TOPICS
Search

Clifford Algebra


A Clifford algebra is an associative algebra associated with an n-dimensional vector space V over a field K and a quadratic form Q on V. In the sign convention used here, it is generated by V subject to the multiplication rule

 v^2=-Q(v)1
(1)

for every v in V, where 1 is the multiplicative identity.

More precisely, the Clifford algebra is the quotient T(V)/I(Q) of the tensor algebra T(V) by the two-sided ideal I(Q) generated by v tensor v+Q(v)1 for v in V. When the field characteristic of K is not 2, the defining rule also gives

 vw+wv=-2B(v,w)1,
(2)

where B(v,w)=[Q(v+w)-Q(v)-Q(w)]/2 is the symmetric bilinear form associated with Q.

For K=R with V an Euclidean space and Q(v)=||v||^2, an orthonormal basis e_i satisfies

e_i^2=-1
(3)
e_ie_j=-e_je_i
(4)

for i!=j. The products e_(i_1)...e_(i_k) with i_1<...<i_k, together with the empty product 1, form a vector basis of the Clifford algebra. Its dimension is therefore 2^n.

Clifford algebras are generally not commutative. When Q is identically zero, the Clifford algebra is the exterior algebra of V.

Clifford algebras are used to define spinors.

In the Wolfram Language, CliffordAlgebra represents Clifford algebras with generators whose squares are +1, -1, or 0. NonCommutativeExpand puts expressions in these algebras into canonical form.


See also

Algebra, Dirac Matrices, Exterior Algebra, Geometric Algebra, Hypercomplex Number, Quadratic Form, Quaternion, Spinor, Spinor Field, Tensor Algebra, Vector Space

Portions of this entry contributed by Todd Rowland

Explore with Wolfram|Alpha

References

Abłamowicz, R. "Hecke Algebra, SVD, and Other Computational Examples with CLIFFORD." 14 Oct 1999. https://arxiv.org/abs/math/9910069.Ablamowicz, R.; Lounesto, P.; and Parra, J. M. Clifford Algebras with Numeric and Symbolic Computations. Boston, MA: Birkhäuser, 1996.Huang, J.-S. "The Clifford Algebra." §6.2 in Lectures on Representation Theory. Singapore: World Scientific, pp. 63-65, 1999.Iyanaga, S. and Kawada, Y. (Eds.). "Clifford Algebras." §64 in Encyclopedic Dictionary of Mathematics. Cambridge, MA: MIT Press, pp. 220-222, 1980.Lawson, H. B., Jr. and Michelsohn, M.-L. Spin Geometry. Princeton, NJ: Princeton University Press, 1989.Lounesto, P. Clifford Algebras and Spinors, 2nd ed. Cambridge, England: Cambridge University Press, 2001.Lounesto, P. "Counterexamples to Theorems Published and Proved in Recent Literature on Clifford Algebras, Spinors, Spin Groups, and the Exterior Algebra." http://www.helsinki.fi/~lounesto/counterexamples.htm.Penrose, R. §11.5 in Road to Reality: A Complete Guide to the Laws of the Universe. New York: Knopf, 2004.

Referenced on Wolfram|Alpha

Clifford Algebra

Cite this as:

Weisstein, Eric W., with contributions by Todd Rowland. "Clifford Algebra." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/CliffordAlgebra.html

Subject classifications