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Saturday, July 27, 2013

One Ring To Rule Them All: A Visit To The Large Hadron Collider (Part 1.)

I noticed in telling people about visiting the Large Hadron Collider that a surprising number of folks have never heard of it.  In brief, it's the world's largest and most powerful "atom smasher" --a giant ring 27 kilometers in circumference, buried under hundreds of feet of rock, straddling the Swiss-French border.  It was built to probe the fine structure of matter and space-time, by accelerating tiny bits of matter up to very close to the speed of light and then smashing them together (some people say it's rather like throwing a watch against a wall and watching the bits fly out to see how it works, which is not an exact analogy but it gives you the basic idea.)

 If you know that all the matter you see around you is made of atoms, which are in turn made of smaller particles --protons, neutrons, and electrons --and that these particles interact with each other and with fields like the electromagnetic field, you know enough to go on with.

"You don't have anything on your calendar for the first day you're in Geneva," the PR rmanager's email said. "Anything you'd like to do?" "Well," I wrote back, "I've always wanted to visit the Large Hadron Collider."  I meant it as a joke but apparently, she took me seriously.  The visit to the LHC and CERN took place not on my first day there, which was just as well --I had for some reason (and I don't know why, JFK--GVA is a flight I've made more times than I can count, in the line of duty) absolutely crippling jet lag and my first day I couldn't do much more than lie on the bed in my room at La Reserve, feeling bone-crushingly tired and wishing I could sleep, which I couldn't.  It was no fault of the hotel's --La Reserve is located in the Swiss countryside on the shore of Lac Leman, just outside Geneva; it's one of the most relaxing hotels in Europe but I couldn't nod off for the life of me.  Two glasses of wine with dinner didn't do anything but wake me up, and though I'd brought some melatonin with me I decided --rather foolishly --to white-knuckle it through the night.  Melatonin works as far as sedation goes but it also has been increasingly giving me very, very unpleasant dreams and I've been trying to avoid it, though in retrospect I probably should have just knocked myself out.

The next day started early --my hosts on this trip to Geneva were from a small-batch watch company called Roger Dubuis, which makes a few thousand watches per year for the luxury market in a state-of-the-art facility in Meyrin, which is a suburb of Geneva.  Geneva is both a city and a Canton; Meyrin is located in the Canton of Geneva, which makes the watches made by the company eligible for the prestigious Geneva Hallmark.  This is a quality standard granted by the Canton for watches made to a certain level of quality specified by the Geneva Seal criteria.  It's expensive to adhere to the requirements --the cost over making a standard movement is around thirty to forty per cent --but it's one of the company's main selling points; they remain the only company whose production is one hundred per cent Geneva Seal approved.  

I'd long since forgotten that I'd mentioned the LHC to the company's PR manager in New York as I didn't honestly think that touring the LHC was possible, and I hadn't noticed that on my schedule for the day there were 2 hours set aside for "transport to a surprise destination," which I assumed was an off-site facility of some sort --an engraver, an enamelist's studio, a dial factory.  As it turned out, the surprise destination was indeed the Large Hadron Collider.

The LHC is located at the headquarters of the Conseil Européen pour la Recherche Nucléaire,or CERN, which was established in 1957 with 12 member states and now has 20. CERN's purpose was and is to conduct high energy particle physics experiments, and the Large Hadron Collider is the latest and most powerful particle accelerator --an atom smasher, in popular parlance --in CERN's arsenal.  Basically, particle accelerators like the LHC accelerate subatomic particles up to very high speeds --the LHC takes packets of protons up to very close to the speed of light --and smashes them together in order to explore how matter and the structure of space-time as we observe them today, came into existence.

If you observe the Universe today, you can see that it's expanding (this was an unpleasant surprise for Einstein, who favored a static model) and if you run the clock backwards, the Universe gets progressively smaller and denser and hotter.  At time=zero, theory predicts that the very early universe experienced a phenomenon known as the Big Bang, which began as a moment in time when all the matter and energy in the Universe was concentrated in an extremely tiny area --a dimensionless point of infinite energy and density, or singularity.  

The earliest period of the history of the Universe is known as the Planck epoch, after the physicist Max Planck, and lasted for a very short period of time, known as the Planck Time --this is the amount of time it takes for light to travel the Planck Length, which is an extremely short distance; about 1.616 x 10 to the minus 35th power meters. It's impossible to have an intuitive sense for how tiny such a distance is (the Scale of the Universe animation is pretty good though) but it helps to note that it is about 10 to the minus 20th power smaller than the diameter of a proton.  Evidence for the Big Bang is robust --the left-over radiation from the Big Bang has been detected and mapped by deep space microwave radiation telescopes on satellites like the WMAP probe --and though the Big Bang theory is widely accepted, it raises, to put it mildly, a lot of questions.

