Sedenion

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. The set of sedenions is denoted by .

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#Fano plane mnemonic,[1] showing the 35 triads as hyperplanes through the Real (e0) 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 , the power is well defined. They are also flexible.

Every sedenion is a linear combination of the unit sedenions e0, e1, e2, e3, ...,e15, which form a basis of the vector space of sedenions. Every sedenion can be represented in the form

.

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 (e0 to e7 in the table below), and therefore also the quaternions (e0 to e3), complex numbers (e0 and e1) and reals (e0).

The sedenions have a multiplicative identity element e0 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 (e3 + e10)×(e6 − e15). All hypercomplex number systems after sedenions that are based on the Cayley–Dickson construction contain zero divisors.

The multiplication table of these unit sedenions follows:

 ×  e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 e13 e14 e15
e0 e0 e1 e2 e3 e4 e5 e6 e7 e8 e9 e10 e11 e12 e13 e14 e15
e1 e1 −e0 e3 −e2 e5 −e4 −e7 e6 e9 −e8 −e11 e10 −e13 e12 e15 −e14
e2 e2 −e3 −e0 e1 e6 e7 −e4 −e5 e10 e11 −e8 −e9 −e14 −e15 e12 e13
e3 e3 e2 −e1 −e0 e7 −e6 e5 −e4 e11 −e10 e9 −e8 −e15 e14 −e13 e12
e4 e4 −e5 −e6 −e7 −e0 e1 e2 e3 e12 e13 e14 e15 −e8 −e9 −e10 −e11
e5 e5 e4 −e7 e6 −e1 −e0 −e3 e2 e13 −e12 e15 −e14 e9 −e8 e11 −e10
e6 e6 e7 e4 −e5 −e2 e3 −e0 −e1 e14 −e15 −e12 e13 e10 −e11 −e8 e9
e7 e7 −e6 e5 e4 −e3 −e2 e1 −e0 e15 e14 −e13 −e12 e11 e10 −e9 −e8
e8 e8 −e9 −e10 −e11 −e12 −e13 −e14 −e15 −e0 e1 e2 e3 e4 e5 e6 e7
e9 e9 e8 −e11 e10 −e13 e12 e15 −e14 −e1 −e0 −e3 e2 −e5 e4 e7 −e6
e10 e10 e11 e8 −e9 −e14 −e15 e12 e13 −e2 e3 −e0 −e1 −e6 −e7 e4 e5
e11 e11 −e10 e9 e8 −e15 e14 −e13 e12 −e3 −e2 e1 −e0 −e7 e6 −e5 e4
e12 e12 e13 e14 e15 e8 −e9 −e10 −e11 −e4 e5 e6 e7 −e0 −e1 −e2 −e3
e13 e13 −e12 e15 −e14 e9 e8 e11 −e10 −e5 −e4 e7 −e6 e1 −e0 e3 −e2
e14 e14 −e15 −e12 e13 e10 −e11 e8 e9 −e6 −e7 −e4 e5 e2 −e3 −e0 e1
e15 e15 e14 −e13 −e12 e11 e10 −e9 e8 −e7 e6 −e5 −e4 e3 e2 −e1 −e0

From the above table, we can see that:

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

{​{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 {ea, eb, ec, ed}, where (ea + eb)(ec + ed)=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

Notes

  1. ↑ (Baez 2002, p. 6)

References

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