Tara Shears spent the first 15 minutes of her hourlong Nobel Conference talk outlining our modern understanding of particle physics: 12 types of particles, four forces and an explanation for how they work together.
“The very fact that I’ve spent such a small fraction of my talk on what we understand should tell you that the entire universe is up for grabs when it comes to understanding it,” she said.
It was a happy dilemma, too, for the audience, considering that the mysteries of physics — like antimatter, dark energy and dark matter — capture the public imagination more than the quarks and leptons of the standard model.
Many of those mysteries are being studied at Shears’ workplace, the Large Hadron Collider near Geneva, Switzerland. Shears, also a physics professor at the University of Liverpool, was the second speaker at Gustavus Adolphus College’s 49th annual Nobel Conference. The conference, called “The Universe at Its Limits,” began Tuesday and continues today.
The conference’s title refers both to the tiniest bits of matter and the far reaches of the universe. Shears reinforced that link early.
As it smashes protons together at nearly the speed of light to see what comes out, the Large Hadron Collider is also investigating the primordial universe.
“It tells us what matter is made of at the very tiny scales, but also what the universe was doing in its first seconds of existence,” she said.
The collider is a 16-mile ring about 110 yards under the ground. Inside, a long chain of blue magnets keeps two streams of protons bent in circular paths. There are 40 million collisions a second, each one a re-creation of the conditions of the early universe. The collider has been working since 2010 and has reached about 8 teraelectronvolts, a unit of energy, about half of its design capability.
The nature of antimatter is one of the unanswered questions being studied at the collider, Shears said. The search is hard because if there were lots of it around, you’d know.
If a quarter gram of antimatter meets the same amount of matter, the explosive force equals that of 5,000 tons of TNT. That’s about one-third the power of the atomic bomb dropped on Hiroshima.
The key to antimatter lies in some minuscule difference between it and regular matter, Shears said, something like one part in a billion. If there were equal amounts of antimatter and matter at the big bang, as scientists theorize, then they would have annihilated each other and left no matter.
“But that very tiny difference is the reason why we’re here,” Shears said. “We’re the leftovers.”
It is being investigated in a project called LHCb, which studies the type of quark, called the “b” or “bottom” quark, that is most different in its matter and antimatter forms.
Earlier this year, experimenters made their first measurement of the difference in the number of “b” antimatter and matter quarks produced in a series of proton collisions. It is this difference, again, that researchers are searching for. In the search for this type of antimatter, researchers looked at 70 trillion proton-on-proton collisions and only found the anti-matter particle 1,000 times.
They found about 25 percent more matter than antimatter.
“And that was great,” she said. And it was troubling at the same time because researchers couldn’t explain it with the standard model.
“It means, essentially, we have to patch up this very beautiful, elegant theory with something quite ugly to just try and fit what we see,” Shears said.
And that has happened, but the explanation doesn’t account for nearly enough antimatter.
“We’ve made progress in understanding this question, but there’s more to it,” she said.