SHEDDING LIGHT ON THE DARK UNIVERSE by Dr Alexandra Amon (e2022), Trinity Senior Postdoctoral Researcher
Our planet is an almost infinitesimal speck in the cosmos. It orbits the Sun, one of billions of ordinary stars, which hurtles through our galaxy at about half a million miles per hour. Beyond this, there are billions of galaxies in our Universe, each boasting their own hoard of stars and planets.
In humans’ insignificant snippet in the grand story of the Universe, we have honed a standard cosmological model. It serves as an undeniable success story: with just six parameters, we can describe the evolution of our Universe over cosmic time, from a soup of primordial particles to the web of galaxies in our night sky today. Remarkably, this model has survived rigorous testing by a plethora of cosmological observations – exploding stars as cosmic candles; the distribution of galaxies; and temperature fluctuations mapped in the first light of the Universe. It may sound like we cosmologists have the Universe sussed, but
the elephant in the room is that the cornerstone to this theory is a Universe dominated by dark matter and dark energy. Indeed, just five percent of our Universe is made up of particles whose physics we understand. Dark matter neither emits nor interacts with light. Despite being invisible, and capable of evading particle physicists’ giant underground detectors, it plays a crucial role in the story of our Universe. More than three quarters of the mass in galaxies, including our Milky Way, is dark matter, rather than stars or planets. It exerts a large gravitational effect that glues the stars of galaxies together – dark matter is the invisible scaffolding of our cosmos. Dark energy is even more mysterious. It drives the accelerated expansion of our Universe. That is, our observations reveal that while stars stay tightly bound in galaxies, as cosmic time marches on the galaxies themselves are moving further away from each other at a rate which is getting faster and faster. Our current understanding holds dark energy responsible, but the prediction of its nature by quantum physics is starkly wrong.
© REIDAR HAHN, FERMILAB/DARK ENERGY SURVEY
Blanco Telescope, Cerro Tololo, Chile, for the Dark Energy Survey, under the Milky Way.
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