Last September, Catherine Heymans, one of the world’s leading cosmologists, was supposed to board a ferry for the northernmost island in the Orkney archipelago. The island, North Ronaldsay, is among the darkest inhabited places on earth. On a clear winter’s night, it is easy to be awed by the thousands upon thousands of stars visible to the naked eye, which spill their unpolluted light upon the Earth. Heymans, who is the first woman appointed astronomer royal for Scotland, was planning to explain to the island’s 60 or so residents that those stars, and the rest of the perceptible universe, represent a mere fraction of the stuff that makes up our cosmos. What she studies is everything we cannot see: the darkness.
Over the past two decades, Heymans, who is 45, has advanced our understanding of a vast, invisible cosmos that scientists are only beginning to comprehend. That “dark universe” is thought to constitute more than 95% of everything that exists. It is made up of entities more mysterious than the ordinary matter and energy – the light, atoms, molecules, lifeforms, stars, galaxies – that have been the subject of scientific inquiry throughout history. In the past 10 years, Heymans has learned that the dark universe shapes the visible cosmos in unexpected ways, and may not follow all the standard rules of physics. Her discoveries are unsettling a broad consensus on how our world works on its grandest scales. “I believe that, to truly understand the dark universe, we will need to invoke some new physics that will for ever change our cosmic view,” she has written.