The broader outlines of the physical world, from quarks to the cosmos, have been apparent for decades. Does this mean physicists are about to tie it all up into a neat package? Not at all. Just when you think you know everything, the universe begins to look its strangest.
The detection of what seems for all the world to be a Higgs boson illustrates this idea beautifully. The Large Hadron Collider at CERN near Geneva has provided fodder for physicists from many nations working on a variety of projects but none more important or as eagerly awaited as the confirmation of the Higgs (page 4). Our fly-on-the-wall look at scientists poring over data on small perturbations measured with ultrasensitive instruments shows clearly how answers lead to more questions. The data appear to confirm the Standard Model, the theoretical edifice of particle physics, but also reveal subtle and significant ways in which reality diverges from theory, opening up new vistas for exploration.
Just as physicists thought they had found the smallest building blocks of matter—the tiny quarks and leptons—signs have begun to emerge that there are smaller particles still (page 12). Proof of their existence would throw physics into complete disarray, however. Further, scientists have never fully understood the neutrino—a ghostly particle that rains down on the planet but usually passes through us, and all matter, unnoticed (page 20). The neutrino is therefore another avenue to new inquiries.
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On the largest of scales, scientists feel they are closer than ever before to understanding how the universe began and how it will end (page 36). Yet other mysteries are as deep as they ever were. Dark energy, which helps to explain why the universe continues to expand at an accelerating rate, remains an enduring puzzle. Now some scientists are beginning to suspect that dark energy does not exist after all. If they are right, basic notions of the universe going back to Copernicus would need a radical revision (page 58).
One of the most compelling intellectual problems of our time remains unsolved: How do we tie together the realms of quantum mechanics and general relativity—the very small and the very large? Such a “theory of everything,” which has played cat and mouse with scientists for decades, may remain forever out of reach, argue physicists Stephen Hawking and Leonard Mlodinow (page 90). If that makes you sad, consider that quantum mechanics, an Alice in Wonderland theory that seems to impose severe constraints on what we can know and do, may in fact liberate us by opening a new path to insight (page 102). The universe may be finite, but knowledge has not yet been pegged.