The Tenth Anniversary of 'Big Bang Day'

Postcards from the Energy Frontier by Prof Jon Butterworth

Ten years ago it was Wednesday, and at 10:28 in the morning Geneva time the first protons had just made the 27 km journey through the Large Hadron Collider at CERN. The media referred to it as “Big Bang Day”, and while it didn’t mark the start of a new universe, particle physics certainly entered a new era, in more than one way.

The goal of the Large Hadron Collider (LHC) is to bring beams of high-energy particles¹ together in head-on collisions. In the quantum world of sub-atomic particles, concentrated energy is needed to provide resolving power, and you can think of the LHC as being the most powerful microscope ever built, probing the smallest components of the physical universe.

Although no collisions were scheduled for 10 September 2008, and indeed a failure in the magnet interconnects nine days later meant we had to wait a year and a half for the first high-energy collisions, Big Bang Day marked the moment when psychologically speaking we moved from years of planning and construction into operations. The huge detectors had seen some particles, and we knew the experiment was going work in the end.

Another change was in the relationship between particle physics, the public, and the media in between. Big experiments had been done before – in 1989 an electron-positron collider began operations in the same 27 km tunnel, for example. But it seemed like either we hadn’t told anyone, or no one was listening. This time was very different.

The BBC took over a room in the CERN Control Centre. More than a billion people apparently watched Lyn Evans, head of the project, point triumphantly to two spots on a screen and declare success. Crackpot claims that we might somehow destroy Geneva, the world or the universe prompted strange headlines and some serious thinking about the nature of risk. It turned out that a big machine and a potential apocalypse, or a name like “The God Particle”, could get physics onto prime-time news bulletins. Very often a sensible few minutes discussion on what we were actually doing would follow, and (sometimes to the news editor’s surprise) people were interested. 

The whole thing was a new experience for CERN and for particle physicists everywhere. There was a communications strategy behind it of course, and real tangible benefits followed; this article in the CERN courier describes the ups and downs, the triumphs and worries, with depth and clarity. For reasons which are probably obvious, I strongly endorse Roger Highfield’s statement in that article: “the public has a huge appetite for smashing physics“. Long may it continue.

One of the first 3.5 TeV collisions in ATLAS (ATLAS/CERN)

Back to the science though; we broke the record for the highest energy collisions (previously held by the Tevatron in the US) in November 2009, and moved on to run steadily through 2010, 2011 and 2012. The concentrated energies involved are difficult to get a grasp of, but try this. In 2011 the protons had an energy of 3500 Giga-electronvolts (GeV). In the same units, the mass of a proton is a bit less than one GeV. So it is as though we converted the mass of more than 3500 protons into kinetic energy, at an exchange rate of the speed of light squared, and used all that energy to accelerate a single proton. In 2013 and 2014 there was a pause for maintenance and refurbishment. In 2015 we came back with a new record energy (now each proton has an energy of 6500 GeV) and we are still running now, as I write.

We broke into new territory pretty quickly, and the highlight of the past ten years has clearly been the discovery of the Higgs boson. The way the mass of fundamental particles is understood in the “Standard Model” of particle physics requires the existence of quantum energy field present even in the emptiest of space. The Higgs boson is a ripple in that energy field and its discovery was a massive² breakthrough, which won a Nobel prize for two of the theorists involved.

Increasingly precise measurements of the properties and behaviour of this new object have continued (so far) to vindicate the Standard Model. In doing so they constrain the possibilities for dreaming up better theories. Such new theories are needed to explain some of the things the Standard Model leaves out, but as we extend our knowledge off the edge of the theoretical map, more and more of them head for the dustbin. The question “Is the Standard Model isolated?” comes into ever sharper focus.

There is more to the LHC than the Higgs and the search for physics beyond the Standard Model, though. To pick a few highlights, it has discovered new hadrons, revealed new behaviours of light, measured the mass of the W boson, and told us more about cosmic rays and where they might come from. We have learned more about what goes on inside a proton, the quark-gluon plasma, and some surprising possible connections between the two.

The LHC will continue providing collisions until December, and will then shut down for two-years and return in 2021, brighter than ever after a “luminosity upgrade”. This will provide collisions at an even higher rate, and enable us to extend our exploration of the energy frontier still further.

Ten years after the actual Big Bang, the Universe had managed to make protons and helium nuclei and few other bits and pieces, but there was a lot of interesting stuff still to come. The same is true of the Large Hadron Collider.

¹ To be more specific, hadrons, which are particles containing quarks.

² Pun intended.

Professor Jon Butterworth is a physics professor at University College London and a researcher on the ATLAS experiment at CERN involved with, amongst other things, the discovery of the Higgs Boson. He is the author of two popular science books Smashing Physics and A Map of the Invisible. Postcards From the Energy Frontier is the successor to Jon’s hugely successful blog for The Guardian, Life and Physics. He is @jonmbutterworth on Twitter.

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