Heavy ion collisions reproduce droplets of the trillions-of-degrees-hot liquid that filled the microseconds-old universe, called quark-gluon plasma (QGP). Over the past twenty years, data obtained via recreating this primordial fluid have shown that it is the most liquid-liquid in the universe, making it the first complex matter to form as well as the source of all protons and neutrons. After a look at what we have learned about the formation and properties of this original liquid from heavy ion collisions, I will focus on the questions that motivate experimental measurements coming soon, in particular those that can be answered via the use of jets as probes. (How) can we use jets to see the inner workings of QGP, namely the quarks and gluons that must become visible in the strongly coupled liquid if it is probed with high resolution? (How) can we see the wakes that jets excite in droplets of primordial liquid? Jets in heavy ion collisions at the LHC encode answers to questions governed by very different dynamics of the primordial liquid arising at different length scales, making it imperative to define/design new observables and strategies for teasing apart the answers.
PHYSICS COLLOQUIUM: https://indico.dfa.unipd.it/event/974/
