Combining ‘i’ and Infinity: Exploring Complex Numbers at the Infinite Horizon

Lucas Potrykus
ILLUMINATION
Published in
3 min readJul 31, 2023
Photo by Robert Wiedemann on Unsplash

In mathematics, the combination of the imaginary unit ‘i’ and infinity leads us into a seriously fascinating realm where complex numbers extend their reach beyond finite boundaries. Complex numbers, comprising a real part and an imaginary part, are essential in solving various mathematical problems and have found extensive applications in engineering, physics, and other scientific disciplines. Of course, we must remember that infinity is a concept NOT a number. So, let’s get into it.

Complex Numbers: A Brief Overview

Before we dive into the combination of ‘i’ and infinity, let’s review the fundamentals of complex numbers (see this as a warm-up before a Champions Leaguefinal). A complex number is expressed in the form a+bi, where a and b are real numbers, and ‘i’ represents the imaginary unit defined as i² = −1. The real part of the complex number is a, and the imaginary part is bi. Complex numbers are represented in the complex plane, with the real axis corresponding to the real part and the imaginary axis corresponding to the imaginary part. Ok, there we go, you’re all up to speed.

Infinity in the Complex Plane

In the complex plane, infinity is not a single point but rather a concept (as I’ve already mentioned) that represents the behavior of complex numbers as they approach unbounded values. We often refer to infinity as a “point at infinity,” which is not located at a specific spot but is rather an “asymptote” (go on, look that word up!) that all complex numbers converge to as their magnitudes grow without bound.

Kidding, asymptote = a straight line that continually approaches a given curve but does not meet it at any finite distance. (from google so trust it)

To describe infinity in the complex plane, we use the Riemann (He’s everywhere at this point) sphere, which is a one-point compactification of the complex plane. In this representation, the complex plane is extended to include a point at infinity, forming a sphere. Complex infinity is depicted as the “north pole” of the Riemann sphere.

Complex Infinity Arithmetic

One fascinating aspect of combining ‘i’ and infinity lies in the arithmetic involving complex infinity. When we perform operations like addition, subtraction, multiplication, or division with infinity, the results can lead to intriguing outcomes.

For example, consider the expression z = 1/0​ where z represents the division of 1 by zero. In real arithmetic, this operation is undefined. However, in the realm of complex numbers, the result is complex infinity, represented as z = ∞.

Similarly, when we evaluate the expression w = ∞/1​, the result is zero. This demonstrates the concept of how dividing a finite number by an infinitely large number approaches zero.

Complex Infinity in Limit Analysis

Complex infinity also plays a significant role in limit analysis. When evaluating limits of complex functions, the behavior of these functions near singularities or points at infinity can be critical in understanding their overall behavior.

For instance, as z approaches complex infinity in the function f(z) = 1/z​, the function tends towards zero. This concept is instrumental in the study of meromorphic functions and their poles. Actually not that complicated was it..?

Done!

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