Large Hadron Collider

Big Bang: Scientists at CERN operate the Large Hadron Collider once more © CERN

Researchers have switched on the Large Hadron Collider after a 27-month break, and they have no idea what their experiments might find. How does it work, and what are they looking for?

  • The Large Hadron Collider. It’s got something to do with physics, yes?

    It has indeed. It is a huge, 27km underground machine between the borders of France and Switzerland, and it is used for experiments by hundreds of scientists at Europe’s nuclear research base, CERN. Essentially, the LHC is a tunnel which beams proton particles at extremely high speeds, and then slams them together to record what happens when they collide. This produces energy densities close to the Big Bang.

    In 2012, the machine led to the discovery of the Higgs boson, and the scientists François Englert and Peter Higgs were awarded a Nobel Prize. They have spent two years updating the machinery, and now their experiments have begun again. The exciting thing is, they have no idea what they might find — our understanding of physics could radically change over the next few months, with some of the biggest breakthroughs since Einstein’s theory of relativity.

  • Hang on - the Higgs what?

    The Higgs boson. Let’s back up and start from the beginning. We know that all of the matter we interact with — the air we breathe, the food we eat, our own bodies — is made from atoms. These are the building blocks of the world around us. The atoms are made from protons, neutrons and electrons, which in turn are made from elementary particles. Scientists believe that all these particles fit into the widely accepted ‘Standard Model’.

  • And the Higgs boson is part of that model?

    Correct. The 12 particles which make up matter come in two different types: quarks and leptons. But these would be useless without the four forces which govern them: gravity, electromagnetism, and two forces which are simply called ‘strong’ and ‘weak’. These forces are not abstract concepts — they exert their power over matter using carrier particles called bosons.

    The Higgs boson is sometimes referred to as ‘the God particle’ as it gives all other particles their mass. This is all quite difficult to wrap your head around, but basically it means that, thanks to the experiments with the LHC, scientists now think they understand most of what makes up the matter in our universe.

  • So what could possibly be left?

    Well, there are still a lot of unanswered questions. For example, despite discovering gravity in the late 1600s, scientists cannot actually account for it in the standard model. Then there’s the fact that all of the matter we have just described — the atoms which make the earth and the stars — only makes up around 5% of the universe.

  • What else is there?

    Scientists think that 27% of the universe is actually something called dark matter, which they know very little about, and 68% is dark energy — which they know even less about.

    Dark matter does not interact with the electromagnetic force, meaning that it does not absorb or reflect light. This makes it extremely difficult to detect. In fact, scientists only believe that it exists because it appears to have some kind of gravitational effect on the matter that we can see. Scientists at CERN are hoping to find out more about dark matter now that the LHC is running again.

  • How are they going to do that?

    The updated machines are able to shoot particles at double the speed of 2012. There are seven experiments happening at various points around the machine, each measuring for different things. But they are truly at the edge of human knowledge — they have no real idea what they might find, or what it will tell us about the universe we live in.

    As CERN’s head of research, Sergio Bertolucci, said: ‘We are going into a vastly uncharted space and there could be big surprises.’

You Decide

  1. Physics is an extremely theoretical science. Do the experiments at CERN change the way you think about the world?


  1. Draw a diagram of an atom and label its various components.


Word Watch

French acronym: Conseil Européen pour la Recherche Nucléaire, or European Council for Nuclear Research.
The Big Bang
We don’t know how the universe began, but scientists widely accept the theory that an unimaginably small, hot and dense space began expanding 14 billion years ago, and the universe was born; they have determined that it is still expanding, and accelerating, all the time.
Einstein’s theory of relativity
This broadened our understanding of motion, space and time.
Discovered by Isaac Newton 300 years ago, the force which pulls matter together: the more matter, the more gravity. This is why large objects such as stars and planets can pull things into their orbit and why objects fall when dropped — pulled towards the centre of the Earth.
The force which attracts or repels electrically charged particles.
Dark energy
Thanks to gravity, the universe should be shrinking — all stars and planets being pulled together. But scientists have observed the universe expanding. How can this be? Physicists believe that dark energy may have the answer.

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Large Hadron Collider
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