Physicscalendar_todayLast updated: Apr 2026

What is Quantum Entanglement?

/ˈkwɒntəm ɪnˈtæŋɡlmənt/

A quantum phenomenon where two particles become correlated so that measuring one instantly determines the state of the other, regardless of the distance between them.
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Everyday Example

Imagine two magic coins: whenever you flip one and it lands heads, the other — no matter how far away — instantly lands tails. You can't predict either outcome, but they're always perfectly correlated.

publicReal-World Application

Quantum cryptography uses entanglement to create theoretically unbreakable encryption. Any eavesdropper intercepting a quantum message would disturb the entangled particles, immediately alerting sender and receiver.
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Did you know?

Einstein dismissed entanglement as "spooky action at a distance" in 1935. In 2022, Alain Aspect, John Clauser, and Anton Zeilinger won the Nobel Prize for proving experimentally that Einstein was wrong.

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Key Insight

Entanglement doesn't allow faster-than-light communication — the correlations only reveal themselves when you compare measurements through normal channels. But it remains the strangest phenomenon in all of physics.

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