PHYSICS is notorious for throwing up concepts that defy our common-sense views of how the world works. One is quantum entanglement. The idea that two particles can instantly affect one another across cosmological distances makes no sense in our existing models of the universe. It certainly offended Einstein. But all the experimental evidence amassed in the past 80 years suggests that it cannot be dismissed.
One inescapable consequence is that space cannot possibly have the structure that Einstein鈥檚 relativity demands of it. Somehow, points in space can be connected to one another, however 鈥渟eparated鈥� they appear to be. And things have just got worse: a new investigation of quantum theory shows that particles can be entangled across time (see 鈥淭he weirdest link鈥�). What are we to make of this? It certainly cranks up the weirdness. If the future can affect the past, our cherished rules of cause and effect fall apart.
But there is a more satisfying conclusion to draw from the idea of entanglement across time, at least for physicists. While Einstein鈥檚 great insight was to label space and time as different sides of the same coin, quantum theory treats them as having fundamentally different qualities. We have known for decades that quantum theory and relativity do not fit together, and that we need a deeper theory to properly describe the universe. Entanglement鈥檚 refusal to sit comfortably within either of these world views confirms that neither has pinned down the nature of reality 鈥� and that the end of physics is still a long way off.
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