Sedenion

Sedenions
Symbol	$\mathbb {S}$
Type	nonassociative algebra
Units	e0...e15
Multiplicative identity	e0
Main properties	power associativity distributivity
Common systems
$\mathbb {N}$ Natural numbers $\mathbb {Z}$ Integers $\mathbb {Q}$ Rational numbers $\mathbb {R}$ Real numbers $\mathbb {C}$ Complex numbers $\mathbb {H}$ Quaternions Less common systems $\mathbb {O}$ Octonions $\mathbb {S}$ Sedenions $\mathbb {T}$ Trigintaduonions

In abstract algebra, the sedenions form a 16-dimensional noncommutative and nonassociative algebra over the reals obtained by applying the Cayley–Dickson construction to the octonions. Unlike the octonions, the sedenions are not an alternative algebra. It is possible to apply the Cayley-Dickson construction to the sedenions infinitely on, but the algebras created have the same properties as sedenions and are of little interest.

The term sedenion is also used for other 16-dimensional algebraic structures, such as a tensor product of two copies of the biquaternions, or the algebra of 4 by 4 matrices over the reals, or that studied by Smith (1995).

Arithmetic

A visualization of a 4D extension to the cubic octonion, showing the 35 triads as hyperplanes through the real $(e_{0})$ vertex of the sedenion example given.

Like octonions, multiplication of sedenions is neither commutative nor associative. But in contrast to the octonions, the sedenions do not even have the property of being alternative. They do, however, have the property of power associativity, which can be stated as that, for any element x of $\mathbb {S}$, the power $x^{n}$ is well defined. They are also flexible.

Every sedenion is a linear combination of the unit sedenions $e_{0}$, $e_{1}$, $e_{2}$, $e_{3}$, ...,$e_{15}$, which form a basis of the vector space of sedenions. Every sedenion can be represented in the form

$x=x_{0}e_{0}+x_{1}e_{1}+x_{2}e_{2}+\ldots +x_{14}e_{14}+x_{15}e_{15},\,$.

Addition and subtraction are defined by the addition and subtraction of corresponding coefficients and multiplication is distributive over addition.

Like other algebras based on the Cayley–Dickson construction, the sedenions contain the algebra they were constructed from. So, they contain the octonions ($e_{0}$ to $e_{7}$ in the table below), and therefore also the quaternions ($e_{0}$ to $e_{3}$), complex numbers ($e_{0}$ and $e_{1}$) and reals ($e_{0}$).

The sedenions have a multiplicative identity element $e_{0}$ and multiplicative inverses but they are not a division algebra because they have zero divisors. This means that two non-zero sedenions can be multiplied to obtain zero: an example is ($e_{3}$ + $e_{10}$)($e_{6}$ − $e_{15}$). All hypercomplex number systems after sedenions that are based on the Cayley–Dickson construction contain zero divisors.

