He was born in Saint Petersburg Russia.
Cantor recognized that infinite sets can have different sizes, distinguished between countable and uncountable sets and proved that the set of all rational numbers Q is countable while the set of all real numbers R is uncountable and hence strictly bigger. The proof uses his celebrated diagonal argument. In his later years, he tried in vain to prove the Continuum hypothesis. By 1897, he had discovered several paradoxes in elementary set theory.
Throughout the second half of his life he suffered from bouts of depression, which severely affected his ability to work and forced him to become hospitalized repeatedly. This recurrent depression would probably be diagnosed as bipolar disorder today. The discovery of Russell's paradox led to a nervous breakdown from which he never recovered. He started to publish about literature and religion, and developed his concept of the Absolute Infinite which he equated with God. He was impoverished during World War I and died in a mental hospital in Halle, Germany.
Cantor's innovative mathematics faced significant resistance during his lifetime. Modern mathematics completely accepts Cantor's work on transfinite sets and recognizes it as a paradigm shift of major importance.
See also: Cantor dust, Cantor set
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