Bivector (complex)

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In mathematics, a bivector is the vector part of a biquaternion. For biquaternion q = w + xi + yj + zk, w is called the biscalar and xi + yj + zk is its bivector part. The coordinates w, x, y, z are complex numbers with imaginary unit h:

A bivector may be written as the sum of real and imaginary parts:

where and are vectors. Thus the bivector [1]

The Lie algebra of the Lorentz group is expressed by bivectors. In particular, if r1 and r2 are right versors so that , then the biquaternion curve {exp θr1 : θR} traces over and over the unit circle in the plane {x + yr1 : x, yR}. Such a circle corresponds to the space rotation parameters of the Lorentz group.

Now (hr2)2 = (1)(1) = +1, and the biquaternion curve {exp θ(hr2) : θR} is a unit hyperbola in the plane {x + yr2 : x, yR}. The spacetime transformations in the Lorentz group that lead to FitzGerald contractions and time dilation depend on a hyperbolic angle parameter. In the words of Ronald Shaw, "Bivectors are logarithms of Lorentz transformations." [2]

The commutator product of this Lie algebra is just twice the cross product on R3, for instance, [i,j] = ij ji = 2k, which is twice i × j. As Shaw wrote in 1970:

Now it is well known that the Lie algebra of the homogeneous Lorentz group can be considered to be that of bivectors under commutation. [...] The Lie algebra of bivectors is essentially that of complex 3-vectors, with the Lie product being defined to be the familiar cross product in (complex) 3-dimensional space. [3]

William Rowan Hamilton coined both the terms vector and bivector. The first term was named with quaternions, and the second about a decade later, as in Lectures on Quaternions (1853). [1] :665 The popular text Vector Analysis (1901) used the term. [4] :249

Given a bivector r = r1 + hr2, the ellipse for which r1 and r2 are a pair of conjugate semi-diameters is called the directional ellipse of the bivectorr. [4] :436

In the standard linear representation of biquaternions as 2 × 2 complex matrices acting on the complex plane with basis {1, h},

represents bivector q = vi + wj + xk.

The conjugate transpose of this matrix corresponds to q, so the representation of bivector q is a skew-Hermitian matrix.

Ludwik Silberstein studied a complexified electromagnetic field E + hB, where there are three components, each a complex number, known as the Riemann–Silberstein vector. [5] [6]

"Bivectors [...] help describe elliptically polarized homogeneous and inhomogeneous plane waves – one vector for direction of propagation, one for amplitude." [7]

Related Research Articles

In mathematics, a geometric algebra (GA) is another name for a Clifford algebra of a vector space with a quadratic form over a field of scalars . It is an algebra over generated by the vector space . The multiplication operation is called the geometric product, or the "Clifford product". The elements of the algebra are called multivectors. It contains both the scalars and the vector space . The product determines the quadratic form hence the inner product associated with .

Clifford algebra Algebra based on a vector space with a quadratic form

In mathematics, a Clifford algebra is an algebra generated by a vector space with a quadratic form, and is a unital associative algebra. As K-algebras, they generalize the real numbers, complex numbers, quaternions and several other hypercomplex number systems. The theory of Clifford algebras is intimately connected with the theory of quadratic forms and orthogonal transformations. Clifford algebras have important applications in a variety of fields including geometry, theoretical physics and digital image processing. They are named after the English mathematician William Kingdon Clifford.

Quaternion Noncommutative extension of the real numbers

In mathematics, the quaternion number system extends the complex numbers. Quaternions were first described by Irish mathematician William Rowan Hamilton in 1843 and applied to mechanics in three-dimensional space. Hamilton defined a quaternion as the quotient of two directed lines in a three-dimensional space, or, equivalently, as the quotient of two vectors. Multiplication of quaternions is noncommutative.

Hyperboloid Unbounded quadric surface

In geometry, a hyperboloid of revolution, sometimes called a circular hyperboloid, is the surface generated by rotating a hyperbola around one of its principal axes. A hyperboloid is the surface obtained from a hyperboloid of revolution by deforming it by means of directional scalings, or more generally, of an affine transformation.

Quaternion group

In group theory, the quaternion group Q8 (sometimes just denoted by Q) is a non-abelian group of order eight, isomorphic to the eight-element subset of the quaternions under multiplication. It is given by the group presentation

Cross product Mathematical operation on vectors in 3D space

In mathematics, the cross product or vector product is a binary operation on two vectors in a three-dimensional oriented Euclidean vector space, and is denoted by the symbol . Given two linearly independent vectors a and b, the cross product, a × b, is a vector that is perpendicular to both a and b, and thus normal to the plane containing them. It has many applications in mathematics, physics, engineering, and computer programming. It should not be confused with the dot product.

Unit quaternions, known as versors, provide a convenient mathematical notation for representing spatial orientations and rotations of elements in three dimensional space. Specifically, they encode information about an axis-angle rotation about an arbitrary axis. Rotation and orientation quaternions have applications in computer graphics, computer vision, robotics, navigation, molecular dynamics, flight dynamics, orbital mechanics of satellites, and crystallographic texture analysis.

Rotation (mathematics) Motion of a certain space that preserves at least one point

Rotation in mathematics is a concept originating in geometry. Any rotation is a motion of a certain space that preserves at least one point. It can describe, for example, the motion of a rigid body around a fixed point. Rotation can have sign : a clockwise rotation is a negative magnitude so a counterclockwise turn has a positive magnitude. A rotation is different from other types of motions: translations, which have no fixed points, and (hyperplane) reflections, each of them having an entire (n − 1)-dimensional flat of fixed points in a n-dimensional space.

