There is a fundamental mismatch between the computational basis of spreadsheets and our knowledge of the real world. In spreadsheets numerical data is represented as exact numbers and their mutual relations as functions, whose values (output) are computed from given argument values (input). However, in the real world data is often inexact and uncertain in many ways and the relationships, i.e., constraints, between input and output are far more complicated. This paper shows that Interval Constraint Solving, an emerging Artificial Intelligence based technology, provides a more versatile and useful foundation for spreadsheets. The new computational basis is 100% downward compatible with the traditional spreadsheet paradigm. The idea has been successfully integrated with Microsoft Excel as the add-in Interval Solver that seamlessly upgrades the arithmetic core of Excel into interval constraint solving. The product has been downloaded by thousands of end-users in about 70 countries around the world and has been used in various applications on business computing, engineering, education and science. There is an intriguing chance for a major breakthrough of the AI technology on the spreadsheet platform: Tens of millions of Excel users are making important decisions based on spreadsheet calculations.