Hodge conjecture

Millennium Prize Problems
Topological features of a space , such as a hole (labelled by ) are usually detected using singular (co)homology, where the presence of a non-zero class indicates the space has a (dimension ) hole. Such a class is represented by a (co)chain of simplices, depicted by the red polygon built out of 1-simplices (line segments) on the left. This class detects the hole by looping around it. In this case, there is in fact a polynomial equation whose zero set, depicted in green on the right, also detects the hole by looping around it. The Hodge conjecture generalises this statement to higher dimensions.

In mathematics, the Hodge conjecture is a major unsolved problem in algebraic geometry and complex geometry that relates the algebraic topology of a non-singular complex algebraic variety to its subvarieties.

In simple terms, the Hodge conjecture asserts that the basic topological information like the number of holes in certain geometric spaces, complex algebraic varieties, can be understood by studying the possible nice shapes sitting inside those spaces, which look like zero sets of polynomial equations. The latter objects can be studied using algebra and the calculus of analytic functions, and this allows one to indirectly understand the broad shape and structure of often higher-dimensional spaces which can not be otherwise easily visualized.

More specifically, the conjecture states that certain de Rham cohomology classes are algebraic; that is, they are sums of Poincaré duals of the homology classes of subvarieties. It was formulated by the Scottish mathematician William Vallance Douglas Hodge as a result of a work in between 1930 and 1940 to enrich the description of de Rham cohomology to include extra structure that is present in the case of complex algebraic varieties. It received little attention before Hodge presented it in an address during the 1950 International Congress of Mathematicians, held in Cambridge, Massachusetts. The Hodge conjecture is one of the Clay Mathematics Institute's Millennium Prize Problems, with a prize of $1,000,000 US for whoever can prove or disprove the Hodge conjecture.