Masteries · Jason GlowneyArithmoí Book 1

Masteries

1.6.1 The Singularity

At the end of Chap­ter 5 we touched upon the sphere of tan­gent spaces as the sin­gu­lar­i­ty sit­u­at­ed at the origin ∈ℂ3\in \mathbb{C}^{3} space. In math­e­mat­ics, the term sin­gu­lar­i­ty de­notes a point where a given math­e­mat­i­cal object, such as an equa­tion or a sur­face, is not de­fined or ceases to be well-be­haved in the an­a­lyt­ic sense.1 As an in­di­vid­ual math­e­mat­i­cal object, the in­fi­nite sphere of tan­gent spaces 𝔗(S3ℂ∞)\mathfrak{T}\left( S_{3\mathbb{C}}^{\infty} \right) is con­tin­u­ous and well-be­haved, as shown in the last chap­ter, and would not fit the math­e­mat­i­cal de­f­i­n­i­tion of a sin­gu­lar­i­ty in this regard. We use the term sin­gu­lar­i­ty mind­ful of the per­spec­tive from which it is being an­a­lyzed, and when using real analy­sis, this would meet the cri­te­ria for a math­e­mat­i­cal sin­gu­lar­i­ty. To demon­strate this point, we can take the func­tion f(x)=1x2−1, x∈ℝf(x) = \frac{1}{x^{2} - 1},\ x\in \mathbb{R}, and plot this in the Carte­sian plane, where it is read­i­ly seen, for x=±1x = \pm 1, the func­tion goes to in­fin­i­ty (Figure 1.6.1.a), for xx on the in­ter­val [−1.5,1.5]\lbrack - 1.5,1.5\rbrack.

Figure 1.6.1 –a: f(x)=1x2−1, x∈ℝ, x=[−1.5,1.5]f(x) = \frac{1}{x^{2} - 1},\ x\in \mathbb{R},\ x = \lbrack - 1.5,1.5\rbrack on the left, and b: x∈Imag, x=[−1.5,1.5]x \in Imag,\ x = \lbrack - 1.5,1.5\rbrack on the right.

By taking the same func­tion for xx as imag­i­nary-valued, we find the com­plete­ly dif­fer­ent result of a con­tin­u­ous curve, with­out the sin­gu­lar poles for the real-valued func­tion, as seen above in Figure 1.6.1.b. A sur­face plot of the func­tion f(x)=|1X2−1|f(x) = \left| \frac{1}{X^{2} - 1} \right|, for X=(x+ix), x∈ℝX = (x + ix),\ x\in \mathbb{R}, as a com­bi­na­tion of the real and imag­i­nary func­tion com­po­nents, re­veals the con­tin­u­ous func­tion plot­ted in Figure 1.6.2.

Figure
Figure 1.6.2 – f(x)=|1X2−1|, X=(x+ix),x∈ℝf(x) = \left| \frac{1}{X^{2} - 1} \right|,\ X = (x + ix),x\in \mathbb{R}

By the de­f­i­n­i­tion, for x∈ℝx\in \mathbb{R} , the func­tion f(x)=|1X2−1|f(x) = \left| \frac{1}{X^{2} - 1} \right|admits no real so­lu­tions for xx, in its de­nom­i­na­tor, when solved for zero

(x+ix)2−1=0,\begin{array}{r} (x + ix)^{2} - 1 = 0, \end{array}
(1.6.1)

which re­strains the func­tion from going off to in­fin­i­ty. For x∈ℂx\in \mathbb{C}, in the above, we could choose x=(−12+i2)x = \left( - \frac{1}{2} + \frac{i}{2} \right), or (12−i2)\left( \frac{1}{2} - \frac{i}{2} \right) to find, once again, sin­gu­lar­i­ties lurk­ing in the func­tion. The case in point, the func­tion f(z)=1z2−1,f(z) = \frac{1}{z^{2} - 1},for z=(x+iy),z = (x + iy), x,y∈ℝx,y\in \mathbb{R}, has sin­gu­lar­i­ties which form on its sur­face for y=(ix−i),(ix+i)y = (ix - i),(ix + i), and x=(−1−iy),(1−iy)x = ( - 1 - iy),(1 - iy), seen in Figure 1.6.3, below.

Figure 1.6.3 – f(z)=1z2−1, for z=(x+iy),x,y∈ℝf(z) = \frac{1}{z^{2} - 1},\ for\ z = (x + iy),x,y\in \mathbb{R}, real-valued on the left, and imag­i­nary-valued on the right.

We con­sid­er a sim­i­lar con­cept for the D3/S3D_{3}/S_{3} group, a sub­group ⊂S3ℂ∞\subset S_{3\mathbb{C}}^{\infty}, and if our per­spec­tive was con­fined to the real num­bers, rep­re­sen­ta­tive of the dis­joint hy­per­bo­lae in the X1,X2,X3X_{1},X_{2},X_{3}-planes, it would appear as dis­con­nect­ed for ab­solute number values <1< 1 (Figure 1.6.4).

Figure
Figure 1.6.4 – The D3/S3D_{3}/S_{3} hy­per­bo­lae ∈ℝ\in \mathbb{R}.

From the per­spec­tive of ℂ3\mathbb{C}^{3} and the S3ℂ∞S_{3\mathbb{C}}^{\infty} group, we know that the hy­per­bo­lae are not dis­con­nect­ed, when taken in the con­text of their Lie al­ge­bra sub­group rep­re­sen­ta­tion, and on the sur­face of the con­tin­u­ous sphere of tan­gent spaces group ∈ℂ3\in \mathbb{C}^{3}.

  1. "The De­fin­i­tive Glos­sary of Higher Math­e­mat­i­cal Jargon — Sin­gu­lar­i­ty". Math Vault. 2019-08-01.