Harry Cliff - The mysteries in particle physics and fundamental physics

The most straightforward problem to explain is the mystery of dark matter.

About Harry Cliff

"I am a particle physicist at the University of Cambridge, a populariser of science and a science writer.

I work on an experiment called LHCb, which is a giant particle detector on the Large Hadron Collider at CERN, where we study elementary particles – the basic building blocks of our universe."

The enduring mystery of existence

There are many mysteries in particle physics and fundamental physics in general that we can’t answer at the moment. This is why we do experiments at the Large Hadron Collider and elsewhere.

The most straightforward problem to explain is the mystery of dark matter. We know from astronomy that there is about five times more invisible, or dark matter in the universe than ordinary matter. By ordinary matter, I mean stuff made of atoms and particles in the Standard Model of particle physics. This includes gas, dust, stars, planets and people. But all of that represents only about one-sixth of the total matter in the universe. Eighty-five per cent of the matter in the universe is this mysterious stuff called dark matter, which doesn’t interact with, reflect, emit or absorb light. We can tell it’s there from its gravitational influence on the visible universe, but we have no idea what it’s made from and there are no particles in nature that can explain what dark matter is. One of the big hopes is that either at the LHC or some other direct detection experiments underground, we might get a clue as to what the particle of dark matter is.

Perhaps the most embarrassing outstanding problem is that the Standard Model of particle physics, our best theory of the universe, tells us that the material universe should not exist. This has to do with antimatter, which you can think of as a mirror image of the ordinary matter in our universe. In the Standard Model, every particle has an "anti" version. The electron, which is negatively charged, has an "anti" version called the positron, which is positively charged. Our theories tell us that in the early universe, we should have got equal amounts of matter and antimatter created in the Big Bang. But had that happened, either there would be anti-galaxies and anti-stars out there in the universe – and we see absolutely no evidence for that – or matter and antimatter would have annihilated each other and left us with an empty universe. So, the fact that we exist is a big mystery.

Key Points

• It’s a mystery that we exist at all. According to the Standard Model, matter and antimatter should have annihilated each other in the earliest moments of the universe.
• One of the goals of the Large Hadron Collider is to find new particles that may help explain why the Higgs field is so finely balanced. So far, no new particles have been discovered.
• However, physicists at the LHC have encountered anomalies in their experimental results that may suggest the presence of new particles.