THE standard model of particle physics is a stunning achievement. It offers a concise description of the basic constituents of the universe, the particles and forces that make reality, that agrees with every experimental test we have thrown at it. By most measures, it is the most successful scientific theory ever devised.
But as we explore in our special feature celebrating its 50th anniversary, the standard model remains unfinished. It leaves open several profound questions, from the true nature of dark matter and dark energy to why there is more matter than antimatter in the universe.
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Physicists are desperately seeking an upgraded version, largely by searching for new particles or forces 鈥� or anything in the particles we know of that doesn鈥檛 fit with the existing theory. So far, they have come up empty-handed.
Some say this leaves particle physics in crisis. But one might equally argue that this is just how this kind of research proceeds, as our brief history of the standard model (see 鈥淎 brief history of the standard model, our theory of almost everything鈥�) reveals. It was constructed piecemeal over several decades, through a staccato back and forth between theory and experiment. So perhaps gaps in progress are to be expected, frustrating though they are.
Moreover, there are still many avenues open for us to discover the exotic new physics that would finally take us beyond the standard model 鈥� as we explore in the second part of our special (see 鈥淪ix ways we could finally find new physics beyond the standard model鈥�). Here, six leading physicists share their thoughts on how we will finally complete our brilliant but flawed picture of reality.
Fresh clues might come from the revamped Large Hadron Collider, for instance, which will put the model under even greater strain. We are also expecting final data from an experiment scrutinising the muon, a heavier cousin of the electron, that has hinted at something new. Theorists, meanwhile, are beginning to confront the idea that they might have to rethink their guiding principles.
Put that way, it sounds less like a crisis than possibly the best time to be studying the most exquisite problem in physics.
