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Favourite Things 6

I haven’t done an entry on my favourite things for a while. If you haven’t read one yet, these posts are about cool (usually geeky) things I think are really amazing and worth talking about. So far I have done the Voyager spacecraft, the iPhone, the Hubble Space Telescope, the McLaren F1, and the SR-71 Blackbird. So what is as cool as these? How about the Large Hadron Collider?

In the unlikely event that you haven’t heard of the LHC or that you want to know a little bit about what it does, I should briefly say what it is. Let’s look at the name: the Large Hadron Collider, and break it down a bit.

First, it’s large. I like the understatement of that word. This thing is huge. Depending on your definition it is the single biggest machine ever built. It is a ring controlled by cooled superconducting magnets 27 kilometers in circumference buried up to 175 metres deep on the border of France and Switzerland near Geneva.

So moving on to “Hadron”. A hadron is a particle made of quarks. The most well-known (if you have done even basic science at school) are the proton and the neutron. The LHC moves protons around its 27 kilometer ring very fast, giving them huge amounts of energy.

Finally there’s “Collider”. After the protons are spun quickly (99.9999991% of the speed of light) around the ring – one beam in one direction and one in the other – they are brought together and collide. The energy is great enough to completely destroy the particles and cause them, and their energy, to transform into a complex shower of exotic particles, including some which might never have been seen before.

So that’s it. It sounds simple doesn’t it? A big ring which spins protons around quickly and crashes them into each other. What’s the point?

Physicists have a model of how the particles in the universe work and there was one element of this model which seemed to be missing. It was a field which gave particles some of their mass (or gave things “weight” if you want to be a bit less technical). There should be a particle associated with this field called the Higgs Boson.

Right, time to explain that. Let’s look at the name again: Higgs Boson. The “Higgs” part refers to Peter Higgs, who is one of the physicists who theorised that the particle should exist in 1964. And “Boson”? A boson is a class of particle and the most important type carry forces. So when a magnet attracts a piece of metal it is because of a stream of bosons called photons.

So a Higgs Boson is just a particle which gives other particles mass (just some of it, not all). Because the Higgs has a high mass it was hard to create in a low energy particle accelerator. Remember that, according to Einstein, mass and energy are related through the famous equation E=mc^2. The LHC is the only accelerator (more or less) with enough energy to make a Higgs.

And the discovery of the Higgs has been tentatively confirmed. In fact that uncertainty is just scientists being cautious because they have found something and, if it isn’t the Higgs, it’s certainly something that is very like one!

Of course the LHC will be used for many other experiments apart from the discovery of the Higgs. Many experiments in particle physics use accelerators to perform collisions and the LHC hasn’t even been run at anywhere near its maximum power yet. There will surely be many more great discoveries made with it.

So now I want to discuss some amazing facts and figures about the LHC. These have been sourced from various web sites but I want o get all the best stuff together in one place here.

1. When the tunnel containing the LHC was dug, after 27 kilometers of digging the two ends met within an accuracy of one centimeter.

2. The cables used at the LHC contain 6000-9000 threads of superconducting niobium–titanium, each one 10 times thinner than a human hair. If you added all the filaments together they would stretch to the Sun and back over six times (about 2 billion kilometers).

3. The particle beams in the LHC only contain 2 nanograms (2 billionths of a gram, or about 10,000 times less than a grain of sand) per day, yet those contain more energy than a 400 tonne train travelling at 150 km/h, and could melt half a tonne of copper.

4. The protons make a complete circuit of the 27 kilometer ring 11,245 times per second. Each beam can circulate for up to 10 hours and travel 10 billion kilometres (equivalent to over 300,000 times around the Earth) in that time.

5. When the experiments are running at the LHC, the four detectors generate 15 million gigabytes of data every year, that is equivalent to one thousand times the information printed in the form of books annually.

6. When the two beams collide they will generate temperatures more than 100,000 times
hotter than the center of the Sun (the highest temperature in the Solar System) but the cooling system that circulates superfluid helium around the LHC keeps it at minus 271.3 degrees Celsius (the lowest temperature in the Solar System).

I often hear people say something like “Why spend tens of billions on the LHC? What practical benefit is there?” I answer that in several ways: first, why must everything have some practical benefit? Some things are just worth doing for themselves. Second, over the time period the cost wasn’t very much, less than what Coca Cola spent on advertising in a similar time. And third, it is impossible to say what unpredicted benefits might come from both the fundamental research from the LHC, and the awesome engineering which went into building it. I’m sure it will repay its cost easily.

Many people think the LHC is one of humanity’s greatest achievements. I agree.

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