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The symmetry is hidden but is still there
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The symmetry is hidden but is still there
Our universe was probably born symmetrical. At the time of the Big Bang, all particles were massless and all forces were united in a single primordial force. This original order does not exist anymore – its symmetry has been hidden from us. Something happened just 10-11 seconds after the Big Bang. The Higgs field lost its original equilibrium. How did that happen?
It all began symmetrically. This state can be described as the position of a ball in the middle of a round bowl, in its lowest energy state. With a push the ball starts rolling, but after a while it returns down to the lowest point.
However, if a hump arises at the centre of the bowl, which now looks more like a Mexican hat, the position at the middle will still be symmetrical but has also become unstable. The ball rolls downhill in any direction. The hat is still symmetrical, but once the ball has rolled down, its position away from the centre hides the symmetry. In a similar manner the Higgs field broke its symmetry and found a stable energy level in vacuum away from the symmetrical zero position.
This spontaneous symmetry breaking is also referred to as the Higgs field’s phase transition; it is like when water freezes to ice. In order for the phase transition to occur, four particles were required but only one, the Higgs particle, survived. The other three were consumed by the weak force mediators, two electrically charged W particles and one Z particle, which thereby got their mass. In that way the symmetry of the electroweak force in the Standard Model was saved — the symmetry between the three heavy particles of the weak force and the massless photon of the electromagnetic force remains, only hidden from view.
Extreme machines for extreme physics
The Nobel Laureates probably did not imagine that they would get to see the theory confirmed in their lifetime. It took an enormous effort by physicists from all over the world. For a long time two laboratories, Fermilab outside Chicago, USA, and CERN on the Franco-Swiss border, competed in trying to discover the Higgs particle. But when Fermilab’s Tevatron accelerator was closed down a couple of years ago, CERN became the only place in the world where the hunt for the Higgs particle would continue.
CERN was established in 1954, in an attempt to reconstruct European research, as well as relations between European countries, after the Second World War. Its membership currently comprises twenty states, and about a hundred nations from all over the world collaborate on the projects.
CERN’s grandest achievement, the particle collider LHC (Large Hadron Collider) is probably the largest and the most complex machine ever constructed by humans. Two research groups of some 3, 000 scientists chase particles with huge detectors — ATLAS and CMS. The detectors are located 100 metres below ground and can observe 40 million particle collisions per second. This is how often the particles can collide when injected in opposite directions into the circular LHC tunnel, 27 kilometres long.
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Protons are injected into the LHC every ten hours, one ray in each direction. A hundred thousand billion protons are lumped together and compressed into an ultra-thin ray — not entirely an easy endeavour since protons with their positive electrical charge rather aim to repel one another. They move at 99. 99999 per cent of the speed of light and collide with an energy of approximately 4 TeV each and 8 TeV combined (one teraelectronvolt = a thousand billion electronvolts). One TeV may not be that much energy, it more or less equals that of a flying mosquito, but when the energy is packed into a single proton, and you get 500 trillion such protons rushing around the accelerator, the energy of the ray equals that of a train at full speed. In 2015 the energy will be almost the double in the LHC.
A puzzle inside the puzzle
Particle experiments are sometimes compared to the act of smashing two Swiss watches together in order to examine how they are constructed. But it is actually much more difficult than so, because the particles scientists look for are entirely new 0151 they are created from the energy released in the collision.
According to Einstein’s well-known formula E = mc², mass is a kind of energy. And it is the magic of this equation that makes it possible, even for massless particles, to create something new when they collide; like when two photons collide and create an electron and its antiparticle, the positron, or when a Higgs particle is created in the collision of two gluons, if the energy is high enough.
The protons are like small bags filled with particles — quarks, antiquarks and gluons. The majority of them pass one another without much ado; on average, each time two particle swarms collide only twenty full frontal collisions occur. Less than one collision in a billion might be worth following through. This may not sound much, but each such collision results in a sparkling explosion of about a thousand particles. At 125 GeV, the Higgs particle turned out to be over a hundred times heavier than a proton and this is one of the reasons why it was so difficult to produce.
However, the experiment is far from finished. The scientists at CERN hope to bring further groundbreaking discoveries in the years to come. Even though it is a great achievement to have found the Higgs particle — the missing piece in the Standard Model puzzle — the Standard Model is not the final piece in the cosmic puzzle.
One of the reasons for this is that the Standard Model treats certain particles, neutrinos, as being virtually massless, whereas recent studies show that they actually do have mass. Another reason is that the model only describes visible matter, which only accounts for one fifth of all matter in the universe.
The rest is dark matter of an unknown kind. It is not immediately apparent to us, but can be observed by its gravitational pull that keeps galaxies together and prevents them from being torn apart. In all other respects, dark matter avoids getting involved with visible matter. Mind you, the Higgs particle is special; maybe it could manage to establish contact with the enigmatic darkness. Scientists hope to be able to catch, if only a glimpse, of dark matter, as they continue the chase of unknown particles in the LHC in the coming decades.
(http: //www. nobelprize. org/nobel_prizes/physics/laureates/2013/public.. html)
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