Quantum entanglement

Quantun Entanglement was first predicted by Albert Einstein, Boris Podolsky, and Nathan Rosen in 1935.

It has now been (unequivocally) experimentally demonstrated with photons, neutrinos, electrons, and even molecules and crystals :

In 2019, it was announced that 'superposition' had been achieved in an organic compound with more than 2,000 atoms. (ref. Nature, Physics). Then, in 2023, a team from ETH Zurich, announced they had achieved entanglement (for 40 microseconds) at 'macroscopic' scale - in a crystal with approx. 10¹⁶ atoms. (ref.)

Entanglement is defined as :

[…] a physical phenomenon that occurs when a pair or group of particles is generated, interact, or share spatial proximity in a way such that the quantum state of each particle of the pair or group cannot be described independently of the state of the others, including when the particles are separated by a large distance.

Source : Wikipedia

This implies that if any aspect of one of the entangled particles is changed, the other corresponding particles will also be changed. This has now been experimentally verified in multiple experiments.

Since entangled particles can be separated by any distance, a problem arises as to whether the effect is 'instantaneous' - if it is, then it implies 'information' travels faster than lightspeed, which is strictly prohibited by Einstein's relativity theories and the current Standard Model of physics. If the transfer isn't 'instantaneous', however, then current detailed explanations of entanglement must somehow be wrong. This fundamental contradiction has not yet been resolved.

For an extensive technical overview (and the philosophical implications) see Quantum Entanglement and Information, Stanford Encyclopedia of Philosophy.

Also see : Untangling entanglement , Aeon magazine, June 2023.

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