Introduction

— Isha Upanishad 3

The above quote was the inspiration for the astrophysicist Carl Sagan’s 1995 book The Demon-Haunted World: Science as a Candle in the Dark. The book is an overview of the scientific method that encourages people to learn critical and skeptical thinking skills.

“Science has established beyond any reasonable doubt…”, “physicists have proven that…”, “it is absolutely true that…”—such phrases are abundant not only in popular science but also in academic literature. But is there such a thing as proof in science? Can we ever establish anything beyond any reasonable doubt?

The history of science shows us that scientific theories change through time. What was accepted 500, 250, or even 10 years ago may or may not still be accepted nowadays. In less than half a millennium, we moved from the theory of a finite geocentric universe to our contemporary cosmology. The theory of evolution by natural selection has been accepted for no more than a century. Our phylogenetic tree of life is constantly changing as we discover new species or new relations between species.

Theories in all fields of inquiry change over time. But if our theories change through time, then is there anything unchangeable in the mosaic? In other words: Can we know anything with absolute certainty? Or, alternatively: Is there absolute knowledge? This is the central question of this chapter.