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Digital Subscriptions > Prospect Magazine > August 2016 > The science of the inconceivable

The science of the inconceivable

Quantum entanglement embodies a different kind of logic—one that undermines conventional ideas about time and space and makes possible things that are unimaginable

Late last year, an experiment carried out by scientists at the Delft University of Technology in the Netherlands appeared to demonstrate that one object can affect another from afar without any physical interaction between the two. The finding confirmed an idea so extraordinary that, nearly a century ago, Albert Einstein had rejected it with the dismissive phrase “spooky action at a distance.” In quantum theory this phenomenon is known as “entanglement,” and many physicists now regard it as the most profound and important characteristic of the physical world at the smallest scales, which quantum theory describes.

Quantum entanglement is a deeply counterintuitive idea, which seems to contradict human experience of the physical world at the most essential level. In the everyday (“classical”) physical realm, objects affect one another via some kind of contact. The tennis ball flies from the racquet when struck, and when it hits the window the glass will smash. Sure, “invisible forces” seem to act across space—magnetic and electrical attraction and repulsion, say. But in quantum theory these interactions arise from the passage of a particle—a photon of light—between the two interacting bodies. Meanwhile, Einstein showed that the Sun’s gravity corresponds to a distortion of space, to which distant objects such as Earth respond. It’s generally believed that in a quantum theory of gravity (which doesn’t yet exist), this picture will prove to be equivalent to the exchange of “gravity particles” or gravitons between the Sun and Earth.

But quantum entanglement bothered Einstein because it suggested that one particle could affect another even when there was no conceivable physical interaction between them. It didn’t matter if those particles were light years apart—measuring a property of one particle would, according to quantum theory, instantly affect the properties of the other. How could that be?

Entanglement isn’t just another of the strange features of the quantum world, alongside the idea that quantum particles are also waves and that they can be in two places at once, and so on. Rather, entanglement is arguably the central mystery of quantum theory. Pretty much everything that seems odd about the theory is encapsulated in entanglement, an idea that now stands at the very limits of our ability to understand the physical world.

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In Prospect’s August issue: Rachel Sylvester argues that the EU referendum has started a re-alignment of British politics while Roger Scruton and Jay Elwes say that it has thrown Britain into a bout of self-examination with the fundamental question of who we are as a nation at its centre. In addition, Peter Mandelson says without reform the EU could fall victim to a populist uprising. Also in this issue: Philip Ball explores quantum entanglement, George Magnus looks at the political situation in Brazil ahead of the Olympics and Adam Mars-Jones unpicks the work of Steven Spielberg. James Cusick looks at the impact of the Chilcot report and Kathy Lette explains what the world would be like if she was in charge.
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