From October 6th through 13th, the Nobel Foundation honored achievements in the fields of medicine, physics, chemistry, literature, peace, and economic sciences by announcing the 2025 Nobel Prizes. Two and a half weeks later, many of us will celebrate Halloween, the spookiest holiday of the year. But in 2022, both the Nobel announcement and Halloween were “spooky” in their own ways.

That year, the committee awarded the Nobel Prize in Physics to Alain Aspect, John F. Clauser, and Anton Zeilinger for studying the counterintuitive phenomenon in quantum mechanics known as entanglement. Entanglement refers to the fact that, under specific conditions, pairs or systems of particles can become linked in such a way that they’re always acting as parts of one system, no matter the distance between them.

If a pair of photons or electrons becomes entangled, you could send them to opposite ends of the Galaxy, and measuring the properties of one will still give you information about the properties of the other. For example, if the pair conserves a quantum mechanical property called spin, when you measure one to have clockwise spin, you instantly know the other has counterclockwise spin.

Albert Einstein famously objected to quantum entanglement, framing the phenomenon as “spooky action at a distance.” Einstein, along with the scientists Boris Podolsky and Nathan Rosen, cited the phenomenon as evidence that quantum mechanics was an incomplete theory for explaining reality. They proposed that entangled particles must either communicate with each other faster than light, which is impossible according to Einstein’s Theory of Special Relativity, or have some kind of hidden, underlying properties that physicists have yet to find that explain their long-range connection.

Over the subsequent decades, quantum physicists like Aspect, Clauser, and Zeilinger have produced experimental evidence that challenges the assumptions underlying the Einstein-Podolsky-Rosen paradox. They’ve shown that both conditions are false. Somehow, in a way totally unlike ordinary objects, entangled particles must exhibit corresponding behaviors without communicating with each other or sharing hidden properties that exist before they are observed. Spooky indeed.

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