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We’ve discovered the source of mass

December 13th, 2011 · No Comments

Or so it seems..

The Higgs boson and the LHC: at last, a clue to the universe?

Today, scientists working on the Large Hadron Collider will reveal what they’ve learnt about the ‘God Particle’. It’s another exciting step forward in physics, says Sue Nelson.

Energy release: conceptual computer artwork of a reaction at the atomic level. The Higgs boson and the LHC: at last, a clue to the universe?

Energy release: conceptual computer artwork of a reaction at the atomic level Photo: SCIENCE PHOTO LIBRARY

After 30 years in the shadow of biology, physics is in the news as never before. One of life’s big questions – why there is any “stuff” in the universe at all – may be on the verge of being solved. In addition, a tiny particle has been caught breaking Einstein’s cosmic speed limit, and, as a result, travelling backwards in time is being seriously discussed. To cap it all, according to rampant internet rumours, physicists working on the Large Hadron Collider (LHC) at CERN in Geneva are expected to reveal today whether or not they have evidence of the infamous “God Particle”, or Higgs boson.

The Higgs boson is a subatomic particle, the existence of which was proposed by the British physicist Peter Higgs in the Sixties. It is thought to endow everything in the universe with mass. Although Sir Isaac Newton discovered that mass is the source of gravity, and Albert Einstein’s famous equation E=mc² showed that mass is also a form of energy, what mass is and where it comes from remains mysterious.

The Higgs mechanism proposes that mass arises when particles, such as protons, interact with the Higgs field, a sort of force field that permeates everything. The Higgs boson acts as the go-between, allowing the Higgs field to interact with particles that have mass. If the LHC has found the Higgs boson, this will be a momentous event in physics. However, today’s announcement is not expected to deliver a definitive “no” or “yes” that the Higgs exists, but to report evidence suggesting that it does.

So this may see the beginning of the end of one mystery, but other mysteries remain. Much of the excitement in physics at the moment concerns unknowns. This year’s Nobel Prize, for example, went to three scientists who, in 1998, discovered that the cosmos is expanding at an ever-increasing rate, an expansion driven by a mysterious force called dark energy. Even though this research won the Nobel, no one knows what dark energy actually is.

One suggestion is that dark energy is simply another force, which, for some reason, is growing stronger over time. Another that it is a leftover from whatever came before the Big Bang; the truth is that we don’t have a clue.

Similarly, the apparent discovery of faster-than-light particles raises more questions than it answers. Fictional starships aside, nothing should travel faster than 186,282 miles (299,792 kilometres) per second – a cosmic speed limit determined by Einstein more than a century ago. Then, in September, scientists at CERN announced a potential lawbreaker. Subatomic particles called neutrinos had apparently whisked underground from CERN to the Gran Sasso laboratory in Italy, 454 miles (730km) away, faster than the speed of light. According to Dr James Gillies of CERN, “they seemed to be getting there 60 billionths of a second early … or 20 metres ahead of themselves.”

The news made headlines around the world. “This was an enormous story, but it is about scientific process, not whether Einstein was right or wrong,” says Dr Gillies. “The announcement was intended to encourage people to do independent measurements. That’s the way science works.”

Neutrinos are particles with almost no mass and no electrical charge (neutrino is Italian for “little neutral one”). They were first detected in the Fifties by Clyde Cowan and Frederick Reines at Los Alamos, New Mexico, in an experiment nicknamed Project Poltergeist because it was trying to detect the undetectable. Neutrinos are sometimes called “ghost particles”, as they hardly ever interact with solid matter. There are billions passing through your body right now.

Most of these neutrinos are from the Sun, created by the nuclear reactions that make it burn. Neutrinos are therefore thought to have played an important role in the creation of the universe. They come in three “flavours” or types and can oscillate from one type to another. The CERN experiment examined these oscillations, and measuring neutrino speed was an afterthought.

In fact, back in 2007, researchers in America had seen tantalising hints that neutrinos can travel faster than lightspeed. The Minos experiment (Main Injection Neutrino Oscillation Search) measured the speed of neutrinos between the Fermi National Accelerator Laboratory (Fermilab), near Chicago, and a detector in a disused iron mine in Minnesota.

The researchers found that neutrinos travelled faster than light but the margins for error were too wide. Their method, however, paved the way for the development of Gran Sasso’s Opera (Oscillation Project with Emulsion-tRacking Apparatus detector). “Now we have seven times more data,” explains Professor Jenny Thomas of University College London, one of the Minos scientists. The team will verify CERN’s findings – or not – in the next year. And as to how the neutrinos have managed to circumvent Einstein’s rules, there are as many theories as there are particle physicists.

Still there is more. The LHC may have found a solution to the problem of antimatter symmetry. “Nature seems to like symmetry,” says Dr Gillies. “If Nature has a positively charged particle like a proton, it also has a negatively charged antiproton. The problem is when they meet and wipe each other out.”

In theory, when the universe began there should have been equal – symmetric – amounts of matter and antimatter, which would have promptly wiped each other out in a flash of radiation. This would have meant no stars, no galaxies – and no us. Fortunately, there must have been an imbalance – more matter than antimatter. Scientists are searching for what tipped the balance towards matter.

Recently the LHC team reported unexpected differences between matter and antimatter particles, which could explain the surfeit of matter. Scientists are now evaluating whether new theories of nature are needed to explain what happened, such as supersymmetry (Susy), a model in which every particle has a so-called “superparticle” partner – or if the “Standard Model”, which explains the basic properties of forces and particles, needs to be tweaked.

Supersymmetry may even explain the missing “dark matter” that holds galaxies together. “The Standard Model is wonderful at explaining what we see in our experiments, but that’s only a fraction of what we think the universe is made of,” says Dr Tara Shears from the University of Liverpool, who is also working on a CERN project. “It doesn’t tell us anything about dark matter, which is far more prevalent. For that we need a deeper understanding of nature, and Susy is one of the prime candidates.”

So far no Susy particles have been found, and some scientists are questioning if supersymmetry exists. And until its existence is confirmed definitively, some physicists also remain sceptical about the Higgs boson.

“The non-existence of the Higgs is much more likely to be true than neutrinos travelling faster than light,” says Professor Jim Al-Khalili of the University of Surrey, who famously offered to eat his underpants if the latter proved true. “The longer we go on not finding it, the less likely it is that the Higgs really exists.”

Hopefully, we will know for sure very soon. As for the potential faster-than-light, or superluminal, neutrinos, Prof Al-Khalili’s doubts also stem from the fact that it would invoke the possibility of reverse time travel.

For example, if a signal moves faster than light between event A and event B, some observers would see the events in the reverse order. But if the first event causes the second, there’s a problem. “If event A is me firing a gun with a faster-than-light bullet,” says Prof Al-Khalili, “then someone might see a person slump to the ground before I fired the gun. To them, it would appear that the bullet is travelling backwards in time and ending up in the gun barrel. This violates causality. We don’t believe nature allows effects to happen before their causes.”

Prof Thomas agrees that the implications would be mind-boggling. “If it were true about neutrinos,” she says, “it turns physics on its head.” It’s an exhilarating thought. Today’s news on Higgs may be just the beginning.

• Sue Nelson is a former BBC science correspondent and author of ‘How to Clone the Perfect Blonde’. She presents the ‘Space Boffins’ podcast.

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