Where's Waldo in the Standard Model?
Hello:
The newsgroup sci.physics.research was very important to me as a way of learning about physics and physics research. I began reading the posts in 1995, almost as soon as I had my first access to the Internet (using trn, if I recall correctly). As I continued to see just how much I could do with quaternions, the moderators of the newsgroup tired of me. I know one of the key players in SPR, a math guy named
John Baez, no longer thought my quest to work extensively was interesting. John was supportive of non-professionals, unless they were weasels like myself (it is an obtuse skill I have, the ability to tick of math guys). It is hugely frustrating to get a post rejected as being "overly speculative", a nice vague definition they can whip out on a whim. For the most part, I have stopped posting there.
I did make an expectation recently. This work with the cause of the 4 forces of Nature is just too cool. I was not confident they would accept it, but it got in. No one is discussing it so far, but that is par for the course. Here it is, both playful and technical. Hope you enjoy...
[Post to sci.physics.research]
Hello:
"Where's Waldo" is a cartoon phenomena whose goal is to spot Waldo somewhere in a densely drawn image. Waldo is there, you just have to work to spot him. A simple game that has meant millions for its author.
In contrast, the standard model of physics is super serious, dictating three out of the four forces of Nature: EM, the weak force, and the strong force. If you have ever seen the Lagrangian, it is densely drawn, with generators of groups, gamma matrices, binding constants, and wave functions. I do not find it enlightening.
A simpler approach to the standard model focuses on the symmetries: U(1)xSU(2)xSU(3), which are related to EM, the weak force, and the strong force respectively. The Lie algebras for these continuous groups have vector spaces with 1, 3, and 8 dimensions, which exactly matches the number of bosons involved in these forces: 1 photon for EM, +/-W, Z for the weak force, and 8 gluons for the strong force. The group U(1) has all the properties of the complex numbers with a norm of 1. The group SU(2) is the unitary quaternions, quaternions with a norm of 1. The continuous group SU(3) is also a special (norm of 1) unitary group. So now the hunt is on for these groups somewhere in EM, the weak force, or the strong force.
Although I have worked with EM, I cannot say the same for any equations involving the weak or the strong force. I have read what they do, but in an equation-free way. I cannot start with the weak or the strong force, but need to keep an eye out for them. Let's write out EM in a way Feynman called "a beautiful set of equations!" (Lectures, II, 18-11), the Maxwell equations in the Lorentz gauge:
J^u = (1/c d^2/dt^2 - c Del^2) A^u
Both J^u and A^u are 4-vectors. Quaternions can also be viewed as 4-vectors. So treat J^u and A^u as quaternions that happen to have indices (it's just a label after all, and in this case it is restricted to run from 0-3). Now that this is a quaternion wave equation, how would we write a unitary quaternion? Take the exponential of a quaternion where the scalar has been dropped:
exp(q - q*) is an element of SU(2)
There is a problem though, because the J and A have four degrees of freedom, but exp(q-q*) only has 3. We need to plug 1 degree of freedom back in. We could just grab the scalar using (q+q*), but recall the purpose of the exercise: let's go for the Abelian group U(1) since it's Lie algebra also has 1 degree of freedom. Rewrite A^u like so:
A^u = A^u/|A| exp(A^u - A*^u) = exp(A^u - A*^u) A^u/|A|
A^u commutes with itself, and with the exponential of itself because it points in the same direction so the cross product is zero (that's the non-commuting part). Together, A^u/|A| exp(A^u - A*^u) has electroweak symmetry, U(1)xSU(2)!
