From the photocopier to the fax to a computer's "copy and paste" function, the ability to replicate information is something we take for granted. At the quantum scale, however, making exact copies should be impossible. Now there's a way to dodge this cloning ban that could also help map the border between the "classical", everyday world and the quantum realm - a goal illustrated by the Schrödinger's cat paradox.
The ban arises because, unlike large objects, two or more quantum particles can be entangled, a weird state in which they remain intimately linked even when physically separated. If entangled objects could also be cloned, it would be possible to use them to send a message across space: changing one object would automatically cause an identical change in the other. And this quantum-telegraph message would travel faster than light, violating Einstein's relativity and posing problems for causality.
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