In mathematics, the Cayley transform, named after Arthur Cayley, is any of a cluster of related things. As originally described by Cayley (1846), the Cayley transform is a mapping between skew-symmetric matrices and special orthogonal matrices. The transform is a homography used in real analysis, complex analysis, and quaternionic analysis. In the theory of Hilbert spaces, the Cayley transform is a mapping between linear operators.

In algebra, a split complex number has two real number components x and y, and is written z = x + yj, where j2 = 1. The conjugate of z is z = xyj. Since j2 = 1, the product of a number z with its conjugate is zz = x2y2, an isotropic quadratic form, N(z) = x2y2.

In abstract algebra, the algebra of hyperbolic quaternions is a nonassociative algebra over the real numbers with elements of the form

In abstract algebra, the biquaternions are the numbers w + xi + yj + zk, where w, x, y, and z are complex numbers, or variants thereof, and the elements of {1, i, j, k} multiply as in the quaternion group and commute with their coefficients. There are three types of biquaternions corresponding to complex numbers and the variations thereof:

In abstract algebra, the split-quaternions or coquaternions form an algebraic structure introduced by James Cockle in 1849 under the latter name. They form an associative algebra of dimension four over the real numbers.

In mathematics, a versor is a quaternion of norm one. The word is derived from Latin versare = "to turn" with the suffix -or forming a noun from the verb. It was introduced by William Rowan Hamilton in the context of his quaternion theory.

In mathematics, a split-biquaternion is a hypercomplex number of the form

In geometry, various formalisms exist to express a rotation in three dimensions as a mathematical transformation. In physics, this concept is applied to classical mechanics where rotational kinematics is the science of quantitative description of a purely rotational motion. The orientation of an object at a given instant is described with the same tools, as it is defined as an imaginary rotation from a reference placement in space, rather than an actually observed rotation from a previous placement in space.

Dual quaternion

In mathematics, the dual quaternions are an 8-dimensional real algebra isomorphic to the tensor product of the quaternions and the dual numbers. Thus, they may be constructed in the same way as the quaternions, except using dual numbers instead of real numbers as coefficients. A dual quaternion can be represented in the form A + εB, where A and B are ordinary quaternions and ε is the dual unit, which satisfies ε2 = 0 and commutes with every element of the algebra. Unlike quaternions, the dual quaternions do not form a division algebra.

Classical group

In mathematics, the classical groups are defined as the special linear groups over the reals R, the complex numbers C and the quaternions H together with special automorphism groups of symmetric or skew-symmetric bilinear forms and Hermitian or skew-Hermitian sesquilinear forms defined on real, complex and quaternionic finite-dimensional vector spaces. Of these, the complex classical Lie groups are four infinite families of Lie groups that together with the exceptional groups exhaust the classification of simple Lie groups. The compact classical groups are compact real forms of the complex classical groups. The finite analogues of the classical groups are the classical groups of Lie type. The term "classical group" was coined by Hermann Weyl, it being the title of his 1939 monograph The Classical Groups.

William Rowan Hamilton invented quaternions, a mathematical entity in 1843. This article describes Hamilton's original treatment of quaternions, using his notation and terms. Hamilton's treatment is more geometric than the modern approach, which emphasizes quaternions' algebraic properties. Mathematically, quaternions discussed differ from the modern definition only by the terminology which is used.

Riemann–Silberstein vector

In mathematical physics, in particular electromagnetism, the Riemann–Silberstein vector or Weber vector named after Bernhard Riemann, Heinrich Martin Weber and Ludwik Silberstein, is a complex vector that combines the electric field E and the magnetic field B.

References

  1. 1 2 Hamilton, W.R. (1853). "On the geometrical interpretation of some results obtained by calculation with biquaternions" (PDF). Proceedings of the Royal Irish Academy . 5: 388–390. Link from David R. Wilkins collection at Trinity College, Dublin
  2. Shaw, Ronald; Bowtell, Graham (1969). "The Bivector Logarithm of a Lorentz Transformation". Quarterly Journal of Mathematics . 20 (1): 497–503. doi:10.1093/qmath/20.1.497.
  3. Shaw, Ronald (1970). "The subgroup structure of the homogeneous Lorentz group". Quarterly Journal of Mathematics. 21 (1): 101–124. doi:10.1093/qmath/21.1.101.
  4. 1 2 Edwin Bidwell Wilson (1901) Vector Analysis
  5. Silberstein, Ludwik (1907). "Elektromagnetische Grundgleichungen in bivectorieller Behandlung" (PDF). Annalen der Physik . 327 (3): 579–586. Bibcode:1907AnP...327..579S. doi:10.1002/andp.19073270313.
  6. Silberstein, Ludwik (1907). "Nachtrag zur Abhandlung über 'Elektromagnetische Grundgleichungen in bivectorieller Behandlung'" (PDF). Annalen der Physik . 329 (14): 783–4. Bibcode:1907AnP...329..783S. doi:10.1002/andp.19073291409.
  7. "Telegraphic reviews §Bivectors and Waves in Mechanics and Optics". American Mathematical Monthly . 102 (6): 571. 1995. doi:10.1080/00029890.1995.12004621.