Subatomic science: 10 things we know (and don’t know) about the fabric of the universe

1. The word “atom” comes from the Greek for “indivisible”, but they’re actually made up of many far smaller particles

Scientists have unpicked atoms and the forces that affect them to discover 61 even smaller particles that make up matter within the universe. (There are likely to be more, but it may be some years before we can find them.) This surprising subatomic world contains weak bosons, strange and charm quarks, tau-neutrinos, photons, muons, gluons and other oddly-named entities.

2. We don’t know what makes up over 95% of the universe

Things that are formed of atoms and molecules like we are – such as stars and planets – only make up around 5% of the universe. The other 95% is thought to consist of dark matter (25%) and dark energy (70%). But no one has yet been able to detect the particles that make up either of these invisible elements – we only know they exist because of how they affect other things.

3. There is not enough gravity to hold our galaxy together

The Milky Way contains 200 billion stars, but when scientists calculate how much they weigh and how fast they’re moving, there doesn’t appear to be enough gravity to explain why they don’t all spin off into space. That’s where dark matter comes in: scientists believe that it acts like cosmic scaffolding, shaping where galaxies form and keeping things in place.

4. Massive clumps of dark matter distort space and time

When we look at very distant galaxies, the light that travels back to us through dark matter is warped by it. So, although we don’t know what dark matter actually is, we can map out where pockets of it exist and what size they are.

5. Dark energy makes up 70% of the universe, but 20 years ago we didn’t even know it existed

In 1929, the astronomer Edwin Hubble produced evidence that the universe was expanding, leading to the Big Bang theory. But it wasn’t until the late 1990s that physicists discovered this expansion was actually accelerating. None of our existing rules explained why this would be happening, which led scientists to identify “dark energy” as the mysterious force that is pulling the universe apart.

6. Around 70 billion neutrinos pass through the tip of your nose every second

Hundreds of billions of miniscule particles go right through our bodies every second without us even noticing. Produced by stars and other astrophysical events, neutrinos have almost no mass at all and travel at almost light speed through the universe – the ones passing through your nose right now were created in the core of the sun only eight minutes ago.

A computer-generation of a supernova

The universe does not behave according to our pre-conceived ideas. It continues to surprise us.

Stephen Hawking (1995)

7. Almost all the antimatter in the universe has disappeared

For every type of particle that exists there is an anti-particle with the opposite electrical charge, and when they meet they cancel each other out.

It’s thought that the Big Bang produced equal quantities of matter and antimatter, which should have completely annihilated each other within moments. Yet instead we ended up with a universe made of matter – and no one can be sure why.

Physicists think there must simply have been slightly more matter in the first place, but it’s even been speculated that entire antimatter galaxies could exist in a mirror region of the universe.

8. We haven’t found the particle for gravity yet, but we have given it a name

Types of particle known as “bosons” control the forces that act on the things around us, but we’ve yet to uncover a boson for gravity. Scientists still don’t know for sure if such a thing exists, but they’ve named the theoretical particle a “graviton”, and used Einstein’s theory of general relativity to outline the properties they would expect it to have.

9. It took 50 years, billions of pounds and trillions of proton collisions to find the elusive Higgs boson particle

The Higgs boson particle was first proposed by Peter Higgs in 1964. It explained how other particles have mass, and became a fundamental part of our understanding of the universe.

In order to prove the Higgs boson’s existence, scientists had to build a vast, multi-billion pound particle accelerator (the Large Hadron Collider at CERN in Switzerland) to shoot beams of protons at each other and study the resulting data. Even then, only one Higgs was observed for every trillion proton collisions. This gives us an idea of just how difficult it could be to identify the mysterious particles that make up dark matter.

10. Physicists like a laugh

Two of the most popular theories for what’s behind dark matter have involved “weakly interacting massive particles” and “massive astrophysical compact halo objects” – or WIMPs and MACHOs, for short.

(Sources: BBC, NASA, New Scientist, PBS, Live Science.)