You may have heard the statement that dark matter makes up about 27% of all matter in the Universe, yet it has never been directly observed.
Multiple questions will inevitably follow this rather matter-of-fact, yet truly mind-blowing statement about dark matter.
How can so much of the Universe consist of something we can't directly see?
And how do we know it's even there?
Come to think of it, what even is dark matter?
Credit: Ralf Kaehler/SLAC National Accelerator Laboratory, American Museum of Natural History
Halloween, 31 October 2024 is, rather fittingly, dark matter day: a day when scientists around the world are promoting the study of one of the biggest mysteries in the Universe.
Dr Lucien Heurtier is a researcher in theoretical particle physics and cosmology at King’s College London.
He has answered 8 of the most common questions about dark matter: what we know and what we don't.
What is dark matter?
No one knows! Scientists are performing experiments in order to try to figure out what dark matter is. It could be made of one or more kinds of particles that don't emit or reflect light – or perhaps black holes as heavy as asteroids that formed shortly after the Big Bang.
How do we know it's there?
Through telescopes, we can see stars and galaxies behaving as if there’s a lot of extra matter exerting a gravitational pull on them, but we don’t see the extra matter directly because it doesn’t emit light.
What is dark matter's impact on the Universe?
Dark matter has been the main form of matter in the Universe since shortly after the Big Bang. Its gravitational pull not only helped galaxies like ours form in the first place, but also helps keep the stars that make up those galaxies trapped inside them today.
How can scientists investigate this invisible force?
Dark matter isn’t a force like gravity, but a substance like air. It’s likely that dark matter, like air, is made of tiny particles – but particles very different from air molecules! Scientists design and build experiments to detect these particles, or look through telescopes to find them.
Where do scientists look for dark matter?
We search everywhere – oceans, mountains, underground, in space, in the atmosphere, even at the South Pole – and with many different techniques. We use satellites, pendulums, microscopes, colliders and cosmic observatories, since dark matter could leave imprints in many subtle ways.
How much of the Universe is dark matter?
Today, around a quarter. That may not seem like a lot, but that’s around five times as much of the universe as ordinary matter. Right after the Big Bang, things might have been different. Scenarios such as "cosmic stasis" even suggest that different kinds of matter may have co-existed for a while. This idea needs to be experimentally tested.
Is dark energy similar to dark matter?
Dark energy and dark matter are very different! Unlike dark matter, which helps galaxies clump together, dark energy makes the universe inflate at an ever-increasing rate. This is sometimes called cosmic inflation. Like dark matter, we don’t yet know much about dark energy.
Do dark energy and dark matter interact?
They might. In fact, a new idea called 'cosmic stasis' suggests that this actually can happen in the early Universe and may even be unavoidable! Even more interestingly, the stasis idea may even lead to a new paradigm for cosmic inflation which might solve many of the difficulties associated with traditional inflation.
Dark Matter Day 2024 events
Find out more about what's happening during Dark Matter Day 2024 via the following sources:
- Interactions.org
- CERN
- University of Oxford
- King's College London
- Dark Matter Day Facebook
- Dark Matter Day X
Do you have any questions or theories about dark matter? Get in touch via contactus@skyatnightmagazine.
