What is Infinity?

(Dedekind’s definition)

The Peano axiom was influenced by Dedekind.

What is Infinity?

(Dedekind’s definition)

The Peano axiom was influenced by Dedekind.

Julius Wilhelmina Richard Dedekind (6 Oct 1831 – 12 Feb 1916)

– Last student of Gauss at Göttingen

– Student and closed friend of Dirichlet who influenced his Mathematical education

– Introduced the word **Field** (Körper)

– Gave the first university course on Galois Theory

– Developed **Real** Number **‘Dedekind Cut**‘ in 1872

– Accomplished musician

– Never married, lived with his unmarried sister until death

– **“Whatever provable should be proved.”**

– By 1858: still yet established ?

– Gave strong support to Cantor on **Infinite** Set.

http://www-history.mcs.st-and.ac.uk/Biographies/Dedekind.html

Dedekind

(1831-1916)

Dedelind was the 1st person in the world to define Field:

“Any system of infinitely many real or complex numbers, which in itself is so ‘closed’ and complete, that +, – , *, / of any 2 numbers always produces a number of the same system.”

Heinrich Weber (1842-1913) gave the abstract definition of Field.

**Field Characteristic**

1. Field classification by Ernst Steinitz @ 1910

2. Given a Field, we start with the element that acts as 0, and repeatedly add the element that acts as 1.

3. If after p additions, we obtain 0 again, p must be prime number, and we say that the Field has characteristic p;

4. If we never get back to 0, the Field has characteristic 0. (e.g. Complex Field)

Example: GF(2) = {0,1|+} ; prime p = 2

1st + (start with 0):

0 + 1 = 1

2nd (=p) +:

1 + 1 = 0 => back to 0 again!

=> GF(2) characteristic p= 2

**Galois Field GF(p)**

1. For each prime p, there are infinitely many finite fields of characteristic p, known as Galois fields GF(p).

2. For each positive power of prime p, there is exactly **one** field.

*(This is the only IMPORTANT Theorem need to know in Field Theory)*

E.g. GF(2) = {0,1}

**Math Game: Chinese 9-Ring Puzzle (九连环 Jiu Lian Huan)**

To solve Chinese ancient 9-Ring Puzzle (九连环) needs a “Vector Space V(9,K) over Field K”

finite Field K = Galois Field GF(2) = {0,1|+,*}

and 9-dimension Vector Space V(9,K):

V(0)=(0,0,0,0,0,0,0,0,0) ->

V(j) =(0,0,… 0,1,..0,0) ->

V(9)= (0,0,0,0,0,0,0,0,1)

From start V(0) to ending V(9) = 511 steps.