What is science? Science has given us technology and the modern world, has tripled our life expectancy and taught us so much about the universe. Where does its power come from? What makes it reliable? Is scientific knowledge indeed reliable, given the provisional character of all our scientific theories, and in the light of the anti-scientism that is sadly so prevalent in modern society?

I am theoretical physicist involved in the search of a quantum theory of gravity, and I face these questions continuously in the daily practice of my trade. How seriously do I have to take, for instance, the modifications of the nature of space and time that the research appears to be leading to? What do they really mean?

In the book The First Scientist: Anaximander and his Legacy, I offer some thoughts on these questions. I discuss the view that scientific thinking is not limited to the confidence in observation (Francis Bacon) or rationality (Descartes), or restricted to truths that are verifiable (positivism) or falsifiable (Popper). Nor is science restricted to its predictions, to constructing models for classes of phenomena, or to providing certain ("scientifically demonstrated") knowledge. Real science is more than all this.

Science is a passionate search for newer and more effective ways to conceive the world. There is no way to grant its correctness firmly, but it is precisely the awareness of the provisional character of our entire knowledge that makes science reliable: scientific results are not definitive; they are the best ones found so far. The source of the strength of scientific thinking lies not in the certainties it reaches but, quite the opposite, in a radical awareness of their provisional character and of the vastness of our ignorance. This awareness allows us to keep questioning our own knowledge, and therefore to continue learning. Science is not reliable because its results are certain; it is reliable because they are the best we have found so far. The scientific quest for knowledge is not nourished by certainty; it is nourished by a radical lack of certainty.

Contrary to a common image, scientific thinking is never established: it is constantly subversive, visionary, and evolutionary. The aspect of science that I seek to illuminate in this book is its critical and rebellious ability to re-conceive the world time and again. Its ability to overthrow the order of things and built a new conceptual pictures of the world time and again.

I illustrate these ideas making use of a grand and undeservedly unknown figure in the history of human thinking: Anaximander of Miletus, whom I provocatively introduce as the "First Scientist."

Modern science is a vast activity which has many fathers. Many could be named "the first scientist," and I am sure you have your favorite one. By focusing on Anaximander, I wish to illustrate and emphasize one characteristic of scientific thinking that is even more fundamental, I believe, than Galileo's introduction of modern experimentation, or Newton's dynamical laws, or even Ptolemy and Ipparchus' predictive mathematical astronomy or Aristotle's keen observation of nature. What Anaximander started is the process of questioning common knowledge in depth, subverting the shared vision of the world, and proposing a novel conceptual structure for understanding reality. Observed from the particular perspective of a scientist of today, the ideas of Anaximander acquire a new sense, and the immensity of their legacy becomes evident.

Anaximander lived 26 centuries ago in Miletus, a Greek city on the coast of modern Turkey. He understood a surprising number of facts that we consider obvious today, but which had taken humanity millennia to figure out. Foremost, he is the one that first realized (and who was able to convince the world) that the Earth is not lying on something else (columns, turtles, an ocean, earth down forever), bur rather it floats free in space. The sky is not just above our heads: it is all around us, including under our feet.

Karl Popper, the famous philosopher of science, called this idea "one of the boldest, most revolutionary, and most portentous ideas in the whole history of human thinking."

But Anaximander did more. He is the one that started a detailed investigation of natural phenomena such as meteorological ones (rain, wind, thunders, earthquakes) and tried to explain them in natural terms, instead of viewing them as manifestations of the gods. Today every child learns that the water in raindrops comes from the evaporation of the water of sea and land: it is Anaximander who first figured this out.

The novelty of this approach to knowledge six centuries before Christ was total, and its impact has been immense. Daniel Graham, who has studied Anaximander in detail, writes: "Anaximander's project proved in the hands of his successors a program capable of endless development and, in light of its modern incarnation, productive of the greatest advances in knowledge the world has ever known. In a sense his private project has become the grand quest for knowledge of the world."

