PROJECTIVE VARIETY Meaning and
Definition
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A projective variety is a fundamental concept in algebraic geometry that encompasses an important class of algebraic sets. To understand projective varieties, it is necessary to first elucidate the concept of projective space. Projective space is an extension of Euclidean space that assigns additional points called points at infinity. It is characterized by the property that any two distinct lines intersect at exactly one point in this space.
Now, a projective variety is a subset of projective space defined by a set of polynomial equations. Specifically, it is the common zero set of a collection of homogeneous polynomials. These polynomials define a collection of points in projective space, with coordinates modulo scalar multiples.
A projective variety possesses several remarkable properties. Firstly, it is homogeneous, meaning it stays invariant under actions of projective transformations. These transformations are linear transformations that map projective space onto itself and include translations and scalings. Moreover, projective varieties are compact, meaning they are closed and bounded in projective space. This compactness property grants them many desirable properties in algebraic geometry.
Projective varieties lie at the heart of the intersection between algebra and geometry, enabling the study of equations and geometric properties simultaneously. They have profound applications in various mathematical fields, including number theory, geometric modeling, and cryptography. To comprehend the characteristics and behaviors of projective varieties, mathematicians have developed sophisticated theories and techniques, such as intersection theory and the theory of algebraic cycles.
Etymology of PROJECTIVE VARIETY
The word "projective" in the term "projective variety" comes from the mathematical concept of projective space. The term "projective" itself derives from the Latin word "projectus", which means "thrown forth" or "projected". In mathematics, projective space is obtained by adding points at infinity to affine space, allowing for a more complete treatment of geometry, transformations, and equations.
The term "variety", on the other hand, refers to a concept in algebraic geometry. It comes from the Latin word "varietas", which means "difference" or "variety". A variety is a geometric object defined by algebraic equations or polynomial equations in several variables.
Therefore, a "projective variety" combines the concepts of projective space and algebraic varieties, representing a geometric object defined by polynomial equations in projective space.
