Digital modeling changes technical practices and develops scientific knowledge: the many testimonies of researchers and engineers gathered in this volume provide an eloquent illustration of this. While the physical sciences, and mechanics in particular, were among the first to resort to numerical modeling and simulation, we have outlined how this trend has developed in many other disciplines. In summary, let us retain from our presentation the following lines of emphasis, complementing those presented at the end of the first volume.

A global technique: In order to be developed as a technique in its own right by a country, numerical simulation requires high-level skills. These are held by mathematicians, physicists, computer scientists, engineers and researchers. A broad scientific community contributing to:

• – developing physical or mathematical models of a phenomenon or set of phenomena of interest for a given discipline or application;
• – developing and validating computational algorithms to produce the data, used for design, production or marketing purposes;
• – operating the computer resources that carry out the simulation algorithms (software and computing machines, with their associated infrastructures, from personal computers to supercomputers);
• – imagining the most varied applications because of their scientific or economic interest.

Countries that now master the entire technique, including the United States, China, Japan, and some European countries (among which France and Germany), are still in small numbers.

A generalized technique: Numerical modeling helps to renew the practice of many scientific disciplines, particularly those that use complex models – such as those of the Universe, climate, the human body and energy – that involve multiphysical, multispecies or multiscale phenomena. Numerical models are a collection of knowledge shared by a scientific community. They testify to the state-of-the-art at a given moment and are continuously enriched by new elements. The results of simulations are interpreted, among other things, with regard to the assumptions on which the models are built and/or the reliability of the data they use. There is always a human dimension to the interpretation of results whose criticism is based on the limitations of using digital tools, assumptions associated with models or practices commonly constructed by a scientific community. While numerical simulation helps to establish recommendations and make decisions (technical, economic, political or other), it is only one tool among others (such as data, measurements, or experimental observations) that it does not replace. Modeling remains imperfect: to date, it has not been possible to fully and accurately account for complex phenomena and, in the case of real systems, models are most often used in a comparative rather than predictive way.

Collective innovations: Numerical simulation is related to communication and information technologies, whose development, dating back one or two decades, has its roots in the second half of the last century. Some major companies in this field are nowadays commercial and global successes, attributed to outstanding personalities. A media story accompanies their success and sometimes suggests the myth of the brilliant and solitary innovator. This may mean forgetting that scientific discoveries are both individual and collective. Technical inventions are made in different parts of the world in different ways – sometimes simultaneously, in a given context: economic or cultural competition, diplomatic or military supremacy. Major industrial projects all require significant public investment. Risk taking is above all collective and sometimes the most ambitious technical projects, based on engineers’ dreams, simply do not see the light of day [CHE 09]. Even if we obviously need an idea, a strength of character, a confidence in your intellectual capacities, as well as a chance to propose and believe in a large-scale project, we never think and innovate alone [ENG 03, HAR 18], that is to say independently:

• – a political, social or economic context;
• – pre-existing knowledge produced by others;
• – currents of thought (and fashions: they also exist in science!);
• – collectively funded infrastructure (transportation, communication, training, etc.).

Innovation genius takes shape, in a spectacular way, in an ability to think outside the box to approach problems in a different way by introducing a disruption* into a scientific, technological and economic environment, and to integrate the elements of an existing one. Depending on their personality – in a combination of deep motivations, connection to the world, personal history and the influence of an environment – some transform an idea into a flourishing company or industrial group, such as American entrepreneur Steve Jobs (1955–2011) [BOY 15]. Others selflessly offer the fruit of their reflection to the scientific community, such as French mathematician Alexander Grothendieck (1928–2014) [SCH 16]. Many researchers and entrepreneurs with a spirit of innovation are familiar with the sources of discovery. Ambitions, doubts, successes, disappointments, competition, rivalry, emulation and cooperation are their daily lives. The vast majority of them also experience innovation as incremental, far from the characteristics attributed to disruptive innovation! These words are attributed to the French engineer Henri Dupuy de Lôme (1816–1885), a 19th-Century innovator:

“When you have such considerable innovations in mind, you have to wait for the right opportunity to make them succeed; otherwise you break, without profit for anyone, against the astonishment of the people that nothing has prepared to listen to you” [https://fr.wikipedia.org/wiki/Henri_Dupuy_de_Lôme].

They remind us that innovation requires taking risks and supposes benefiting from a combination of favorable events, which are not always present. Failure, always relative, is as much a part of the daily life of researchers and innovators as success. It is one of the realities of research and development that we often prefer to ignore in order to focus on success, considered more attractive and remunerative. These failures do not prevent women and men from inventing, undertaking and innovating, every day, in a way that is more or less visible to others. On the contrary, failure may even be a condition of scientific research [FIR 15].

Collaborative research and versatile researchers: The collaborative mode is becoming a necessity for some research actors, both public and private, as Yazid Madi, researcher at the École Polytechnique Féminine, testifies:

“A researcher sometimes has to develop engineering skills: understanding industrial realities and methodologies helps to guide research in a relevant way – and raises exciting academic questions! In engineering sciences, it is quite possible to carry out high-level scientific research with an industrial partnership.”

