World’s biggest machine surely discovers the elusive Higgs boson, helping explain mass. Further quests await.
You’ve surely seen the big science news announced on 4 July: the Higgs boson, aka the God particle, has been discovered. Hooray! Huzzah!
Yet unless you are a theoretical physicist, you might be asking, “The Higgs what?” – for whoever heard of a boson until this week? But you are only reading this column thanks to bosons: the photons streaming from the text into your eyes. And were it not for the Higgs boson and its related field, you would not be here today, but instead the universe would be a place where particles zip around at around the speed of light.
Or that’s what physicists widely believe, anyway. The Higgs field and boson are key components of the Standard Model of physics, which does an excellent job of explaining and predicting how matter behaves at everyday and miniscule scales. The model includes quantum mechanics, a theory so mind-bogglingly weird that even the great physicist Richard Feynman said: ““I think it is safe to say no one understands quantum mechanics.... Nobody knows how it can be like that.”
Parts of the Standard Model are relatively straightforward. Matter comprises fermions, such as the protons, neutrons and electrons that make up atoms. Only one of these can be in the same place at one time – so you can’t walk through walls. Quarks, the building blocks of protons and neutrons, are also fermions, and are so bizarre that they have attributes such as “flavour” no one can taste, and “colour” that can never be seen. They’re named after a drunken seagull trying to order “three quarks” of beer in the baffling novel Finnegan’s Wake.
Then, there are the bosons, which carry forces. Photons are the most familiar, serving as messengers for electromagnetism. Another kind “glue” quarks together, and two more carry weak forces affecting sub-atomic interactions.
Yet these forces could not explain the masses of the four known bosons and various particles, which in turn lead to matter forming structures like you, me, and galaxies. In the early 1960s, six physicists including Peter Higgs proposed that mass results from a field that acts rather like cosmic gloop, and would be associated with a boson. The quest to discover this boson began. Though crucial to theory, it proved elusive, leading to a popular physics book titled The God Particle.
Rather than detect existing God particles, discovering them would rely on first creating the bosons, then observing the particles that they promptly decay into. And this meant unleashing stupendous amounts of energy in a particle accelerator.
Accelerators date from 1932, when John Cockcroft and Ernest Walton “split the atom” for the first time, in Cambridge, UK. Their accelerator was linear, but in North America Ernest Lawrence was developing circular versions, known as cyclotrons, which used magnetic fields to send protons spiralling faster and faster before hitting their targets. His prototype was just five inches (13cm) across, and was followed by versions with diameters of up to 184 inches (467cm), the latter featuring a 4000-ton magnet.
Such accelerators were far too puny for creating Higgs bosons. That has meant creating the world’s largest machine: the Large Hadron Collider at CERN, the European Organization for Nuclear Research, in Geneva. Its power is so great that some even feared it could create a mini black hole that would swallow the earth.
Built 100m underground, the collider has a 27-km circumference. The world’s largest refrigeration system cools the central part to below the temperature of deep space. Mighty magnets accelerate protons through an ultrahigh vacuum, to speeds reaching 99.99999999 percent of the speed of light.
Entering the collision zones, each proton has energy that’s a little more than a flying mosquito. That may not sound much, but the energy is highly concentrated, and there are over 100 million collisions per second. To maximise collision energy, the collider has two proton beams, each with a total energy equivalent to a high-speed train. These approach head on, tightly focused along a path less than the width of a human hair.
Two five-storey high detectors are involved in the search for the Higgs boson, and though the collider only became operational in spring 2010, both have recorded trillions of collisions. Data analyses have revealed that a few dozen of these produced a brand-new particle in a range where the Higgs boson was predicted. It weighs around 125 times as much as a hydrogen atom.
Even as applause and cheers greeted the leaders of the two CERN teams after they presented the results on Wednesday, they were warning that more work is needed to fully confirm the particle is indeed the Higgs boson. Yet they are confident this is the case; so too is Peter Higgs, now 84 years old, who remarked, “I never expected this to happen in my lifetime.”
Ongoing work now includes checking to see if the boson behaves as expected, or contradicts the Standard Model of physics. There are other quests for the collider, too. Physicists will look for evidence of heavy partners of known particles, which are predicted by a grand theory known as supersymmetry: this could help account for the fact we can see only 4 percent of matter in the Universe. They will also try to answer why matter is more plentiful than antimatter, and look for a “quark-gluon plasma” akin to that believed to have existed moments after the Big Bang; this might be created in temperatures 100,000 times those at the centre of the sun.
While many of us might marvel at such wondrous ambitions and accomplishments – and perhaps feel a tinge of pride at belonging to the most intelligent species we know of in the Universe – it is as well to remember that science is also ringing loud alarm bells about our lifestyles, particularly as we turn the global thermostat ever higher. Science underpins progress, yet also warns of needs to slash greenhouse gas emissions, strive for a manageable population. If we heed the warnings, perhaps the forays deep into the quantum realm will someday help our descendants reach to the stars.
Column written for Sunday Morning Post [Hong Kong], published as "Behold the God Particle" on 8 July 2012.