Over 12 billion years ago, speeding particles of light left an extremely luminous celestial object called a quasar and began a long journey toward a planet that did not yet exist. More than 4 billion years later, more photons left another quasar for a similar trek. As Earth and its solar system formed, life evolved, and humans began to study physics, the particles continued on their way. Ultimately, they landed in the Canary Island of La Palma in a pair of telescopes set up for an experiment testing the very nature of reality.
The experiment was designed to study quantum entanglement, a phenomenon that connects quantum systems in ways that are impossible in our macro-sized, classical world. When two particles, like a pair of electrons, are entangled, it’s impossible to measure one without learning something about the other. Their properties, like momentum and position, are inextricably linked.
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