Francesca Choquette
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What is Quantum Entanglement?

— Francesca Choquette

Quantum entanglement is a concept from the fascinating and complicated world of quantum physics, that describes two or more particles becoming so entangled that their properties are interdependent, even when they are separated by vast distances. 

Quantum entanglement originated with Albert Einstein, Boris Podolsky, and Nathan Rosen. They researched the idea that particles interact in a way that establishes a spatial relationship between them, and found that by determining the position or momentum of one particle, the other entangled particle’s position and momentum could be found. Einstein named it the Einstein-Podolsky paradox. But this violated one fundamental law: the Heisenberg Uncertainty Principle, which states that simultaneously knowing a particle’s position and momentum is impossible. Einstein and Schrodinger were also unhappy with the concept of quantum entanglement because they thought it implied that particles can transmit information faster than the speed of light in a vacuum, which Einstein had determined to be the universal limit to how fast any object can travel.

This critique was furthered by John Stewart Bell, a physicist from Northern Ireland, who demonstrated that the principle of locality directly contradicted quantum theory. According to the principle of locality, one atom can influence another only if they are touching, which clashes with the Einstein-Podolsky paradox. 

To settle this debate, John Clauser and Stuart Freedman, both American physicists, created an experiment to understand the true nature of quantum entanglement. The experiment involved the decay of calcium atoms to produce two photons of light. According to quantum mechanics, measuring one photon’s polarization should reveal the other’s polarization, even though they are 10 feet apart. Their experiment did indeed provide support for the claim that when entangled particles are placed at opposite ends of the galaxy, measurements on one particle can influence the behavior of its twin faster than the time light could have traveled between them. This dynamic connection between particles, defying the classical lines of thought, underscores the ongoing evolution and complexity of our understanding of the quantum world.


Biron, L. (2022, October 4). Former Berkeley Lab Scientist John Clauser Among Three Awarded the 2022 Nobel for Physics for Work on Quantum Mechanics. Berkeley Lab News Center.

Emspak, J., & Hickok, K. (2023, May 16). What is quantum entanglement?

Ferrie, C. (2023, February 13). Quantum Entanglement Isn’t All That Spooky After All. Scientific American.

Muller, A. (2022, October 6). What is quantum entanglement? A physicist explains the science of Einstein’s ‘spooky action at a distance.’ The Conversation.