Conference : What does ‘time’ even mean?
Marc Lachièze-Rey is a french astrophysicist, cosmologist and theorist at CNRS, working in the laboratory 'AstroParticule and Cosmology' (APC) in Paris. He also teaches at the 'Ecole Centrale' Paris. His scientific publications interests include the topology of space-time, gravity and dark matter. His most important publications include: Au-delà de l'Espace et du temps (2003), Voyager dans le temps : La physique moderne et la temporalité (2013), Einstein à la plage (2015).
In our everyday lives and in some simple problems of physics, we tend to use time. Yet, modern physics (defined by Einstein’s theory of relativity) tells us clearly that time does not exist in nature. For example, clocks measure durations, not time – two closely-related but very different notions. Time is a construction based on durations, and not the inverse. And it can only be constructed through approximations and under certain conditions. Those are the conditions that allow us to use time, yet with limited precision.