Sedenion multiplication table

		multiplier $e_{j}$
	$e_{i}e_{j}$	$e_{0}$	$e_{1}$	$e_{2}$	$e_{3}$	$e_{4}$	$e_{5}$	$e_{6}$	$e_{7}$	$e_{8}$	$e_{9}$	$e_{10}$	$e_{11}$	$e_{12}$	$e_{13}$	$e_{14}$	$e_{15}$
multiplicand $e_{i}$	$e_{0}$	$e_{0}$	$e_{1}$	$e_{2}$	$e_{3}$	$e_{4}$	$e_{5}$	$e_{6}$	$e_{7}$	$e_{8}$	$e_{9}$	$e_{10}$	$e_{11}$	$e_{12}$	$e_{13}$	$e_{14}$	$e_{15}$
	$e_{1}$	$e_{1}$	−$e_{0}$	$e_{3}$	−$e_{2}$	$e_{5}$	−$e_{4}$	−$e_{7}$	$e_{6}$	$e_{9}$	−$e_{8}$	−$e_{11}$	$e_{10}$	−$e_{13}$	$e_{12}$	$e_{15}$	−$e_{14}$
	$e_{2}$	$e_{2}$	−$e_{3}$	−$e_{0}$	$e_{1}$	$e_{6}$	$e_{7}$	−$e_{4}$	−$e_{5}$	$e_{10}$	$e_{11}$	−$e_{8}$	−$e_{9}$	−$e_{14}$	−$e_{15}$	$e_{12}$	$e_{13}$
	$e_{3}$	$e_{3}$	$e_{2}$	−$e_{1}$	−$e_{0}$	$e_{7}$	−$e_{6}$	$e_{5}$	−$e_{4}$	$e_{11}$	−$e_{10}$	$e_{9}$	−$e_{8}$	−$e_{15}$	$e_{14}$	−$e_{13}$	$e_{12}$
	$e_{4}$	$e_{4}$	−$e_{5}$	−$e_{6}$	−$e_{7}$	−$e_{0}$	$e_{1}$	$e_{2}$	$e_{3}$	$e_{12}$	$e_{13}$	$e_{14}$	$e_{15}$	−$e_{8}$	−$e_{9}$	−$e_{10}$	−$e_{11}$
	$e_{5}$	$e_{5}$	$e_{4}$	−$e_{7}$	$e_{6}$	−$e_{1}$	−$e_{0}$	−$e_{3}$	$e_{2}$	$e_{13}$	−$e_{12}$	$e_{15}$	−$e_{14}$	$e_{9}$	−$e_{8}$	$e_{11}$	−$e_{10}$
	$e_{6}$	$e_{6}$	$e_{7}$	$e_{4}$	−$e_{5}$	−$e_{2}$	$e_{3}$	−$e_{0}$	−$e_{1}$	$e_{14}$	−$e_{15}$	−$e_{12}$	$e_{13}$	$e_{10}$	−$e_{11}$	−$e_{8}$	$e_{9}$
	$e_{7}$	$e_{7}$	−$e_{6}$	$e_{5}$	$e_{4}$	−$e_{3}$	−$e_{2}$	$e_{1}$	−$e_{0}$	$e_{15}$	$e_{14}$	−$e_{13}$	−$e_{12}$	$e_{11}$	$e_{10}$	−$e_{9}$	−$e_{8}$
	$e_{8}$	$e_{8}$	−$e_{9}$	−$e_{10}$	−$e_{11}$	−$e_{12}$	−$e_{13}$	−$e_{14}$	−$e_{15}$	−$e_{0}$	$e_{1}$	$e_{2}$	$e_{3}$	$e_{4}$	$e_{5}$	$e_{6}$	$e_{7}$
	$e_{9}$	$e_{9}$	$e_{8}$	−$e_{11}$	$e_{10}$	−$e_{13}$	$e_{12}$	$e_{15}$	−$e_{14}$	−$e_{1}$	−$e_{0}$	−$e_{3}$	$e_{2}$	−$e_{5}$	$e_{4}$	$e_{7}$	−$e_{6}$
	$e_{10}$	$e_{10}$	$e_{11}$	$e_{8}$	−$e_{9}$	−$e_{14}$	−$e_{15}$	$e_{12}$	$e_{13}$	−$e_{2}$	$e_{3}$	−$e_{0}$	−$e_{1}$	−$e_{6}$	−$e_{7}$	$e_{4}$	$e_{5}$
	$e_{11}$	$e_{11}$	−$e_{10}$	$e_{9}$	$e_{8}$	−$e_{15}$	$e_{14}$	−$e_{13}$	$e_{12}$	−$e_{3}$	−$e_{2}$	$e_{1}$	−$e_{0}$	−$e_{7}$	$e_{6}$	−$e_{5}$	$e_{4}$
	$e_{12}$	$e_{12}$	$e_{13}$	$e_{14}$	$e_{15}$	$e_{8}$	−$e_{9}$	−$e_{10}$	−$e_{11}$	−$e_{4}$	$e_{5}$	$e_{6}$	$e_{7}$	−$e_{0}$	−$e_{1}$	−$e_{2}$	−$e_{3}$
	$e_{13}$	$e_{13}$	−$e_{12}$	$e_{15}$	−$e_{14}$	$e_{9}$	$e_{8}$	$e_{11}$	−$e_{10}$	−$e_{5}$	−$e_{4}$	$e_{7}$	−$e_{6}$	$e_{1}$	−$e_{0}$	$e_{3}$	−$e_{2}$
	$e_{14}$	$e_{14}$	−$e_{15}$	−$e_{12}$	$e_{13}$	$e_{10}$	−$e_{11}$	$e_{8}$	$e_{9}$	−$e_{6}$	−$e_{7}$	−$e_{4}$	$e_{5}$	$e_{2}$	−$e_{3}$	−$e_{0}$	$e_{1}$
	$e_{15}$	$e_{15}$	$e_{14}$	−$e_{13}$	−$e_{12}$	$e_{11}$	$e_{10}$	−$e_{9}$	$e_{8}$	−$e_{7}$	$e_{6}$	−$e_{5}$	−$e_{4}$	$e_{3}$	$e_{2}$	−$e_{1}$	−$e_{0}$