As we have mentioned several times in the two volumes of this book, numerical simulation and modeling techniques are partly the result of collaborative developments, often carried out in an international context. Knowledge is essentially porous and it is therefore difficult to draw clear dividing lines between various intellectual areas. Referring to numerical simulation, we also encountered other techniques, such as artificial intelligence, and we questioned some of the uses made possible by applications from the digital world and the techniques they allow to develop.

Numerical simulation also contributes to major scientific or technical engineering projects, meeting the fundamental human need to understand, explore and adapt to the world. Many of them – such as observation of the Earth, the Universe, understanding climate and ocean dynamics, improving or researching energy production processes, analyzing living data and biodiversity – involve interstate scientific cooperation, sometimes going beyond the specific interests of each nation. These give a positive meaning to the progress of knowledge in a context where the challenges of the 21st Century seem unprecedented in the history of humanity. A clear statement of the dangers and threats that characterize them can also be accompanied by a form of optimism about the assets that humanity still has to face them [HAR 18, PIN 18a, PIN 18b]. Some techniques will undoubtedly contribute to meeting these challenges and we have outlined how numerical simulation proposes advances that already contribute to them, contributing to the reliability of technical solutions, a more sober or sustainable use of objects, a better use of our resources or collective decision-making. These technical solutions will, among other things, enable humans to adapt to living conditions that will be profoundly altered by current climate and ecological changes, some attributable tour actions on our environement.

Humanity is nothing without technology and technology alone is nothing [CAR 14, ORT 17]. Most of the human contributions, such as creation, imagination, contemplation, intuition, reflection and introspection, to the world are beyond technology’s grasp [CAN 17, MIS 11, SCH 12]. Everyone can state which of these contributions matter to them and give back the salt of life, while digital technology changes our relationship to the world. Creations and destruction are in some respects two sides of the same coin, which is often difficult to accept together. Favoring the former by limiting the latter requires humans to make conscious collective and individual choices – some of which can use techniques. To this day, they remain the freedom of women and men – starting with the freedom to question their use and purposes and to act accordingly on a daily basis, according to one’s means and values. The mastery of digital techniques and their dissemination involves both their designers and users, current and future. It is one of the challenges of the 21st Century – the example of artificial intelligence being one of the most emblematic today. Many scientists and engineers working in different sectors do not act indiscriminately without constantly questioning the purpose of their research. They also contribute to the development of techniques with a humanistic goal, still oriented toward the idea of progress – the improvement or maintenance of good living conditions for most of humanity. They act without naivety, developing an awareness of the limits of their actions vis-à-vis economic or other powers, which can exploit these techniques for other purposes. When they have the independence, freedom and protection that this implies, the most enlightened of them bring the fruits of their research and reflection to as many people as possible. A status, as public research in France today offers them, allows them to do so. Some nowadays see such statutes as a privilege reserved for a minority and granted at the expense of the majority – or as a brake on industrial innovation. It means forgetting that it is at the same time an opportunity for the whole community: the opportunity to remain in control of one’s own destiny.

Beyond unforeseen situations whose probability and safety researchers and engineers try to assess, the risks associated with the development of a technique more certainly lie in their unequal diffusion and especially in their unlimited use for destruction, domination or manipulation. At the collective level, this would be done by humans, especially those of us who have and will have the economic, political or ethical power to guide decisions, not machines or algorithms, even if these resources would be useful for this purpose. The use of a technology is a matter of choice under constraints beyond the majority of humans in their daily lives – in particular, the economic or political power relations and the subtle injunctions of the social system in which they live. In order not to despair collectively of the technologies that humanity also needs in the 21st Century, I believe that the definition of a common decency, the primacy of political choices, involving living together and human values, over economics and technology, remains one of the decisive safeguards. If it is also one of the most difficult to support, humanity still has this possibility to this day. We are obviously largely incomplete in stating this. The purpose here is to talk about a brick that fits into a larger technical building. It is up to each of us to complement it with other resources and perspectives – historical, political, economic or philosophical.

Between Prometheus and Cassander, these words, well-known to the French humanist and writer François Rabelais (Figure C.1) – which some believe the 21st Century will make obsolete – invite us more than ever to continue to question the meaning of the techniques and, beyond that, the conditions in which they are constructed. To do this, it may be a matter of trying to understand how they are created, how they can be controlled and used by humans, for the future of humans – with machines.

COMMENT ON FIGURE C.1.– A 16th Century French writer, Rabelais was the author of the famous aphorism “science without conscience is but the ruin of the soul”. These words can be found in the letter he had Gargantua write to Pantagruel, two of the main characters in his novels. The father’s words trace for his son a humanist path of life, based, among other things, on knowledge: “I commit you to use your youth to progress well in knowledge and virtue […] That there be no scientific study that you do not keep in your memory and for this you will help yourself from the universal encyclopedia of the authors who dealt with it […] When you realize that you have acquired all human knowledge, return to me, so that I may see you and give you my blessing before dying” [RAB 32].