Here is some more good information, thanks to Florin Moldoveanu
The best place for the beginning of the answer is Baez's Octonion paper:
http://math.ucr.edu/home/baez/octonions/ Reals, complex, quaternions, octonions, sedenions obey the Cayley-Dickson construction
http://math.ucr.edu/home/baez/octonions/node5.htmlClifford algebras obey the relation:
vw + wv = -2<v,w>
http://math.ucr.edu/home/baez/octonions/node6.htmlwhich by the polarization identity:
< x, y> = 1/ (|| x+y||^2 - || x||^2 - || y||^2)
becomes:
v^2 = -||v||^2
Clifford algebras are associative, octonions are not. (in the Cayley-Dickson, after complex numbers, at every step the next algebra loses some property: quaternions are not commutative, octonios are not commutative or associative.
For Cl(0,3) see the appendix in
http://arxiv.org/pdf/1109.0535v3.pdf To compute in it is very easy: use the following simple rules (e1,e2,e3 are not commutative):
e1e1 = e2e2 = e3e3 = 1
and
e1e2 = −e2e1, e1e3 = −e3e1, e2e3 = −e3e2
and remember the basis:
1, - scalar
e1,e2,e3, - vectors
e1e2, e3e1,e2e3 - bivectors
e1e2e3 - pseudo-scalar
The relation with S^7 comes from Hopf fibration remembering that Cayley-Dickson generates the only normed division number systems and this is related with projective planes because of the division property, but this is an entire different large topic.
The theory of parallelizable spheres is related to Hopf fibration which is a large topic. The key idea is like this: in the most general setting, have 2 groups A and C and perform a Cartesian product AxC If you understand C as an equivalence class, this is related with short exact sequences
http://mathworld.wolfram.com/ShortExactSequence.html0->A->AxC->C->0 and C ~ AxC/C
[ An exact sequence is a chain of functions where the image of a function is the ker of the next function and this generalizes the idea that "the boundary of a boundary is zero" in topology. Exact sequences are used in homology and cohomology theory (algebraic topology). A short exact sequence is a short "exact sequence" of 3 spaces sandwiched between null spaces. The null spaces means that the A->AxC function is injective, and the AxC->C function is surjective and sometimes the null spaces are omitted.]
Now in general in a short exact sequence: 0->A->B->C->0 B *IS NOT NECESSARILY ONLY* AxC and given A and C they do not define B uniquely and the problem is to classify all possible B's. Another way to understand B is as a fibre bundle (
http://en.wikipedia.org/wiki/Fiber_bundle A=the fiber space, C = the base space, B=the entire space).
A Hopf fibration (
http://en.wikipedia.org/wiki/Hopf_fibration) for S3 is a short exact sequence:
0->S1->S3->S2->0
and for S7:
0->S3->S7->S4->0
Now since S3 is not S1xS2, the fibers interlock (when B=/=AxC the fibers twist around one another)
Joy is using the theory of paralellized spheres to get a norm factorization: ||ab||=||a|| ||b|| property which allows him to claim the lack of superposition (in QM Bell states are not separable like this) in his model.