51动漫

Progress remains a pipe dream (Image: Peter Ginter/Getty)

IT WAS, in many ways, a declaration of war. A group of physicists has launched a rearguard action to restore experimental data to what they see as its rightful place, back on their subject鈥檚 throne.

Last week, the Perimeter Institute in Waterloo, Canada, hosted its inaugural at the same time as , the world鈥檚 largest string theory conference, was taking place in Bangalore, India. The timing wasn鈥檛 entirely accidental, says Perimeter director . Although string theory attempts to describe the universe in one theoretical framework, it makes no attempt to explain experimental results, he says.

鈥淲e鈥檝e been given these incredible clues from nature and we鈥檙e failing to make sense of them,鈥� he told 51动漫. 鈥淚n fact, we鈥檙e doing the opposite: theory is becoming ever more complex and contrived. We throw in more fields, more dimensions, more symmetry 鈥� we鈥檙e throwing the kitchen sink at the problem and yet failing to explain the most basic facts.鈥�

鈥淲e鈥檙e throwing the kitchen sink at the problem and yet failing to explain the most basic facts鈥�

Turok鈥檚 response: a data buffet. Convergence gave researchers a chance to parade their field鈥檚 most puzzling experimental results, in areas from why 96 per cent of the universe appears to be missing and cosmic inflation to quantum entanglement and the fate of information when matter falls into black holes. The ultimate goal is to give young theorists alternative paths to pursue 鈥� ones guided by empirical evidence.

Several physicists touted dark matter and dark energy as the best areas to focus on. 鈥淒ark matter is the biggest problem in physics today,鈥� said Maria Spiropulu of the California Institute of Technology in Pasadena and CERN鈥檚 CMS collaboration. She suggests that gravity might be the thread that links dark matter 鈥� the invisible stuff that makes up much of the universe鈥檚 mass 鈥� with dark energy 鈥� the even more mysterious stuff forcing the universe apart 鈥� as well as the Higgs boson and the unsolved problem of why neutrinos have mass. That creates fertile ground for new theoretical ideas.

But dark matter has surprised everybody by failing to show up in earthly experiments, not even at the Large Hadron Collider, which was expected to produce it by the bucketload, says Neal Weiner of New York University. Still, there is plenty of scope to devise new ways of looking for it, he said, and theorists shouldn鈥檛 give up. 鈥淲e shouldn鈥檛 confuse the fact that things don鈥檛 happen as fast as we like with the fact that they won鈥檛 happen.鈥�

We may not even need another blockbuster experiment like the LHC to find it. Savas Dimopoulos of Stanford University in California proposed a new kind of institute he calls a 鈥渟uperlab鈥�, to champion small-scale experiments. They are just as likely to give us clues to new fundamental physics as implausible aims like visiting black holes or multibillion-dollar particle accelerators that take decades to build, he said.

The plan is to share resources in an ideas incubator. Researchers in disparate labs are already testing gravity over tiny scales using high-precision instruments called torsion balances, which measure the attraction between two objects. They are also dropping atoms from significant heights to see whether different atoms interact with gravity differently. Bringing such experiments together in a single place could reap large rewards, and even take potshots at string theory by disproving the existence of hypothetical particles it predicts.

鈥淲e can go back to the era where theorists not only came up with theories, but also ways to test those theories,鈥� he said. 鈥淭hese small-scale experiments can keep us excited and keep us making discoveries.鈥�

Quantum cognition

Other physicists presented even more exotic problems for colleagues to chew on. Matthew Fisher of the University of California, Santa Barbara, suggested theorists in search of a challenge could tackle the human brain鈥檚 connection to fundamental quantum physics.

鈥淥ur ultimate challenge is to understand the conduit through which we understand what is 鈥榦ut there鈥�,鈥� he said. 鈥淐ognition is the ultimate mystery.鈥�

John Preskill of Caltech spoke on the quantum structure of black holes and posed a challenge to fellow theorists: 鈥淒oes space-time emerge from quantum entanglement?鈥� he asked. 鈥淭he evidence is building for this.鈥�

Other paths may shed more light (Image: Getty Images)

Not everyone was convinced that the meeting would inspire young theorists to defect from string theory. John Moffat, who works on dark matter at the Perimeter Institute, thinks the academic job market offers little incentive to strike out with radical ideas. 鈥淭his is a straitjacket for them,鈥� he said.

Weiner disagrees. 鈥淚t is hard to take totally new tacks, but I do see young people doing this,鈥� he said. 鈥淚t requires encouragement and training, but it is happening.鈥�

A young physicist may have proved Weiner鈥檚 point during a talk by the Perimeter Institute鈥檚 Kendrick Smith. Smith discussed the implications of the latest measurements by the Planck space telescope for the theory of inflation 鈥� the idea that the universe went through an exponential growth spurt in the first sliver of a second after the big bang. The theory has been on a roller coaster of late, with a team claiming to have found observational evidence and then retracting within a matter of months. Smith thinks more data might not even help, as the theory is adaptable enough to fit any observations we can currently do. He said the theory could easily survive the next 30 years without being falsified.

Paul Steinhardt of Princeton University, one of the original architects of inflation but now a vocal critic of how the theory has evolved, went even further, arguing that inflation鈥檚 flexibility means it cannot even be called a theory.

But Perimeter鈥檚 David Marsh, a 28-year-old postdoctoral researcher, vociferously dissented. He listed observations that would allow the theory to be tested and perhaps disproven, involving the cosmic microwave background鈥檚 鈥渢ensor modes鈥� and the detection of axions 鈥� hypothetical particles originally proposed to solve an unrelated problem.

These kinds of theoretical insights are more necessary than ever, said the Perimeter Institute鈥檚 Natalia Toro. 鈥淲e need to be asking more questions: that鈥檚 what the universe is telling us,鈥� she said. 鈥淓xploratory experiments are becoming ever more important, but they are ever more difficult to do successfully without theoretical input.鈥�

One positive upshot of that is that the future of physics is wide open for theorists and experimenters, Weiner says. 鈥淭en years ago it was obvious what was going to be an interesting thing to work on in two years. Now, I don鈥檛 think I could tell you. It will come from the experimental results between now and then.鈥�

That is why physics must maintain a tenacious grip on experiment. 鈥淭he most important thing is to have experimentalists talking about real phenomena,鈥� Turok says. 鈥淲e鈥檙e at this wonderful stage: we鈥檝e seen the Higgs boson, we鈥檝e seen the whole universe, our reach is further than ever before鈥� and we鈥檙e fundamentally confused. What I think we need now are very simple, radical ideas that will point towards new approaches to the big problems.鈥�

鈥淲e鈥檙e at this wonderful stage: we鈥檝e seen the Higgs boson鈥� and we鈥檙e fundamentally confused鈥�

This article appeared in print under the headline 鈥淏attle for the universe鈥