Most people would like to know where all the matter and energy (we should just say mass-energy, as by Einstein's equation, E=MC^2, we know they are equivalent) came from, which is a highly speculative subject in cosmology.  Part of the problem is that we do not, at present, have the theoretical tools necessary to make mathematically reliable predictions about the earliest stage of the Big Bang, much less answer questions about where all the stuff that became all the stuff we see now came from.  We can reliably date the age of the Universe to a little over thirteen billion years, but the problem with understanding the very early universe is that during the Planck Epoch, the energy density of the universe was so high that the fundamental forces --the electromagnetic force, weak force, strong force, and gravity --are thought to have been unified into a single force.  

Gravity is the odd man out; we have an excellent theory for gravitation --general relativity --and an excellent theory for subatomic particle behavior --quantum mechanics.  However, when you try to make relativity and quantum mechanics play nice together, terrible things happen --the equations begin to generate ridiculous infinities, which scientists take as evidence that neither relativity nor quantum mechanics are complete theories.  What we want is sometimes given the rather Promethean name of a Theory of Everything --a TOE --which would allow us to make sensible predictions about how gravity works at the quantum scale, but so far a good theory of quantum gravity has proven very elusive.  String theory, which postulates that fundamental particles are not point objects, but instead minute strings of mass-energy whose frequency modes correspond to different fundamental particles, is an attempt to cope with the disconnect between relativity and quantum mechanics; quantum loop-gravity theory is another.

The Large Hadron Collider was constructed to help answer questions about conditions in the early universe.  In particular, one of the major unanswered questions it was designed to look into is the mechanism by which particles acquire mass.  The Standard Model of particle physics, which describes the fundamental particles and their interactions (via quantum mechanics) has successfully described all known subatomic particles, as well as the forces through which they interact, and although it is not complete, it's proven pretty solid ever since it got its name in the 1970s.  The Standard Model also predicted the existence of particles which, at the time it was first being formulated, had not yet been observed.  

One reason certain particles --like the so-called "top quark" --had not yet been observed in existing particle accelerators was that such particles are very massive, and thanks to E=MC^2 we know it takes a lot of energy --a very high energy density --to create such particles in the lab.  Such particles also tend to rapidly decay, as they shed energy, into other, more stable particles.  The top quark was finally detected, after a long search, with a machine called the Tevatron --an enormous particle accelerator located at the Fermi National Accelerator Laboratory (Fermilab) in Illinois, USA.  The Tevatron was a colossus --the main accelerator ring was 6.86 kilometers in circumference, and it collided protons and antiprotons together at TeV --trillion electron volt --energies.  Decommissioned in 2011, it was during its operating lifetime the only machine powerful enough to create and observe the top quark.

Despite its success, the Standard Model has some gaps, one of which is a mechanism for describing why particles that have mass, have mass (why a particle should need to "have" something as basic as mass is another question, but suffice to say there are reasons, which is why things like protons and neutrons have mass, and things like photons don't.)  The Higgs boson is the particle --first hypothesized in 1964 --thought to be responsible for giving mass to certain fundamental particles.  

Bosons are one of two classes of elementary particles (the other is the group known as fermions) and for certain reasons they are often force-carrying particles  in the Standard Model --for instance, photons are the force-carriers for the electromagnetic force.  When particles interact electromagnetically, they exchange photons.  The bosons that mediate such interactions are called gauge bosons, and the Standard Model predicted a field --known as the Higgs field --with which elementary particles would interact in order to gain mass (a massless particle like the photon, by contrast, would not interact with the Higgs field.)  The Higgs boson is the gauge particle of the Higgs field, just as the photon is the gauge particle of the electromagnetic field.  The Higgs field, if it exists, would have a non-zero minimum energy in empty space.

Finding the Higgs boson became, after the discover of the top quark, one of the most important remaining goals in confirming the predictive ability of the Standard Model.

The problem, though, is energy.  Nobody really knew exactly how much energy would be necessary to observe the Higgs boson, and theory predicted that the Higgs field emerged about 10 to the minus tenth power seconds after the big bang --many orders of magnitude after the Planck Epoch (whose duration is the Planck Time, remember --about 10 to the minus 44th power seconds) but still so close to time=zero that the energy density of the universe was extremely high.  It was thought possible that Higgs bosons might have been created in very small numbers in accelerators like the Tevatron, but to make them in large enough numbers to be observed with a high enough confidence to confirm the Higgs field's existence --bear in mind that Higgs bosons exist for too short a time to be observed; what scientists would look for are decay products specific to the decay of the Higgs boson --a bigger machine was needed.  And that's where the Large Hadron Collider came in.

Go to part 2

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