THE HIDDEN UNIVERSE
DARK MATTER AND DARK ENERGY MAKE UP 95 PER CENT OF THE UNIVERSE, YET WE CAN’T SEE THEM. WHAT IS THIS STRANGE STUFF?
Words by Andrew May
DID YOU KNOW? The dark matter in galaxies isn’t just a curiosity – it played an essential role in their formation
As telescopes became increasingly powerful during the 20th century, they started to reveal the true scale of the cosmos. Astronomers discovered that there were billions of other galaxies like our own, scattered throughout a vast, continuously expanding universe. At the same time, advances were made in theoretical cosmology, stemming from Einstein’s theory of general relativity, which showed in precise detail how objects move under the influence of gravity. When those two developments – observational and theoretical – were put together, researchers came to a startling conclusion. By the end of the 20th century, it was clear that all those billions of visible galaxies were just a small fraction of everything there is.
The hidden 95 per cent of the universe goes by the names dark matter and dark energy – but these are two very different things. The word dark is appropriate in the sense that we are ‘in the dark’ about them – we can’t observe them directly, and we don’t know what they are. But it’s misleading to think of them as being dark in colour. That’s true of something like cosmic dust, which we can see quite easily if it gets between us and a bright object that it partially obscures, but dark matter and dark energy are completely transparent. Light across all wavelengths, and all other matter, simply passes through them as if they weren’t there.