Pythagoras (548-495 BC) discovered irrational numbers. This discovery became the secret of a religious society formed by his followers known as the Order of the Pythagoreans. The exposure of this mathematical secret punishable by death is now known as the Pythagorean Crisis. From number theory of sets it is well known that the set of irrational numbers is infinitely larger than the set of whole numbers which is also known to be infinitely large. This crisis emerges in relation to the problem of comparing a line segment expressible in whole numbers with that of another.
If one compares a short segment R with a longer segment S, it is possible R can fit exactly a whole number of times into S. This possibility implies that R is a measure of S and S is a multiple of R. Moreover, if R does not fit exactly it is still possible to find a smaller segment T that fits a whole number of times into both R and S. In this case, T is known as a common measure of both R and S and the ratio S/R is a rational number called an improper fraction or a mixed number as the sum of a whole number and a proper fraction where the numerator is always lesser than the denominator. However, a simple proof can be shown that the side R and diagonal S of a square do not have a common measure. By the Pythogorean Theorem S²=2R². If a common measure exists then S=M/N and M and N are both whole numbers. Furthermore, M/N is given in lowest terms which imply that M and N cannot be both even numbers but if M is even then M² is also even. Consequently, there exists a whole number K such that M=2K then M²=4K²=2N² where S=MT and R=NT. That is N and N² are also both even thus showing a proof by contradiction known as reductio ad absurdum.


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