Why were complex numbers introduced in physics?

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Discussion Overview

The discussion centers around the introduction of complex numbers in physics, particularly in the context of analyzing AC circuits, including concepts like voltage, current, and impedance. Participants explore the mathematical necessity and implications of using complex numbers, as well as their relevance to physical phenomena.

Discussion Character

  • Exploratory
  • Debate/contested
  • Mathematical reasoning
  • Conceptual clarification

Main Points Raised

  • Some participants propose that complex numbers were introduced due to the limitations of real numbers, particularly in solving equations like x² + 1 = 0, which have no real solutions.
  • Others argue that the use of complex numbers in AC circuit analysis is primarily a mathematical convenience, allowing for simpler calculations using exponential forms rather than trigonometric functions.
  • A participant questions the necessity of solving equations with complex solutions, suggesting that it may not relate directly to natural phenomena.
  • Some participants note that while complex numbers are seen as a mathematical tool, they find applications beyond AC circuits, such as in aerodynamics and fluid mechanics.
  • There is a discussion about whether complex numbers serve as a faithful model of reality or merely as a mathematical shorthand, with differing opinions on their role in physics.
  • A participant mentions that while physical processes can often be described using real numbers, there are many non-physical equations that only have complex solutions.
  • Some participants draw parallels between complex numbers and other mathematical constructs, like irrational numbers, questioning the necessity of each in modeling reality.
  • There is a suggestion that complex numbers can be viewed as points in a two-dimensional plane, raising questions about their relevance to real-world applications.

Areas of Agreement / Disagreement

Participants express a range of views on the necessity and role of complex numbers in physics, with no clear consensus on whether they are a fundamental aspect of modeling reality or simply a mathematical convenience. The discussion remains unresolved regarding the implications of using complex numbers versus real numbers in various contexts.

Contextual Notes

Participants highlight the limitations of real numbers in certain equations and the potential for complex numbers to simplify mathematical operations. However, the discussion also reveals uncertainty about the relationship between mathematical constructs and their applicability to physical phenomena.

  • #31
To me, it helps that one of the first things one learns in complex analysis is that a complex number is nothing more than an ordered pair (which can also be represented by a + bi). They're just ordered pairs that we know how to do operations with. Or from a physics viewpoint, it's almost like a unit vector that points upwards (with the exception of that little i^2 = -1 thing) if we assume that a number not multiplied by i points horizontally.
 
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  • #32
Complex numbers weren't invented with any specific application in mind. They were introduced to solve certain equations which had no real solutions. The fact that they are useful in physics was , I reckon, a coincidence. They weren't designed to be that way.
 
  • #33
I recommend a very entertaining book An Imaginary Tale: The Story of i [the square root of minus one] By Paul J. Nahin

The science and math communities resisted the need for complex numbers for centuries. They had the same question as the OP. The book tells the story of how they were eventually persuaded.

Another book, QED: The Strange Theory of Light and Matter By Richard Feynman explains quantum mechanics using very clever graphics instead of complex numbers. Indeed instead of any number or equations. Studying Feynman's graphics makes it obvious that quantum mechanics can never be correctly described by just real arithmetic. Both the magnitude and phase are mandatory to get the correct answers.
 

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