titled ''Was sind und was sollen die Zahlen?'' ("What are numbers and what are they good for?" Ewald 1996: 790), which included his definition of an
infinite set. He also proposed an
axiom
An axiom, postulate, or assumption is a statement that is taken to be true, to serve as a premise or starting point for further reasoning and arguments. The word comes from the Ancient Greek word (), meaning 'that which is thought worthy or f ...
atic foundation for the natural numbers, whose primitive notions were the number
one
1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. I ...
and the
successor function
In mathematics, the successor function or successor operation sends a natural number to the next one. The successor function is denoted by ''S'', so ''S''(''n'') = ''n'' +1. For example, ''S''(1) = 2 and ''S''(2) = 3. The successor functi ...
. The next year,
Giuseppe Peano
Giuseppe Peano (; ; 27 August 1858 – 20 April 1932) was an Italian mathematician and glottologist. The author of over 200 books and papers, he was a founder of mathematical logic and set theory, to which he contributed much notation. The stan ...
, citing Dedekind, formulated an equivalent but simpler
set of axioms, now the standard ones.
Dedekind made other contributions to
algebra
Algebra () is one of the broad areas of mathematics. Roughly speaking, algebra is the study of mathematical symbols and the rules for manipulating these symbols in formulas; it is a unifying thread of almost all of mathematics.
Elementary a ...
. For instance, around 1900, he wrote the first papers on
modular lattices. In 1872, while on holiday in
Interlaken, Dedekind met
Georg Cantor. Thus began an enduring relationship of mutual respect, and Dedekind became one of the first mathematicians to admire Cantor's work concerning infinite sets, proving a valued ally in Cantor's disputes with
Leopold Kronecker, who was philosophically opposed to Cantor's
transfinite numbers
In mathematics, transfinite numbers are numbers that are "infinite" in the sense that they are larger than all finite numbers, yet not necessarily absolutely infinite. These include the transfinite cardinals, which are cardinal numbers used to qu ...
.
Bibliography
Primary literature in English:
*1890. "Letter to Keferstein" in
Jean van Heijenoort, 1967. ''A Source Book in Mathematical Logic, 1879–1931''. Harvard Univ. Press: 98–103.
* 1963 (1901). ''Essays on the Theory of Numbers''. Beman, W. W., ed. and trans. Dover. Contains English translations of
Stetigkeit und irrationale Zahlen' and ''Was sind und was sollen die Zahlen?''
* 1996. ''Theory of Algebraic Integers''. Stillwell, John, ed. and trans. Cambridge Uni. Press. A translation of ''Über die Theorie der ganzen algebraischen Zahlen''.
* Ewald, William B., ed., 1996. ''From Kant to Hilbert: A Source Book in the Foundations of Mathematics'', 2 vols. Oxford Uni. Press.
**1854. "On the introduction of new functions in mathematics," 754–61.
**1872. "Continuity and irrational numbers," 765–78. (translation of ''Stetigkeit...'')
**1888. ''What are numbers and what should they be?'', 787–832. (translation of ''Was sind und...'')
**1872–82, 1899. Correspondence with Cantor, 843–77, 930–40.
Primary literature in German:
Gesammelte mathematische Werke(Complete mathematical works, Vol. 1–3).
Retrieved 5 August 2009.
See also
*
List of things named after Richard Dedekind
*
Dedekind cut
*
Dedekind domain
*
Dedekind eta function
*
Dedekind-infinite set
In mathematics, a set ''A'' is Dedekind-infinite (named after the German mathematician Richard Dedekind) if some proper subset ''B'' of ''A'' is equinumerous to ''A''. Explicitly, this means that there exists a bijective function from ''A'' onto ...
*
Dedekind number
File:Monotone Boolean functions 0,1,2,3.svg, 400px, The free distributive lattices of monotonic Boolean functions on 0, 1, 2, and 3 arguments, with 2, 3, 6, and 20 elements respectively (move mouse over right diagram to see description)
circle 6 ...
*
Dedekind psi function
In number theory, the Dedekind psi function is the multiplicative function on the positive integers defined by
: \psi(n) = n \prod_\left(1+\frac\right),
where the product is taken over all primes p dividing n. (By convention, \psi(1), which is ...
*
Dedekind sum In mathematics, Dedekind sums are certain sums of products of a sawtooth function, and are given by a function ''D'' of three integer variables. Dedekind introduced them to express the functional equation of the Dedekind eta function. They ha ...
*
Dedekind zeta function
*
Ideal (ring theory)
Notes
References
*
Further reading
*
Edwards, H. M., 1983, "Dedekind's invention of ideals," ''Bull. London Math. Soc. 15'': 8–17.
*
*Gillies, Douglas A., 1982. ''Frege, Dedekind, and Peano on the foundations of arithmetic''. Assen, Netherlands: Van Gorcum.
*
Ivor Grattan-Guinness, 2000. ''The Search for Mathematical Roots 1870–1940''. Princeton Uni. Press.
There is a
online bibliographyof the secondary literature on Dedekind. Also consult Stillwell's "Introduction" to Dedekind (1996).
External links
*
*
*
Dedekind, Richard, ''Essays on the Theory of Numbers.'' Open Court Publishing Company, Chicago, 1901.at the
Internet Archive
* Dedekind's Contributions to the Foundations of Mathematics http://plato.stanford.edu/entries/dedekind-foundations/.
{{DEFAULTSORT:Dedekind, Julius Wilhelm Richard
1831 births
1916 deaths
19th-century German mathematicians
19th-century German philosophers
20th-century German mathematicians
ETH Zurich faculty
Technical University of Braunschweig faculty
University of Göttingen alumni
University of Göttingen faculty
Humboldt University of Berlin alumni
Number theorists
Algebraists
Scientists from Braunschweig
People from the Duchy of Brunswick
Members of the French Academy of Sciences
Philosophers of mathematics