How Imaginary Numbers Were Invented
Veritasium
23 min, 29 sec
A detailed exploration of the history and implications of imaginary numbers, from their inception in solving cubic equations to their fundamental role in modern physics.
Summary
- Mathematics evolved from quantifying the real world to solving seemingly impossible problems by inventing imaginary numbers.
- The cubic equation posed a problem for millennia until separate solutions by del Ferro and Tartaglia led to the general cubic formula.
- Imaginary numbers, once seen as useless, were crucial for solving certain cubic equations and later became fundamental in quantum mechanics.
- The Schrödinger equation, which is central to quantum physics, features imaginary numbers, indicating their essential role in describing the universe.
Chapter 1

Mathematics originated to quantify the world and tackle commerce, geography, and astronomy, leading to the challenge of solving cubic equations.
- Mathematics began as a means to quantify the world for practical purposes such as land measurement, planetary motions, and commerce.
- Cubic equations presented an 'impossible' problem that required the separation of algebra from geometry and the creation of imaginary numbers.
- Ironically, these imaginary numbers became central in the best physical theory of the universe centuries later.

Chapter 2
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Renaissance Italy's mathematics, as summarized in 'Summa de Arithmetica', faced the unsolved challenge of the cubic equation.
- Luca Pacioli, da Vinci's math teacher, published 'Summa de Arithmetica', summarizing known mathematics including the unsolved cubic equation.
- Ancient civilizations attempted to solve the cubic for over 4,000 years but failed, leading Pacioli to conclude a solution was impossible.

Chapter 3

Ancient mathematicians used geometric methods to solve quadratic equations, revealing a disconnect with negative solutions.
- Quadratic equations were solved by ancient civilizations through geometric approaches, such as completing the square.
- Mathematicians were oblivious to negative solutions as they did not have a real-world geometric interpretation.
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Chapter 4

The journey to solve the cubic equation began with Scipione del Ferro's secretive solution, leading to a mathematical duel between Fior and Tartaglia.
- Scipione del Ferro solved depressed cubics but kept his method secret for job security, later passing it to his student Fior.
- Fior's challenge to Tartaglia prompted Tartaglia to solve the depressed cubic using a geometric algorithm, which he summarized in a poem.

Chapter 5

Cardano's pursuit of Tartaglia's method led to the discovery of del Ferro's prior solution and the publication of the general cubic formula.
- Cardano, a polymath, obtained Tartaglia's method under oath not to publish it, but later found del Ferro's prior solution and published the general cubic formula.
- Cardano's 'Ars Magna' was a major mathematical achievement, pushing geometry to its limits and acknowledging Tartaglia, del Ferro, and Fior.

Chapter 6

The appearance of imaginary numbers in solving certain cubic equations led to new mathematical and geometric paradoxes.
- Complex cubic equations with real solutions sometimes produced imaginary numbers, leading to a geometric paradox involving negative areas.
- Bombelli embraced these imaginary numbers, creating a new type of number that could lead to real solutions when manipulated correctly.

Chapter 7

The 17th century saw the birth of modern mathematics with algebraic symbolism and the acceptance of imaginary numbers.
- With the development of algebraic symbolism by Viete and Descartes' use of imaginary numbers, mathematics began to detach from geometry.
- Imaginary numbers became integral to complex numbers, which are essential in the description of wave functions in physics.

Chapter 8

Imaginary numbers, once a mathematical oddity, turned out to be essential in describing the quantum world through the Schrödinger equation.
- The Schrödinger equation, featuring the square root of negative one, described quantum behavior, revolutionizing chemistry and physics.
- Despite initial resistance, imaginary numbers showed nature operates with complex numbers, a startling discovery for physicists.

Chapter 9
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Interactive learning experiences like those offered by Brilliant can deepen understanding of complex mathematical concepts.
- The video's sponsor, Brilliant, offers interactive STEM learning that aligns with the video's content, such as courses on complex numbers.
- Brilliant's approach to learning through doing can enrich one's grasp of mathematics and other STEM fields.
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