Sedenion properties

From the above table, we can see that:

$e_{0}e_{i}=e_{i}e_{0}=e_{i},$

$e_{i}e_{i}=-e_{0}\,\,{\text{for}}\,\,i\neq 0,$

$e_{i}e_{j}=-e_{j}e_{i}\,\,{\text{for}}\,\,i\neq j\,\,{\text{and}}\,\,i,j\neq 0.$

Anti-associative

The sedenions are NOT fully anti-associative. Choose any four generators, $i,j,k$ and $l$. The following 5-cycle shows that at least one of these relations must associate.

$(ij)(kl)=-((ij)k)l=(i(jk))l=-i((jk)l)=i(j(kl))=-(ij)(kl)=0$

In particular, in the table above, using $e_{1},e_{2},e_{4}$ and $e_{8}$ the last expression associates. $(e_{1}e_{2})e_{12}=e_{1}(e_{2}e_{12})=-e_{15}$

Quaternionic subalgebras

The 35 triads that make up this specific sedenion multiplication table with the 7 triads of the octonions used in creating the sedenion through the Cayley–Dickson construction shown in bold red:

The binary representations of the indices of these triples xor to 0.

{​{1, 2, 3} , {1, 4, 5} , {1, 7, 6} , {1, 8, 9}, {1, 11, 10}, {1, 13, 12}, {1, 14, 15},
{2, 4, 6} , {2, 5, 7} , {2, 8, 10}, {2, 9, 11}, {2, 14, 12}, {2, 15, 13}, {3, 4, 7} ,
{3, 6, 5} , {3, 8, 11}, {3, 10, 9}, {3, 13, 14}, {3, 15, 12}, {4, 8, 12}, {4, 9, 13},
{4, 10, 14}, {4, 11, 15}, {5, 8, 13}, {5, 10, 15}, {5, 12, 9}, {5, 14, 11}, {6, 8, 14},
{6, 11, 13}, {6, 12, 10}, {6, 15, 9}, {7, 8, 15}, {7, 9, 14}, {7, 12, 11}, {7, 13, 10}​}

The list of 84 sets of zero divisors {$e_{a}$, $e_{b}$, $e_{c}$, $e_{d}$}, where ($e_{a}$ + $e_{b}$)$\circ$($e_{c}$ + $e_{d}$)=0:

Applications

Moreno (1998) showed that the space of pairs of norm-one sedenions that multiply to zero is homeomorphic to the compact form of the exceptional Lie group G₂. (Note that in his paper, a "zero divisor" means a pair of elements that multiply to zero.)

See also

• Pfister's sixteen-square identity
• Hypercomplex number
• Split-complex number

References

• Imaeda, K.; Imaeda, M. (2000), "Sedenions: algebra and analysis", Applied Mathematics and Computation, 115 (2): 77–88, doi:10.1016/S0096-3003(99)00140-X, MR 1786945
• Baez, John C. (2002). "The Octonions". Bulletin of the American Mathematical Society. New Series. 39 (2): 145–205. arXiv:math/0105155v4. Bibcode:1994BAMaS..30..205W. doi:10.1090/S0273-0979-01-00934-X. MR 1886087. {{cite journal}}: Invalid |ref=harv (help)
• Kinyon, M.K.; Phillips, J.D.; Vojtěchovský, P. (2007). "C-loops: Extensions and constructions". Journal of Algebra and its Applications. 6 (1): 1–20. arXiv:math/0412390. CiteSeerX 10.1.1.240.6208. doi:10.1142/S0219498807001990.
• Kivunge, Benard M.; Smith, Jonathan D. H (2004). "Subloops of sedenions" (PDF). Comment. Math. Univ. Carolinae. 45 (2): 295–302.
• Moreno, Guillermo (1998), "The zero divisors of the Cayley–Dickson algebras over the real numbers", Bol. Soc. Mat. Mexicana, Series 3, 4 (1): 13–28, arXiv:q-alg/9710013, Bibcode:1997q.alg....10013G, MR 1625585
• Smith, Jonathan D. H. (1995), "A left loop on the 15-sphere", Journal of Algebra, 176 (1): 128–138, doi:10.1006/jabr.1995.1237, MR 1345298