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Penumbra's Notebook


At the edge of light and shadow, ideas take shape.


  • March 9, 2026

    The Algebra’s Apprentice: Prelude – Part II


    In The Algebra’s Apprentice: Prelude – Part I, I shared how my initial approach to learning about physics changed from one of awe and reverence to skeptical inquiry. This is the latter half of the prelude, wherein I will tell you the story of how I came to meet a most mysterious algebra. A Shape… Continue reading →

    The Algebra’s Apprentice
    closure, Hamilton quaternions, hyperbolic quaternions, idempotents, left/right multiplication, Lie algebras, Lorentz group, nonassociative algebra, special relativity, The Algebra’s Apprentice
  • March 8, 2026

    The Algebra’s Apprentice: Prelude – Part I


    In “The Algebra’s Apprentice” posts I begin writing here, I intend to faithfully tell the story of how I met Macfarlane’s algebra and the journey I have been on ever since. This is an ongoing work in progress, a way to share the narrative arc of a still unfolding exploration. A Quantum of Curiosity That… Continue reading →

    The Algebra’s Apprentice
    The Algebra’s Apprentice
  • February 3, 2026

    On the Insufficiency of Groupoids


    Macfarlane’s hyperbolic quaternions are the source of unresolved mystery yet again. Idempotents play havoc with invertibility and give groupoids the boot. Continue reading →

    Research Notes
    groupoids, hyperbolic quaternions, idempotents, nonassociative algebra
  • December 29, 2025

    The Emperor’s New Closure


    This playful notebook entry is a story that came to mind after a very real algebraic surprise I ran into while working with matrix representations. Posh Properties There once was an algebra that loved to try on matrix representations. It seemed of a reasonable and regal character, governing by simple laws and properties. While the… Continue reading →

    Yoneda’s Bane
    closure, idempotents, math humor, nonassociativity, representation
  • December 29, 2025

    Closure Note


    Definition Reminder A hyperbolic quaternion (Macfarlane non-associative variety) is a linear combination of the elements \(\lbrace 1, i, j, k \rbrace\) using real coefficients such that \[q = q^0 1 + q^1 i + q^2 j + q^3 k, \quad q^0, q^1, q^2, q^3 \in \Re. \] Multiplication is defined according to the following rules:… Continue reading →

    Research Notes
    closure, Hamilton quaternions, hyperbolic quaternions, left/right multiplication
  • November 26, 2025

    The Compass and the Gyre


    The Compass and the Gyre

    When gyrovector spaces and hyperbolic quaternions brush against one another, their shared symmetries shimmer — and richer geometric structures stir just beneath the surface. Continue reading →

    Expository Essays
    gyrovector spaces, hyperbolic geometry, hyperbolic quaternions, Lie algebras, Lorentz group, nonassociative algebra, special relativity, Thomas precession
  • October 22, 2025

    Hyperbolic Quaternions


    Hyperbolic Quaternions

    An introduction to Macfarlane’s hyperbolic quaternions, a quaternionic algebra whose chiral multiplication reveals a direct basis for the Lorentz generators. A primer on their structure, pathologies, and connection to spacetime symmetries. Continue reading →

    Expository Essays
    geometric algebra, hyperbolic quaternions, left/right multiplication, Lie algebras, Lorentz group, nonassociative algebra, spacetime, special relativity, symmetry

Categories

  • Expository Essays
  • Research Notes
  • The Algebra's Apprentice
  • Yoneda's Bane

Recent Posts

  • The Algebra’s Apprentice: Prelude – Part II
  • The Algebra’s Apprentice: Prelude – Part I
  • On the Insufficiency of Groupoids
  • The Emperor’s New Closure
  • Closure Note


 

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