The coolest place in the universe
The Large Hadron Collider at Cern is a thing of wonder – not just for smashing 600 million protons together a second, but for uniting 10,000 scientists from 113 countries in the pursuit of knowledge.
The discovery of a Higgs-like particle by the Large Hadron Collider at the Organisation Européenne pour la Recherche Nucléaire (known as Cern) was the greatest scientific story of 2012. It is also a spectacular demonstration of what can be achieved when the intellectual power of theoretical physics is coupled with engineering and international collaboration. In those first two sentences, I’ve already used two hyperbolic adjectives; let me explain why I feel justified in doing so.
The Higgs boson is a fundamental subatomic particle whose existence was predicted in a series of papers in 1964 by a group of theoretical physicists including Robert Brout, François Englert, Peter Higgs and Tom Kibble. The prediction was made partly on aesthetic grounds – by which I mean it was introduced to make the equations that describe how subatomic particles interact with each other more elegant. Technically, the Higgs mechanism is a means of preserving certain symmetry properties of the equations which are considered to be desirable, or even “beautiful”. As such, the successful prediction of the Higgs boson can be regarded as a prime example of what the physicist Eugene Wigner termed “the unreasonable effectiveness of mathematics in natural sciences”.
Its job is to give mass to the other fundamental particles, including the electrons and quarks out of which we are made. It does this by interacting with them, and the strength of the interaction determines the mass of the particle; electrons are less massive than top quarks because they interact more weakly with Higgs particles. The Higgs particles fill all of space. Every cubic meter of the room in front of you is crammed with Higgs particles. They occupy all of the space inside your body, outside your body, and throughout and between every galaxy in the observable universe.
How did the Higgs particles get there? The answer is not yet known but it is thought that they “condensed out” into the universe less than a billionth of a second after the Big Bang as the universe expanded and cooled. This is a process not dissimilar to ice crystals forming on a cold window on a frosty morning. Water vapour in the air undergoes what physicists call a phase transition when it comes into contact with the cool glass. The symmetry of the vapour state is broken and the intricate structural forms of ice crystals spontaneously emerge. This happens because it is energetically favourable; at low enough temperatures, water molecules can release energy by bonding together into clumps, rolling down a metaphorical hill and settling into a valley floor. Similarly, the “empty” vacuum of space has a lower energy when filled with a condensate of Higgs particles, which is ultimately the explanation for why there is any large-scale structure in the universe at all.
This sounds odd and it gets odder. If we naively calculate the energy locked up in the Higgs condensate, it is bordering on the absurd. In every cubic meter of space the condensate stores 1037 joules, which is more energy than the sun outputs in 1,000 years. This should blow the universe apart but it doesn’t, for reasons that nobody understands.
Despite all this, we have discovered that it is broadly correct: space really is crammed full of Higgs particles, and we really are bumping into them all the time. This gives us our mass at the most fundamental level, and without this strange and convoluted mechanism we would not exist. The slight caveat is that there are many differing Higgs-like theories, each leading to Higgs particles with different properties. Some of these theories predict that there is more than one type of Higgs particle. This is why, technically speaking, Cern always refers to the new particle as “Higgs-like”. There is more work to do to pin down precisely which Higgs has been seen, but what is now beyond reasonable doubt is that a new particle, which behaves roughly like the so-called Standard Model Higgs Boson, has been produced and detected.
The discovery of the Higgs is more than a profound vindication of advanced mathematics and its application in theoretical physics. It is also a surprising engineering and political achievement. No single nation is prepared to invest in a project as technically difficult and high-risk as the Large Hadron Collider. The machine itself is 27 kilometres in circumference and is constructed from 9,300 superconducting electromagnets operating at -271.3°C. There is no known place in the universe that cold outside laboratories on earth; in the 13.75 billion years since the Big Bang occurred, the universe is still roughly 1° warmer than the LHC. This makes it by far the largest refrigerator in the world; it contains almost 120 tonnes of liquid helium.
Buried inside the magnets are two beam pipes, which, at ultra-high vacuum, contain circulating beams of protons travelling at 99.9999991 per cent the speed of light, circumnavigating the ring 11,245 times every second. Up to 600 million protons are brought into collision every second, and in each of these tiny explosions, the conditions that were present less than a billionth of a second after the Big Bang are re-created. Four giant detectors, known as ATLAS, CMS, LHCb and ALICE, diligently observe each collision, searching for new physical phenomena such as the Higgs, searching for a needle in a thousand haystacks.
In order to construct and operate this group of complex, interdependent machines, more than 10,000 physicists and engineers from 608 institutes in 113 countries collaborate with each other for the sole purpose of enhancing our knowledge of the universe.
Cern’s founding convention, written in 1954 as part of the reconstruction of Europe after the Second World War, makes this purpose explicit: “the Organisation shall provide for collaboration among European States in nuclear research of a pure scientific and fundamental character . . . the Organisation shall have no concern with work for military requirements and the results of its experimental and theoretical work shall be published or otherwise made generally available”.
Cern, in other words, is a place of high ideals that actually works. Its budget, shared between many nations, is approximately that of a single medium-sized European university. Free from the usual bureaucratic and political interference that dogs large international collaborations, managed almost exclusively by scientists and engineers, it has consistently delivered some of the most complex engineering projects of the past 60 years on time and on budget. In doing so, as a spin-off, it has invented the World Wide Web and many of the technologies used in medical imaging and the newly emerging field of proton beam cancer therapy. This, in the modern jargon, is known as “impact” – a tremendous return on society’s investment. But, very importantly indeed, this impact came as a side effect of the exploration of nature for its own sake.
I find all this to be deeply inspiring; it makes me optimistic for the future of the human race. First, we have been able to discover something profound about our universe. How astonishing it is that, to paraphrase Douglas Adams, a small group of apes on an insignificant rock among hundreds of billions in the Milky Way galaxy were able to predict the existence of a piece of nature that condensed into the vacuum of space less than a billionth of a second after the universe began 13.75 billion years ago. And how wonderful that they did this together; that there is a place where people put their religious, political and cultural differences aside in the name of exploring and understanding the natural world.
That sounds ridiculously idealistic and bordering on the naive, but Cern is a place that confounds and confuses in equal measure because it is idealistic. There is no agenda other than the advancement of our understanding. That is why it works and that is the key to understanding why it exists and what it does.
Over the coming decades, the LHC will continue to produce Higgs particles and the experimental scientists will measure their properties in ever-greater detail to understand better how nature works at the most fundamental level. They will also be on the lookout for unexpected physics, because the LHC is operating at the edge of our understanding. They will, no doubt, make further contributions to the economies of Cern’s member states and the well-being of their citizens but this is not a reason, and never can be, for the exploration of nature.
In 1969, the US physicist Robert R Wilson was called before a Congressional committee to justify the funding of Fermilab, the US equivalent of Cern. Asked to justify the expenditure on the project, in terms of enhancing national security and the economic interests of the United States, Wilson replied: “It has only to do with the respect with which we regard one another, the dignity of men, our love of culture. It has to do with: are we good painters, good sculptors, great poets? I mean all the things we really venerate in our country and are patriotic about. It has nothing to do directly with defending our country except to make it worth defending.”
Cern’s tremendous achievements in 2012 fall into the same category. Because of the Large Hadron Collider, we understand our universe significantly better than we did in 2011, and that is a wonderful thing.
[Editor's note: This piece originally had the headline "The coldest place in the universe". Since we went to press, it was pointed out that the Boomerang Nebula is the coldest known region in the distant universe. As Brian Cox tweets: "That's science".]
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