THE INTERACTIONS BETWEEN CONTROVERSIAL INFRASTRUCTURES, NON-EXPERT CITIZENS AND EXPERTS

In an era increasingly marked by complex socio-technical challenges, from the integration of AI to disputes over sustainable infrastructures, actors such as experts, counter-experts, and non-experts struggle to assert their influence and build or dismantle alliances. In this context, sociology and science and technology studies critically examine traditional frameworks, looking for alternative and situated approaches to investigate these interactions. This dissertation contributes to this conversation by offering new analytical lenses to investigate techno-scientific controversies before they are closed and stabilised. The dissertation focuses on the Nuova Linea Ferroviaria Torino-Lione (NLTL), a cross-border railway infrastructure aiming to connect Turin (Italy) and Lyon (France), investigated as a techno-scientific controversy. Following the cartography of techno-scientific controversies developed by Latour and Venturini, and grounded in the studies proposed by Callon, Pellizzoni, and Collins and Evans, the dissertation maps the evolving interactions among actants. The empirical investigation centres on the Italian online debate surrounding the 2023 report issued by the French Conseil d’Orientation des Infrastructures (COI), which recommended delaying the French section of the NLTL. Guided by three research questions, the study proposes a new understanding of expert figures, revealing how different forms of expertise interacted in this issue. Contributory experts, those with certified technical knowledge, did not significantly shape the online debate on the COI report. Their input was strategically mobilised by interactive experts, such as politicians, who used this knowledge to legitimise existing positions rather than to resolve the controversy. Hence, reflective and interactive experts emerged as key figures, repurposing contributory expertise to either support or oppose the project, with opposing stances lacking the ability to influence the development of the NLTL. Non-experts were largely absent or marginalised in the online debate, pointing to a top-down model of communication. By tracing how expertise is mobilised and contested within the NLTL, this dissertation highlights the evolving dynamics embedded in techno-scientific controversies. It does not aim to provide solutions, but rather to make visible the socio-technical entanglements that define public debates on science and technology, raising critical questions about who gets to speak, whose knowledge counts, and what is left unheard.