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2025-03-01 14:15:46 UTC
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Permalinkproposed, with these multiplication rules:
(a, b) * (a', b') = (aa' + bb', ab' + a'b)
had already been studied. Since it is clearly a ring (but not a field, as
it has divisors of zero), it seemed likely to me.
And indeed, it has! This is called the set of split-complex numbers:
https://en.wikipedia.org/wiki/Split-complex_number
I came across it while watching a video by Michael Penn:
He demonstrates there that there are only three associative R-algebras
over R^2:
- Dual numbers R(epsilon) with epsilon^2 = 0 (i.e. R[X]/(X^2))
- Complex numbers R(i) with i^2 = -1 \) (i.e. R[X]/(X^2 + 1)
- Split-complex numbers R(j) with j^2 = 1 (i.e.R[X]/(X^2 - 1))
Among these three, only the complex numbers form a field. All three also
have a 2x2 matrix representation.
What should please Hachel is that split-complex numbers naturally express
Lorentz transformations, since their isometries are hyperbolic rotations.
There is even an analogue to Euler’s identity:
e^(i*theta) = cos(theta) + i*sin(theta)
which is:
e^(j*theta) = cosh(theta) + j*sinh(theta)
However, note that while R(j) corresponds to Hachel’s *first* proposed
structure, it has *nothing to do* with his *second* proposal of
introducing an element such that (i^2 = i^4 = -1 ). As was pointed out to
him (both here and on fr.sci.maths), this immediately leads to
contradictions.
It is also completely absurd to claim, as he did before shifting to
another incoherent idea (i^4 = i^2 = -1 ), that one of these three
structures would be the "correct" one while the others are "wrong".
To make a long story short, Hachel had an idea that, for once, was not
absurd. Strangely, he abandoned it in favor of another one that is
completely incoherent and contradictory.