Étienne Ghys

We are living in a critical time with the steep decline in trust in science. After the Enlightenment era where Reason prevailed over beliefs (especially religious ones), after the industrial revolution and its significant progress for human societies, after the explosion of science throughout the twentieth century, we find ourselves in a dark period where the very idea of truth becomes confused, where the most absurd information circulates everywhere anarchically, without any validation. It would be ridiculous not to question science, which has not only had positive effects, such as the development of nuclear weapons, for example. Climate change is not caused by scientists but is the consequence of a long period of industrialization, without much thought given to the consequences. The scientific community has long neglected its duty to explain to the general public. The challenge is therefore to restore a rational vision in society, without imposing a hegemonic view of science. Science is not everything and should not impose itself everywhere. But one must be modest (which is not the main quality of researchers!). This may be a primary objective, but more precisely, it is a utopia towards which I am trying modestly to move.

I am a mathematician. One characteristic of mathematics is that its history is very ancient. Mathematical results — still difficult today — date back more than 2000 years. There's nothing quite like this in biology, for example. This historical aspect of mathematics has always been important to me. I like the idea of belonging to a community, both in space and time. In fact, I am more motivated and inspired by 19th-century mathematics, particularly by the revolutionary work of Henri Poincaré, in mathematics, physics, and epistemology. His approach, both profound and concrete, is a model for me. It must be said that he did not confine himself to mathematics: by reading him, one understands the links with astronomy, physics, technology, and many other fields. In short, it is the unity of science that fascinates me, even if it is currently threatened by the hyper-specialization of scientists.

A broad question that would deserve lengthy elaboration... If the "thread of time" we are talking about here represents a few decades, it seems to me that the major change is the extreme speed of communication, for example, thanks to the internet. When I was a child, science fiction predicted many wonderful things for the year 2000, but it seems to me that this possibility of communicating instantaneously with the whole world had escaped forecasters. In a way, the scientist was an individual working mainly alone and suddenly became polycephalous. When one thinks of the speed of this evolution, one cannot help but think of the physics of phase transitions or mention Thomas Kuhn's "paradigm shifts." As for the next decades, I prefer to abstain, given the previous observation that the forecasts of a few decades ago were incorrect. Societal transformations? They are clear because the world has transformed into a vast uncontrollable network in which the "Value of Science" (the title of a book by Poincaré!), no longer holds, at least not in its previous form. This value must be rebuilt, adapted to the modern world.

It is impossible to answer this question without specifying the audience for which this book or work is intended. Even with all possible efforts, it must be said that science, and mathematics in particular, are not easy. It takes time, a lot of time, to assimilate even a small part of mathematics. We are no longer in the time of Arago, who taught "Popular Astronomy," or of Poincaré, who wrote books that reached very large audiences. To avoid answering the question directly, I can mention a book that played a role in my vocation when I was a teenager. It is "One, Two, Three... Infinity" by Gamow: the revelation of infinity to a kid! But many other examples could be given. To give a very recent example, David Bessis' book "Mathematica" is remarkable, a bestseller, accessible to a fairly wide audience. Reading this book, I recognized the book of a "mathematical brother"!

A very easy question! I would leave with a digital tablet on which I would have downloaded all the content of the web! I know that such a tablet does not yet exist, but I believe that it should be possible in the not too distant future. Even in my capsule, I would still be in the world! Writing this, I understand that I do not wish to travel alone in a capsule through the universe. I need others.