What Anaximander started, and what in my opinion is the core of scientific thinking, is the process of questioning common knowledge in depth (everybody knows that the sky is above our head, not under our feet), and proposing novel re-conceptualizations of the world, where old concepts change meaning. To make sense of an Earth floating free in space without falling, Anaximander's revolution forces us to modify the notions of "up" and "down." An ancient Greek text explains that "for those standing on their own two feet down below (at the antipodes), high things are low, while low things are high … and so it is all over the Earth." "Up" and "down" become relative to where we are on Earth. It is a step which is not very different, and probably as hard to digest for people at the time, as Copernicus's claim that the Earth moves, Einstein's relativization of simultaneity or today's claim that the very notion of time must be given up in order to conceive a quantum theory of gravity.

I think that such continuous questioning accepted knowledge and re-imagining of the world is a central aspect of the scientific enterprise, not only in major revolutions, but even in everyday laboratory practice. If so, the beginning of the great adventure which is science can be placed not in Newton's laws of motion, in Galileo's experiments, nor even in the early mathematical constructions of Alexandrian astronomy. It must be sought in what can be called the first great scientific revolution in human history--Anaximander's discovery the Earth floats free in space.

This reading of science leads to two considerations. The first follows from the observation that science started precisely at the same time when democracy was being born. Anaximander was a contemporary of Solon, who wrote the first democratic constitution in Athens. Anaximander's Miletus was part of the Ionian league, whose delegates met in the Panionium sanctuary: perhaps the first parliament in the history of humanity. At the very same time when they get rid of kings and emperors, people started looking the world with new eyes and discovered something very new about it. The idea that common decisions are better found in an open discussion where everybody can listen to others and is ready to change his (and, later, her) mind was born together with the idea that we can increase our knowledge by observing, discussing and by changing our minds about the world. Democracy and science are close sisters.

The core of science is therefore not a quest for certainty. Rather, it is a deep acceptance of our persisting uncertainty, and our vast ignorance. Science is born from the discovery that in front of the innumerable aspects of the world that we do not (yet?) understand, accepting our ignorance and being open to learn step by step is far more productive that making up a story and sticking to it.

If the public perception of science had more clarity on these issues, many of the contemporary debates would be less absurd, I think. For instance, Darwinism is under attack in the US on the ground that it is "only a theory, therefore is uncertain." We are not certain that Darwin's evolution theory is the final world about the development of life on Earth, but we are very certain that it is infinitely better that its creationist alternatives! Similarly, the alarms about climate change are underestimated, on the ground that climate scientists "are not completely sure." Which is like doing nothing when there is a fire in the house, unless one is "completely sure" that the house indeed going to be burnt to hashes. We cannot get and we do not need certainty in life: we need reliability, which philosophically might be much weaker, but practically is far more interesting.

This leads to the second consideration, which concerns the relation between the new mode of thinking opens by Anaximander and the mythical and religious thinking from which this new mode of thinking distanced itself. The conflict between scientific and religious thinking started already in ancient Greece. It has continued, with alternate phases, all along these 26 centuries. It can be partially contained, and temporary compromises have been found, but conflict is ultimately inevitable. On a superficial level, because the border between the divine and scientific spheres is always up for debate.

But there is a deeper reason. Which is not because science pretends to "answer all the questions"--as it its often blamed for. But for the very opposite reason: because, unlike religion, scientific thinking does not pretend to answer all questions. It is aware of our ignorance and accepts it. More than this, it constantly questions accepted knowledge.

Religion is a complex phenomenon that touches different aspects of our life and performs multiple functions. For most (not all) structured religions, the persisting doubt which is intrinsic for scientific thinking and the essential distrust of traditional knowledge, is unbearable. They are grounded on truths that do not admit questioning. Eve was curious of the fruit of the tree of knowledge, but God did not like this.

Anaximander's naturalistic approach to understanding the world has won successes that he himself could hardly have dreamed of. But the theistic thought that Anaximander put aside remains the most diffuse form of thinking on our planet. The question raised by Anaximander remains relevant, even burning, today. It divides our civilization. Is it possible to better understand reality, the world's complexity and our own lives without attributing them to the caprices of several gods, or one God? The idea of formulating an understanding of the world without reference to the gods was a radical one 26 centuries ago. It represents one of the deepest roots of modernity. But it is not an idea that has prevailed. Many, perhaps most, people in our world, still dissent.