Clifford algebras provide a unifying structure for Euclidean, Minkowski, and multivector spaces of all dimensions. Vectors and differential operators expressed in terms of Clifford algebras provide a natural language for physics which has some advantages over the standard techniques [1] - [6] . Applications of Clifford algebras and related spaces to mathematical physics are numerous. A valuable collection is given by Chishom and Common [4] . There are other applications in the literature. For example, DeFaria et al. [7] applied Clifford algebras to set up a formalism for magnetic monopoles. Salingaros [8] extended the Cauchy-Rie- mann equations of holomorphy to fields in higher-dimensional spaces in the framework of Clifford algebras and studied the Maxwell equations in vacuum and the Lorentz gauge conditions. He showed that the Maxwell equations in vacuum are equivalent to the equation of holomorphy in Minkowski space-time. Imaeda [9] showed that Maxwell equation in vacuum are equivalent to the condition of holomorphy for functions of a real biquaternion variable.

It has been shown that when the electromagnetic field is defined as the sum of an electric field vector and a magnetic field bivector, the four Maxwell equations reduce into a single equivalent equation in the domain of Pauli and Dirac algebras [3] [4] . In this work, we apply a different Clifford algebra to the Maxwell equ- ations of electromagnetism, and we show how this formulation relates to the classical theory in a straightforward manner resulting in two main formulas; the first is a simplistic rendering of Maxwell’s equations in a short formula

The second is the reconstruction of the combined electric and magnetic fields by a single transformation of the four-potential

Our investigation differs in approach from those in Hestenes and Chisholm- Common in its simplicity and ability to use a single potential function to cor- rectly derive Maxwell’s equations in a vacuum.

In what follows, we first lay out the theory of the Clifford algebra employed in this work. We then discuss its applications to electromagnetism and obtain a new electromagnetic field multivector, which is closely related to the scalar and vector potentials of the classical electromagnetics. We show that the gauge transformations of the new multivector and its potential function and the La- grangian density of the electromagnetic field are all in agreement with the transformation rules of the rank-2 antisymmetric electromagnetic field tensor. Finally, we give the matrix representation of the electromagnetic field multive- ctor and its Lorentz transformation.

Consider the Clifford algebra over the field of real numbers generated by the elements with relations

and no others [1] [10] . As a vecor space over, the algebra has dimension. A basis for consists of all products of the form, with and. The empty product is identified with the scalar 1. There are such products, and an arbitrary element of (called a multivector) is a linear combination of these products. If we write for a multiindex and, then, where for all. For instance, an arbitrary element of can be written as

An important subspace of is

which is isomorphic to the generalized Minkowski space. Notice that this is a subspace of dimension rather than dimension or.

A product where, or any expression equivalent to a scalar multiple of it is called an m-blade. Let be the sum of the m- blades of, called the m-vector part of, then

If for some positive integer m, then is said to be homogeneous of grade m.

The inner and outer products of blades are defined as follows [1] : The inner product of an r-blade and as s-blade is

The outer product of and is

By linearity, these definitions extend to and, where and are multivectors.

Some examples of inner and outer products are:

There are three important involutions on [10] :

1) inversion: defined by for

2) reversion: defined by

3) conjugation: defined by

Then it follows that, , and for all x and in.

Let be the differential operator, where. Let be the differential operator. Let be a domain in, and sup- pose that has continuous derivatives of whatever order the context requires. Then and are the left and right derivatives of, respec- tively. In terms of components, these derivatives are defined by

It is straightforward to show that the following identities hold:

The Clifford algebra maybe written as the algebra where. If we identify with the subspace spanned by, then is the usual skew-field of quater- nions with

The geometric product on satisfies the relation, where is the usual cross-product. However, since additional relations exist among, , and, inner and outer products are not defined here.

If is a vector field on, then it is straightforward to show that

Theorem 1. Suppose is a vector field on. Then if and only if, where is a real-valued harmonic function of.

Proof. A vector field equals for a real-valued function if and only if. The function is harmonic if and only if. □

In Gaussian units, the differential form of the Maxwell equations for sources in vacuum are [11]

where, , and are time-dependent vector fields in and is a real-valued function. That is, each quantity is a function of, where and is time. Note that is the charge density multiplied by and is the current density multiplied by.

