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Inside the Large Hadron Collider

By Stephen Milton

Stephen is a physicist and the chairman of Hastings Humanists. This report complements David Brittain's report about a recent humanist trip to CERN in Switzerland (CERN stands for the Conseil Européen pour la Recherche Nucléaire - the European Organization for Nuclear Research).

The CERN project is a magnificent human endeavour which is aimed at deepening our understanding of the fundamental nature of the universe in which we live. It is an international collaboration, in which the UK is a 16 per cent contributor and in which we have always been a major intellectual participant, aiming at trying to understand the basic rules and fabric of our existence. At its simplest, the Large Hadron Collider (LHC) is a vast circle of densely-packed 21st century technology, which sits like an immense doughnut 100 metres under the Swiss/French border. The collider process is deceptively straightforward. In principle, you take a bit of pure hydrogen gas, strip the electrons away to leave just protons, and then stream the protons into one of two directions at a speed that feels not just improbable, but inconceivable - at just a whisker short of the speed of light.

So how do you move protons that fast? It so happens that these particles respond to magnetism, which is why the Large Hadron Collider is mostly a set of truly immense, and exquisitely powerful magnets, which are frozen to just above absolute zero (-271°C) to make them superconducting.

200 MW of electricity (equivalent to just about all the power generated by one of the two Dungeness nuclear power plants) is used to run the collider, pump two separate streams of protons fired in opposite directions around the 27 kilometre circle, and then smash them into each other in hundreds of collisions that create cascades of subatomic particles, some of which only momentarily exist before decaying into other particles. The impact takes place in a tiny fraction of a second and millions of photographs are taken of these brief cascades. The curve patterns of the flying debris are then analysed in the search for new building blocks of matter. One of those curves represented the Higgs boson, which is sometimes referred to as 'the God particle', because it is the Higgs field which gives us that sense of solid matter that make our existence possible. It was merely a theory for nearly thirty years until the LHC provided proof of its existence.

Several special chambers are designed to capture the cascades from these collisions. The image shows the Atlas detector, and the man standing in the bottom centre of the photo gives you a sense of the sheer size of the detector. (Unfortunately, we were not allowed to see this during our visit). These chambers contain a carefully-designed mix of gases, so as to make visible the particles being searched for. And in these millions of images, scientists look for any anomalies relative to our current 'Standard Model' predictions, which might indicate corrections that need to be made to our understanding of how everything works.

The scale of the endeavour is awe-inspiring. The theoretical underpinnings of the work are far beyond our 'common sense' view of the world, which is built around our bodily interactions with the world, and which is completely different to the tiny quantum world. We've had to create new vocabulary and maths in order to navigate this world, and this can make it impenetrable to the uninitiated. At CERN, there are over 9,000 people who live, eat, dream and think in this bizarre and wonderful place.

We Brits spend in the region of €1.5bn per year on the facility and some may wonder whether this is a sensible expenditure of our financial and people resources. There are lots of reasons why I think this is in our best interests. Here are just three:

Tim Berners-Lee's initial proposal for the World Wide Web was made at CERN (1989)
  • It's a towering tribute to science and the effectiveness of the scientific method in exploring the unknown. I would argue that it is infinitely more valuable than the cathedrals which humans have built.

  • It's justifiable on the basis of the future potential that uncovering the unknown may bring. Just imagine if we were to discover a new source of renewable energy that is effectively free!

  • Tim Berners-Lee invented the World Wide Web at CERN, just one step on the road to the Internet that has done so much to transform our lives over the last few decades. One of the highlights of the trip was to see Tim's initial proposal for the creation of www (WorldWideWeb) communications.

My favourite part of the trip was the time we spent in the canteen. I decided to sit away from our group and mix with the people who worked there. They were all super nice and helpful and interested in what they were doing. I had two questions for them. I didn't get answers but it was fun asking!

First, I met a little group who are helping to prepare a feasibility study for the next stage of expansion of the hadron collider, incorporating a new ring of about 94 kilometres which would enable a six fold increase in the power of the experiments compared to the current 27 kilometre ring. This is in the tradition of CERN. It started in 1957 with a tiny accelerator and it has gone through several upgrades. The expectation is that it will take at least a couple of decades to complete the next stage of expansion, and the feasibility study is just the first step towards understanding the implications - the ground work required, the geology, and the cost.

Next, I sat down with a couple of data scientists, who tried to explain how they manage the vast trove of data that comes out of the particle collisions that can run 24 hours a day and 7 days a week. Some terabytes of data have to be discarded but they have to avoid losing anything useful.

At the coffee machine (which I could not work out how to use), a very nice man listened to my questions and said that he didn't know the answer but would try to find out for me. I wait with bated breath! Then I played table tennis with a couple of Italians who were part of the team that manage the gas that is put into the Atlas detector. This is where the collisions take place. The vapour trails that are photographed are only visible because of the carefully balanced gases that fill the chamber: argon, carbon dioxide and other trace gases such as freon.

Everyone had a sustained interest in understanding some of the most challenging questions about the universe in which we live

The real pleasure came from travelling with a group of people from a wide variety of backgrounds, each of whom had a genuine and sustained interest in understanding some of the most challenging and interesting questions about the universe in which we live. It does not often happen that these kind of subjects can be talked about without the inevitable glazing of the eyes, shrug of the shoulder and the rapid move on to something less interesting!

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