What were the biggest physics discoveries of 2015?
I asked our Nature of Reality contributors which advances they think will have the biggest impact in the years to come. And while some of their answers will be familiar from this year’s most popular headlines, others may come as a surprise.
The Large Hadron Collider didn’t deliver a Higgs-style blockbuster this year, but the December release of results from the “big bang machine’s” second, more powerful run ranked high on both Paul Halpern and Sabine Hossenfelder’s lists. “Lots of ‘maybes’ from Run 1 have gone away,” says Hossenfelder, assistant professor for high energy physics at Nordita in Stockholm. “This is very important for the field.” In his recent post on the anomalous “bump” in the data from the 2015 run, Fermilab physicist Don Lincoln called the run “a dazzling success,” adding that the data include “approximately sixty new physics results.” Most of those results agreed with previous predictions: not the stuff of flashy headlines, but the kind of thing that helps physicists sleep better at night. (And most everyone, from physicists to journalists, is withholding judgment on the significance of that strange bump.)
To Halpern, a professor of physics at the University of the Sciences in Philadelphia, the new LHC results exemplify “frontier” physics. “In the past year we have explored two longstanding frontiers: the traditional outer limits of the solar system and the high energy regime corresponding to the upper bounds of the Standard Model of particle physics,” says Halpern, referring to the New Horizons mission, which reached Pluto in July, and the latest LHC run. During its closest approach to Pluto’s surface, New Horizons revealed mountains that could be ice volcanoes and showed that vast swaths of Pluto’s surface are geologically very young. It also delivered the first high-resolution images of Pluto, and while pictures alone don’t make science, they have transformed Pluto from an abstraction—a hazy smudge—into a detailed and particular world.
While the Higgs discovery had the satisfying ring of a story’s final chapter, these advances have a middle-of-the-book quality: science is still turning over new pages. “As we probe the features of Pluto and test the properties of the Standard Model, our hope is to press even further and explore domains beyond those limits, namely the Kuiper Belt objects beyond Pluto and possible new particles beyond what the Standard Model predicts,” says Halpern.
Frank Wilczek also picked new particles and Pluto as the year’s most (potentially) groundbreaking results. “If the recent hint of a two photon resonance at the LHC holds up (which is very much in doubt), it could be a very fundamental discovery with wide-ranging impact,” says Wilczek. But with the jury still out on that, as well as other frontier work, Wilczek gives the nod to New Horizons. “It showed in a dramatic fashion that physics really works, and gave humankind some images that will inspire people for decades to come.”
Now, from the edge of the solar system to the boundary between gravity…