Bell’s Theorem: The Immediate Connectivity of Everything

From many physicists in the 1920’s, the behavior of quantum particles was so unexplainable and counter-intuitive that it led them into believing that there was some yet-to-be known principle (Einstein called it “hidden variable”).

And of course, in their views, that would have been a principle that is consistent with the hitherto conventionally established and accepted physics. The main argument of Einstein and his supporters was what the famous physicist used to call “spooky action at a distance.” This is a phenomenon that seems impossible as far as theory of relativity is concerned, since the latter is incapable of explaining how particles which are entangled on quantum level and that are being separated by great distances from another, are able to change their respective properties simultaneously (non-locality). At the same time, there were not any alternatives proposed as quantum mechanics was slowly but steadily shifting the overall scientific perception to reality.

A major nail in the coffin of the hidden-variables theory comes some 30 years later from the physicist John Stewart Bell, in what is known as Bell’s Theorem. The Irishman found a way to observe the motions and properties of particles that have been entangled on quantum level and that are being separated by great distances from one another.  He developed a series of inequalities (called Bell inequalities), which represent how measurements of the spin of Particle A and Particle B would distribute if they weren’t entangled. In experiment after experiment, the Bell inequalities are violated, meaning that quantum entanglement does seem to take place. 

 

 

Many other experiments have proven Einstein’s claims to be wrong in the period afterwards, but there were still many of supporters of the hidden-variable theory. Those dismissed the results from Bell’s experimental work as being not indicative enough. Accusations for over-simplification are due to the fact that it is extremely difficult for atoms, electrons or light particles to be sustained together within an entangled state for a longer period of time or at a greater distance between them.

In 2015, a team of European physicists led by Ronald Hanson from the Delft University of Technology (The Netherlands) managed to perform sufficiently indicative experimental examination of Bell’s inequality. They “taught” electrons and photons to “exchange” when in entangled state. Using two laboratories at 1.3 kilometers distance from one another, and around 250 pairs of entangled photons and electrons, the physicists managed to prove the validity of Bell’s inequality and that there are no hidden variables explaining the quirkiness of quantum physics. An additional plus of the discovery is that we can now confidently say that quantum encryption systems are absolutely secure, which will would accelerate their development and practical application.

Sources:

The article is published in the information section of Russian site ria.ru. Can be found at https://ria.ru/science/20150828/1212404925.html

The full article with the description of the experiment is titled “Experimental loophole-free violation of a Bell inequality using entangled electron spins separated by 1.3 km”. Can be found at: https://arxiv.org/abs/1508.05949

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