Do facts exist? Simon Stevin would have answered ‘yes’ without any hesitation. He did an enormous number and variety of experiments, including the crucial one on that tower in Delft: this is a historical fact. His experiments were quite repeatable, both during his time as well as today, and were often repeated and improved. These are physical facts.

Do laws of nature exist? Not that we know of. Theories evolve, facts remain. Stevin's demonstration of the most remarkable property of falling bodies is as striking today as it was four centuries ago, even though in our time we see it demonstrated in the form of the so-called ‘weightlessness’ of astronauts in their spacecraft. I will follow the historical evolution of the concepts and theories related to Stevin's experiment. Along the way we see theories of motion, collision, accelerated motion, mechanisms that produce acceleration, gravity, space-time curvature, and the bizarre properties of matter in the form of quanta that are described by quantum field theory.

At the point when history becomes present, the path of this research bogs down in a marshy landscape where, at night, will-o’-the-wisps called ‘supergravity’ or ‘string theory’ spread a feeble and misleading light. I fervently hope that this book will inspire someone to find a way ahead. Arthur pulled a sword from a stone, helped by his tutor, Merlin. Maybe a 21st-century girl or boy will perform a comparable feat in physics, helped by a physics professor who teaches her or him that theory is the art of the possible. When we follow the long and winding road from Stevin's beautiful experiment to present observations with giant telescopes and immense particle accelerators, we are confronted squarely with the evolution of scientific understanding: the same observation gives rise to an evolving sequence of explanations and theories. This demonstrates the provisional and temporary character of all results in physics. The phrase ‘law of nature’ is misleading, unless ‘law’ is meant to be similar to laws in society, which are made and amended as needed.

What is commonly called a ‘natural law’ is actually an intermediary link between the makeup of the Universe and our understanding thereof.