The Case of the Missing Universe

Most of the matter in the Universe is invisible. This mysterious “dark” matter shaped the formation of galaxies, stars, and planets – and therefore our very existence. But how can we learn about something we cannot see? In this talk I will explain how scientists are uncovering the invisible using gravitational lensing, where gravity itself bends light and reveals hidden matter.

Everything you have ever seen, touched, or felt is made of ordinary matter. Yet this makes up only a small fraction of the matter in the universe. Most of it appears to be something we cannot see: dark matter. You may have heard the term in the news or in science fiction, and it might sound mysterious or even speculative. Yet there are clear clues that have convinced astrophysicists that unseen matter is shaping the universe. In this talk, I will show the clues that led scientists to this conclusion and explain why we believe that most of the matter in the universe remains hidden.

Archaeologists use ancient artefacts to reconstruct human history. Galactic archaeologists do the same, but we use stars as our fossils. Each star carries clues about where it formed, encoded in its chemistry and its motion, preserving a record of the Milky Way’s past. Galaxies grow by “eating” smaller galaxies through mergers. By studying these stellar fossils, we can identify which stars were born elsewhere and later accreted into our own galaxy. I will take you through the Milky Way’s past “meals” and “snacks,” explaining how we know its last major meal was a massive galaxy around 10 billion years ago, and how it has been snacking on smaller galaxies ever since. By uncovering these events, we are piecing together how our galaxy formed and evolved over cosmic time.