The Lie algebra su(3) has eight dimensions, twice the number we have in this equation. What would be a reasonable way to "double" this equation, doing some standard operation in quantum mechanics? Recall the <bra|ket> notation, which is a* b. Imagine 2 current densities, J^u and J'^v. I'd like to calculate the inner product of the two, but need a metric to do so:
g_uv J*^u J'v =
g_uv (1/c d^2/dt^2 - c Del^2)(A^u/|A| exp(A^u - A*^u))* A'^u/|A'| exp(A'^u - A'*^u)
An initial objection for this expression being a representative of U(1)xSU(2)xSU(3) might go like this. If a quaternion represents U(1)xSU(2) when written like q/|q| exp (q - q*), then the product of two quaternions should be in the same group. That's how groups work!
A detail was missed: we are taking the conjugate of one of these quaternions and multiplying it by the other. As
John Baez pointed out to me, that means that multiplication is no longer associative, since:
(a b)* c != a* (b c)
but norm ((a b)* c) = norm (a* (b c))
I happen to call this sort of non-associative multiplication "Euclidean multiplication" because the scalar part of q* q is t^2 + x^2 + y^2 + z^2. The multiplication table will necessarily be different because regular (or what I call Hamiltonian) multiplication is associative.
It is important to remember that quaternion multiplication, even Euclidean multiplication, preserves the norm. Therefore the norm of this q* q' will be one. There is still the same identity, (1, 0, 0, 0), and every quaternion will have an inverse under Euclidean multiplication. With eight numbers to plug into q* q' and a norm of 1, I believe q* q' is a way to represent SU(3).
There is a bonus to viewing this 4-vector equation as a 4-vector with the properties of an indexed quaternion, which not only can be added, subtracted and multiplied by a scalar, but also multiplied and divided with each other. The bonus is the explicit appearance of the metric g_uv. We have placed no constraints on the metric. It can be whatever, and this wave equation does not change its form. If the metric is the flat Minkowski metric, then we have the same multiplication rules set out by Hamilton for the scalar part. Calculating the inner product of two current densities will use the same equation no matter what the manifold is, whether it is static or dynamic. In terms of group theory, the equation has Diff(M) symmetry which is at the heart of general relativity.
This was a fun game of algebra, but Where's Waldo is a _visual_ exercise. It is time to translate this algebraic story into pictures. Quaternions are 4 dimensional, so how do we deal with that? Go to the movies! Imagine generating a thousand quaternions at random: different values of t, x, y, and z. Take all of them, and sort them by time t. Make an animation lasting 10 seconds, at 30 frames per second, or 300 frames total. Figure out the range of time, from earliest to latest, and divide that by 300. Any particular frame will correspond to a range of time values. If a quaternion happens to fall in the range, place it at the appropriate place given the x, y, and z values.
The software for analytic animation using quaternions has been written. Since SPR is a text based newsgroup, I'll describe the images (URL at the end if you want to see the results, but they are not trivial to grasp since we are not accustom to seeing functions of spacetime). The easiest one to deal with is SU(2) because all that needs to be done is to generate thousands of quaternions randomly, then calculate exp(q-q*), and plot the result. None of the events have a time less than zero. The norm always has to be equal to 1, so the first points start out at the extremes of +/-x, +/-y, +/-z. The image then forms a ball that shrinks to a small radius, because by that time, most of t^2+x^2+y^2+z^2=1 is the t^2 part.
When exp(q-q*) is multiplied by itself normalized, q/|q| exp(q-q*), the result is a sphere that grows and shrinks, but has a decided bias. Most of the points now have a negative time.
The animation of (q/|q| exp(q-q*))* (q'/|q'| exp(q'-q'*)) is a completely smooth rendering of spacetime from (-t,0,0,0) to (+t,0,0,0). It doesn't appear like one could devise a smoother way to fill up a volume of spacetime with events.
The take home message is simple: the symmetry of taking the inner product of two indexed quaternion 4D wave equations with a norm of one is Diff(M)xU(1)xSU(2)xSU(3). This may be the reason behind the four forces of Nature: gravity, EM, the weak force, and the strong force fill up spacetime. Way to go Waldo!
doug
http://www.theworld.com/~sweetser/quaternions/quantum/standard_model/standard_model.html
http://quaternions.sf.net/