A Treehouse Project
Before you learn Clifford algebra you need to understand half a dozen ideas that in themselves are moderately challenging, and fascinating.
Our crazy-fun analogy envisions a huge tree with a grand treehouse in it. Math ideas are rungs on a ladder, and as you climb the ladder there are several platforms that you can rest on, as you work your way up.
Climbing the ladder is isomorphic with learning knowledge, and by the time you reach the Clifford Tree House you will know quite a bit about other stuff that is important outside of Clifford algebra.
We will want to talk about a generic operation, and when we do so we will use the symbol ♡. We’re hoping that because you’ve probably seen things like Associativity and Commutativity elsewhere, it will be deja vu.
The first platform you will reach is Sets that are closed to one or more operations.
Assume a set S with two elements, positive one and negative one, S={+1,-1}.
Let * be the operation a*b=c.
- +1*+1=+1
- +1*-1=-1
- -1*-1=+1
- -1*+1=-1
We can put any set element into a and b, and the result, c, is also a set element. After we prove this, we say that the set is closed to *.
Addition is a little more tricky. The set {1,2} is not closed to addition because 1+2=3 and 3 is not in the set.
We have to respond to tricky with clever and make the following set:
{1,2,3,…}
The above set has all positive integers. Any time you add two positive integers, you get a positive integer. Now we have a set closed to addition. Multiplication of two positive integers gives a positive integer, so the set is also closed to multiplication.
Group
A group is a set that is closed to an operation, ♡, and several rules of math are true for the elements of this group.
- Associativity — (a♡b)♡c = a♡(b♡c)
- Identity Element (e) — a♡e=a
- Inverse Element (b) — a♡b=e
Abelian Group
The next platform that we will climb to is abelian group.
An Abelian Group will have an operation, ♡, and the following will be true:
- Closure — For all a,b in the set, c=a♡b and c is in the set.
- Associativity — (a♡b)♡c = a♡(b♡c)
- Commutativity — a♡b=b♡a
- Identity Element (e) — a♡e=a
- Inverse Element (b) — a♡(b)=e
Fields
For any possible combination of two elements from the set, duplicates are allowed -and see if each of the rules below is true:
- Associativity — (a+b)+c=a+(b+c) and (a*b)*c=(a*b)*c
- Commutativity — a+b=b+a and a*b=b*a
- Identity Elements — a+0=a and a*1=a
- Inverse Elements — a+(-a) = 0 and a*(1/a)=1 [disallowing a=0]
- Distributivity of multiplication over addition — a*(b+c) = a*b + a*c
Ring
The next platform is a ring. A ring isn’t required to have multiplicative inverses or multiplicative commutativity.
It has the option of possessing either or both of these things, and if so, it gets names to indicate these additional structures.
Look at the set {…,-3,-2,-1,0,1,2,3,…}
This set wouldn’t allow multiplicative inverses.
With regard to the other exclusion, multiplicative commutativity, matrix multiplication is not commutative. Othet “things” exist which are outside of what we gave covered so far–if interested, google “endomorphism”.
We are almost two the treehouse. The next platform is an associative R-algebra.
R is a commutative ring. A is an additive Abelian group. The following is true for r in R and x,y in A:

A is unital, meaning that an element 1 exists such that for all x in A:

The last platform for the treehouse is Vector Space.
A Vector Space has a set V of vectors over a field, K. The field K provides the scalars. All the rules below are true for all a,b,c in K and all u,v,w in V.
- Addition is Associative
- Addition is Commutative
- An Identity Element for Addition exists
- Inverse Elements for Addition exist
- Compatibility of Field Multiplication with Scalar Multiplication — a(bv) = (ab)v
- A Multiplicative Identity exists
- Distributivity of scalar multiplication with respect to vector addition — a(u+v) = au + av
The Clifford Algebra Treehouse
We are now at the treehouse. There is a sign by the door: “A Clifford Algebra is a unital Associative Algebra with a vector space V over a field K and V is equipped with a Quadratic Form.”