Nuclear and particle physics aim to understand the fundamental constituents of matter and the interactions governing them. One powerful approach is to collide protons or atomic nuclei accelerated to near the speed of light, thereby creating new particles and extreme states of matter that can be experimentally observed. In particular, when heavy nuclei such as gold (Au) or lead (Pb) collide at ultrarelativistic energies, a large amount of energy is deposited in a small volume, producing nuclear matter at extremely high temperature and density. Under these conditions, quarks and gluons—normally confined inside hadrons—are expected to exist in a deconfined state known as the quark–gluon plasma (QGP). The QGP provides a unique opportunity to study strong interactions under extreme conditions and offers insights into the state of the Universe microseconds after the Big Bang. In recent years, advances in large-scale data analysis and machine learning techniques have further enhanced the precision and scope of heavy-ion research, highlighting strong connections with modern data science. In this colloquium, I will introduce the basic concepts of heavy-ion collision experiments, discuss the physics of the quark–gluon plasma, and present selected highlights from ongoing research in this rapidly evolving field.