"The Hourglass" is an exciting science fiction from the famous American writer Robert Heinlein. This book tells the story of a brilliant scientist who tries to calculate the number of grains of sand on sandy desert beaches while using the latest discoveries and technology. This book fascinates with its deep philosophical undertones, the problems of the limits of our understanding of the universe and the own possibilities of science. It provokes the reader to think about how we perceive reality and what is behind the limitations of our mind. "The Hourglass" is a book that will leave many open questions and offer new ways of thinking.