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Perimeter Institute and the crisis in modern physics

Neil Turok talks to Paul Wells about the ever-increasing complexity of theoretical physics


 

In his welcome speech to this year’s Perimeter Scholars International — captured on video and archived online as is every lecture ever delivered at Perimeter Institute — Neil Turok briefly singled out Jacob Barnett as the youngest member of the class. But the bulk of his message was to the whole class, and indeed, to the international physics community beyond it.

“Theoretical physics is at a crossroads right now,” the eternally boyish South African cosmologist who has run Perimeter since 2008 told the students. “In a sense we’ve entered a very deep crisis.”

The crisis Turok claims to see (not all his colleagues agree it’s there) was provoked by fresh results from two of the most ambitious physics experiments in history. The European Space Agency’s Planck Satellite measures background radiation from near the beginning of the universe’s existence. CERN’s Large Hadron Collider is the highest-energy particle accelerator yet built, designed to look for particles and phenomena on a smaller scale than ever before.

Generations of physicists have built elaborate models, basically sets of equations that fit existing observations and that also predicted what should be found at these two very different scales: the vast and ancient landscape of Planck, and the tiny, fleeting phenomena the LHC examines. “You may have heard of some of these models,” Turok told the class. “There’ve been grand unified models, there’ve been super-symmetric models, super-string models, loop quantum gravity models… Well, nature turns out to be simpler than all of these models.”

When the Large Hadron Collider switched on, lots of theorists predicted it would find other phenomena besides a new particle, the Higgs Boson. Instead it found the Higgs and basically nothing else. “I was at CERN at the time,” Turok said. “Experimentalists were very happy. Theorists were very sad, and they still are. If you ask most theorists working on particle physics, they’re in a state of confusion.”

I got a taste of that during my visit to Perimeter when I visited Philip Schuster and Natalia Toro, two faculty members who were fresh recruits the last time I visited in 2010. These days they’re a little flustered. They had expected the LHC results would shine a little light on something called the Hierarchy Problem, which can be summarized as: Why is there a huge difference between the energy of the Planck scale and the energy of the weak scale? “This is kind of a basic thing, by the way,” Schuster told me, “because if that separation weren’t there, there wouldn’t be a macroscopic universe, period. The universe wouldn’t exist.” So the Hierarchy Problem is a fancy way of asking “Why is there stuff?”, which is an important question to be sure, and after a couple years of LHC there’s no visible answer.

“We were expecting to see a mechanism” to explain the Hierarchy Problem, Schuster told me, “and we haven’t seen a mechanism. And so that’s… interesting. Either it means we’re interpreting things incorrectly; or maybe there is a mechanism and it’s harder to find than we thought; or there’s some even much more radical possibilities… Maybe there is no mechanism and this has to do with the multiverse.” I don’t know what the multiverse is, except that it is suggested by string theory, and this is turning into a long blog post anyway, so let’s just keep moving along. “What is unambiguously uncomfortable and bad about the current situation is that we don’t have a decisive answer,” Schuster said. “That’s just bad.”

“Well, it’s uncomfortable,” Toro said.

“Whatever,” Schuster said. “It’s bad. The point of building this machine was that we would get a decisive answer. And we’re going to have to work harder to get a decisive answer.”

This is the kind of talk Turok gets a real kick out of these days. One of the principle tools of the working theoretical physicist is the “standard model,” which is decades old and describes a lot of the interactions among particles and can predict an awful lot of what happens in the universe. But not everything. Efforts to extend the standard model amount to attempts to understand, well, everything. But insights usually bring clarity, and most of the new physics of the past few decades has brought only ever-increasing complexity.

“The extensions of the standard model, like grand unified theories, they were supposed to simplify it. But in fact they made it more complicated. The number of parameters in the standard model is about 18. The number in grand unified theories is typically 100. In super-symmetric theories, the minimum is 120. And as you may have heard, string theory seems to predict 10 to the power of 1,000 different possible laws of physics. It’s called the multiverse. It’s the ultimate catastrophe: that theoretical physics has led to this crazy situation where the physicists are utterly confused and seem not to have any predictions at all.”

During my visit, I had lunch with Turok in Perimeter’s bustling ground-floor bistro, which opened in 2011.  “The evidence is in. I think, by and large, all the wrong conclusions have been drawn by LHC and Planck,” he said. “The physics world has continued on its merry way, even though I would say the discoveries made really seriously damage conventional viewpoints. I find this really exciting because now it’s time to put up another viewpoint. The hints that are there in the data are, I think, extremely bad for the multiverse picture. They’re bad for super-symmetry, for string theory, and they’re very good for the view that there may be a very simple, powerful theory that will explain all this.”

Golly. If stacks of old theories don’t work, and a new theory is needed, where on earth will somebody come up with some of those new theories?

“The data just fits so perfectly with Perimeter’s mission,” Turok said. “If it had turned out to be complicated and messy — 10 new particles at CERN and all kinds of funny evidence for models of inflation and stuff in the sky — one would have to say the future of theoretical physics does look pretty messy and complicated. Perimeter would be just one of 100 such institutes.

“But given that everything turned out to be very simple, yet extremely puzzling — puzzling in its simplicity — it’s just perfect for what Perimeter’s here to do. We have to get people to try to find the new principles that will explain the simplicity.”

Perimeter Institute has spent part of its 14-year existence establishing its bona fides as a place that can do mainstream physics as well as it gets done at Princeton or Cambridge or Stanford, and part of its time welcoming high-functioning dreamers and visionaries. Lee Smolin, a founding faculty member, wrote a famous book several years ago making fun of string theory’s tendency to get lost in the weeds; his new book argues that time is real, fighting words in some circles in physics. Turok himself grew up as a bit of a trouble-maker. His first book argued that the Big Bang was one in an endless series of expansions, contractions and bangs the universe has gone through. He has lately stepped back from some of his administrative duties at Perimeter to do more thinking and writing, often working with Latham Boyle, a soft-spoken and highly creative young American cosmologist who pops up near the end of my 2010 article on Perimeter.

The spur for Turok’s eager return to the cosmological coalface was the flood of experimental data from Planck and LHC — as well as the CBC’s choice of Turok to deliver the 2012 Massey Lectures, which required that he write a book and deliver a series of lectures from coast to coast on the history of science.

“I was very reluctant to do the Massey lectures because it was so time-consuming,” Turok said. “But it forced me to rethink: What do we do? Where does it fit into the big picture? And that was really fruitful. It made me think, in my own research, I had to focus on the most profound, deep questions, rather than the more routine ones.”


 

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