  In this article, we explore the notion of infinity by studying Cantor's
contribution to this field. A brief history of set theory is given. As an
example of infinity, we consider Hilbert's famous hotel. A graphical
construction is used to demonstrate the countability of rationals. Cantor's
diagonal procedure is explored, demonstrating that the infinity of real numbers
is greater than that of integers. There is therefore a hierarchy of infinities,
enabling us to elaborate on the continuum hypothesis, which remains an unsolved
problem in mathematics.
