🧮History of Mathematics Unit 3 – Pythagoras and Number Theory

Origins and Historical Context

• Pythagoras of Samos, an ancient Greek philosopher and mathematician, lived around 570-495 BCE
• Pythagoras founded a philosophical and religious school in Croton, a Greek colony in southern Italy (around 530 BCE)
• The Pythagorean school combined mathematical study with philosophical and religious beliefs
• Pythagoreans believed in the transmigration of souls and followed a strict way of life that included vegetarianism and secrecy
• Pythagoras and his followers made significant contributions to mathematics, music theory, and astronomy
• The political and social climate of ancient Greece, particularly the Greek colonies in southern Italy, influenced the development and spread of Pythagorean ideas
• Pythagoras likely traveled to Egypt and Babylon, where he may have been exposed to mathematical knowledge from these ancient civilizations

Key Figures and Their Contributions

• Pythagoras, the founder of the Pythagorean school, is credited with the famous Pythagorean theorem and the discovery of the mathematical basis of musical harmony
  • However, the historical accuracy of these attributions is uncertain due to the secrecy of the Pythagorean school and the lack of reliable sources
• Hippasus of Metapontum, a Pythagorean, is believed to have discovered the existence of irrational numbers, which challenged the Pythagorean belief in the supremacy of whole numbers and ratios
• Philolaus, a prominent Pythagorean philosopher, wrote a book on Pythagorean doctrines that influenced later philosophers such as Plato and Aristotle
• Archytas of Tarentum, a Pythagorean mathematician and statesman, made contributions to geometry, mechanics, and music theory
  • He is known for his solution to the problem of doubling the cube using geometric constructions
• Theano, Pythagoras's wife or daughter, is said to have led the Pythagorean school after his death and made contributions to mathematics and philosophy

Pythagorean Theorem and Its Proofs

• The Pythagorean theorem states that in a right-angled triangle, the square of the hypotenuse (the side opposite the right angle) is equal to the sum of the squares of the other two sides (called the legs or catheti)
• Mathematically, the theorem is expressed as $a^2 + b^2 = c^2$, where $c$ is the length of the hypotenuse and $a$ and $b$ are the lengths of the legs
• The theorem has numerous proofs, including:
  • The geometric proof using the rearrangement of squares
  • The algebraic proof using the similarity of triangles
  • The proof using the concept of congruent triangles
• The Pythagorean theorem has applications in various fields, such as architecture, engineering, and navigation
• The theorem can be generalized to higher dimensions, known as the Pythagorean theorem in n-dimensional space
• The converse of the Pythagorean theorem states that if the square of the longest side of a triangle is equal to the sum of the squares of the other two sides, then the triangle is a right-angled triangle

Pythagorean School and Philosophy

• The Pythagorean school combined mathematical study with philosophical and religious beliefs, emphasizing the importance of numbers and their relationships in understanding the universe
• Pythagoreans believed that "all is number" and that the universe could be explained through mathematical relationships
• The school had a hierarchical structure, with different levels of initiation and knowledge
  • The most advanced members, known as the "mathematikoi," devoted themselves entirely to the study of mathematics and philosophy
• Pythagoreans believed in the transmigration of souls (reincarnation) and followed a strict way of life that included vegetarianism, secrecy, and the observance of various rituals
• The Pythagorean concept of harmony extended beyond mathematics to music theory, as they discovered the mathematical basis of musical intervals
• Pythagorean philosophy influenced later thinkers, such as Plato, who incorporated Pythagorean ideas into his own philosophical system

Number Theory Fundamentals

• Number theory is the study of the properties of integers and their relationships
• The Pythagoreans made significant contributions to the development of number theory, including:
  • The classification of numbers into even and odd
  • The concept of perfect numbers (numbers that are equal to the sum of their proper divisors)
  • The study of figurate numbers (numbers that can be represented by geometric arrangements of points)
• The Pythagoreans discovered the existence of irrational numbers, such as the square root of 2, which challenged their belief in the supremacy of whole numbers and ratios
• The Euclidean algorithm, named after the Greek mathematician Euclid, is a method for finding the greatest common divisor (GCD) of two numbers
  • The algorithm has applications in cryptography and computer science
• The fundamental theorem of arithmetic states that every positive integer greater than 1 can be uniquely represented as a product of prime numbers (up to the order of factors)
• Diophantine equations are polynomial equations with integer coefficients for which integer solutions are sought, named after the ancient Greek mathematician Diophantus

Applications in Ancient Mathematics

• The Pythagorean theorem had practical applications in ancient architecture and construction, such as in the design of right-angled triangles for building foundations and walls
• Pythagorean triples (sets of three positive integers that satisfy the Pythagorean theorem) were used in ancient surveying and land measurement
• The Pythagorean understanding of musical intervals and harmonies influenced the development of music theory in ancient Greece
  • The discovery of the mathematical basis of musical intervals led to the concept of the "music of the spheres," the idea that celestial bodies produce harmonious sounds as they move through space
• Pythagorean ideas about the mathematical nature of the universe influenced the development of ancient Greek astronomy
  • The Pythagorean concept of circular motion as the most perfect form of motion influenced the development of the geocentric model of the universe
• The Pythagorean emphasis on the study of geometry contributed to the development of ancient Greek mathematics, particularly in the work of later mathematicians such as Euclid and Archimedes

Legacy and Influence on Later Mathematics

• The Pythagorean theorem remains a fundamental concept in mathematics and has inspired numerous generalizations and extensions, such as the law of cosines and the Pythagorean theorem in higher dimensions
• Pythagorean ideas about the mathematical nature of the universe influenced the development of Western philosophy, particularly in the works of Plato and his followers
  • Plato's theory of forms and his emphasis on the study of geometry were heavily influenced by Pythagorean thought
• The Pythagorean discovery of irrational numbers led to the development of more advanced mathematical concepts, such as the real number system and the concept of mathematical proof
• The Pythagorean emphasis on the study of number theory laid the foundation for the development of modern number theory, which has applications in cryptography and computer science
• The Pythagorean school's combination of mathematics, philosophy, and mysticism influenced the development of various intellectual and spiritual traditions, such as Neoplatonism and Gnosticism

Interesting Facts and Anecdotes

• According to legend, Pythagoras discovered the mathematical basis of musical intervals when he heard the sounds produced by hammers of different weights striking an anvil
  • He realized that the intervals between the sounds corresponded to simple mathematical ratios of the weights of the hammers
• The Pythagorean school had a symbol called the tetractys, which consisted of ten points arranged in a triangular pattern
  • The tetractys represented the perfect number 10 and was used in various mystical and philosophical contexts
• Pythagoras is said to have been the first to use the term "philosopher" (lover of wisdom) to describe himself
  • He believed that the pursuit of knowledge and understanding was the highest goal of human life
• The Pythagorean theorem was known to other ancient civilizations, such as the Babylonians and the Chinese, before Pythagoras
  • However, the Pythagoreans were the first to provide a mathematical proof of the theorem
• The Pythagorean school had a strict code of secrecy, and members were forbidden from revealing the teachings of the school to outsiders
  • According to legend, a Pythagorean named Hippasus was drowned at sea for revealing the discovery of irrational numbers to the public