We recast the Maxwell equations in the language of Clifford algebras by keeping the electric field as a vector, but replacing the magnetic field vector by the magnetic field bivector, defined as [3] [12]

The electromagnetic field multivector is then defined as. It can be shown that

In terms of and, the Maxwell equations for sources in vacuum may now be written as

Theorem 2. The Maxwell equations are equivalent to the single equation

Proof. Since,

Using the Maxwell equations, we obtain

But

Therefore, we obtain Equation (32). Conversely, assuming Equation (32), the Maxwell equations follow by setting the real parts, the vector parts, the bivector parts, and the trivector parts of each side equal. This completes the proof. □

From classical electrodynamics [11] , the fields and are derived from a scalar potential and a vector potential by

where and satisfy the wave equations

and the continuity equation

We can formulate this as follows: Let, and write

where and. Then

Note that.

The derivative of is

Using Equations (42) and (43) and noting that

we obtain

Theorem 3. The electromagnetic field is obtained from the potential function by

Proof. From Equation (46) we have. Therefore,

□

Note that Equation (47) may also be written as, since by the continuity eqation.

Recall that in classical electromagnetism the Lagrangian density in a vacuum is given by

By expanding this a bit, we find

In order to recreate this in the Clifford algebraic formulation we consider

Thus we might expect that the Lagrangian density becomes

Examining this a little we see that

Since our inner product is commutative we have a cancellation of field product terms and.

In higher dimensions, one may wish to restrict to the 0-blade so as to disallow higher dimensional cross terms. Thus we write

Now let’s consider the situation outside a vacuum. We have

Let us write

Then using our potential we have the Lagrangian density of the electro- magnetic fields outside a vacuum,

Complex numbers can be represented by matrices. Similarly, as we show in the Appendix, the Clifford algebra is represented by matrices. The element is represented by the matrix

From this we can write an natrix representation of the electromagnetic field multivector

The matrix in the upper left corner contains all the coordinates of and is the same as the matrix representation of the second-rank antisymmetric electromagnetic field tensor [11] . If we use this representation for, that is,

then the Lorentz transformation of is given by [11]

A quite lengthy calculation (see Appendix) shows that the two transformations given by Equations (54) and (73) are exactly identical.

We have shown that in the framework of the Clifford algebra defined in Equation (3), the Maxwell equations in vacuum reduce to a single equation in a fashion similar to that in other types of Clifford algebras. The multivector is closely related to the second-rank antisymmetric electromagnetic field tensor [11] , whose condition of holomorphy is also equivalent to the Maxwell equations in vacuum [8] . However, the multivector formalism may have some theoretical advantages over the tensor formalism.

Furthermore, we have shown that the electromagnetic field multivector can be derived from a potential function, which is closely related to the scalar and the vector potentials of classical electromagnetics.

Finally, we have discussed the Lorentz transformation of the potential function and the multivector field, and have shown that these transformations are in agreement with the transformation of the second-rank antisymmetric electro- magnetic field tensor.

The formulation given by other investigators [3] [4] differs from the present work in that they have employed the Pauli algebra in which the square of each of the three unit elements is +1 rather than −1, or the Dirac algebra in which one unit element has square +1 and three unit elements have square −1. All these types of Clifford algebras have been extensively used.

By repeating our calculations with instead of −1 in Equation (3), it can be shown that the Maxwell equations in vacuum reduce to, which is in agreement with the result given by Jancewicz [12] . Equation (47) then becomes, where is the potential function given by Equation (41). Equation (54) for the Lorentz transformation of then reduces to. Repeating the calculations of the Appendix, it turns out that this transformation is equivalent to, where the matrix represen- tation of is now given by

Note that this matrix is not antisymmetric and the representation is not the same as that of the electromagnetic field tensor, and the transformation rule is also different. This is in contrast to the result obtained from applying a Clifford algebra with.

Mohazzabi, P., Wielenberg, N.J. and Alexander, G.C. (2017) A New Formulation of Maxwell’s Equations in Clifford Algebra. Journal of Applied Mathematics and Physics, 5, 1575-1588. https://doi.org/10.4236/jamp.2017.58130

Here we show that the two transformations given in Equations (54) and (73) are identical.

We have

and

Therefore,

It follows that the matrix representation of is

We also have

So the matrix representation of is

The general Lorentz transformation and its inverse are given by the following matrices:

From Equation (54) we have

where

and

Let be the m-th row of. Then

and

Recall that from Equation (42) we have

and from Equation (37) we have

Therefore,

Then we find the following identity by carrying out the multiplication,

For example, with and we obtain the Lorentz transform of,

and with and we obtain

It is now straightforward to show that the identity in Equation (18) is identical to

where is the transpose of the general Lorentz transformation matrix, and is the electromagnetic field tensor given by Equation (72).

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