Physics World June 2015

Three-body problem: solving the proton spin crisis

For nearly three decades, physicists have been unable to answer a seemingly simple question: where does proton spin come from? Adding up the spins of the three quarks that make up the proton seems, in principle, straightforward, but physicists have been struggling with a strange problem: the sum of the spins of its three quarks is much less than the spin of the proton itself. Our cover feature this month examines the origins of the problem – and whether new experiments could mean we are about to solve it at last. Also in this issue, Stephen Ornes explores the strange properties of lattices that are bendy at the edges but not in the bulk, and how they could inspire novel metamaterials that can store data or lead to building materials that only fail in predictable ways.

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