Nobel Prize for Bell Test Experiments

It has long been argued that John Stewart Bell deserved a Nobel prize for work he did in the 1960s. A prize has now been given for experiments testing his theorem:

Alain Aspect, John Clauser and Anton Zeilinger have each conducted groundbreaking experiments using entangled quantum states, where two particles behave like a single unit even when they are separated. Their results have cleared the way for new technology based upon quantum information. ...

For a long time, the question was whether the correlation was because the particles in an entangled pair contained hidden variables, instructions that tell them which result they should give in an experiment. In the 1960s, John Stewart Bell developed the mathematical inequality that is named after him. This states that if there are hidden variables, the correlation between the results of a large number of measurements will never exceed a certain value. However, quantum mechanics predicts that a certain type of experiment will violate Bell’s inequality, thus resulting in a stronger correlation than would otherwise be possible.

It was not much of a question. John von Neumann and others convinced everyone that it was impossible in 1931.

These Bell test experiments proved that quantum mechanics could not be replaced by a classical theory. Some say that they are the most profound results in all of science, but they really just confirm what was discovered around 1930.

Bell, Clauser, and others were hoping to disprove QM. That certainly would have been a big deal, but the experiments only confirmed QM.

Many others say that the experiments proved that the world is random and nonlocal, and showed the possibility of quantum cryptography and quantum computing. The Nobel citation conspicuously avoids endorsing any of these ideas.

Indeed, the overwhelming empirical evidence in the realms of atomic and optical physics was, to most practitioners, confirmation of the potent predictive power of quantum mechanics. Thus, to them, the experiments of Clauser and Aspect came as no surprise. Others saw them as fundamental discoveries about the nature of physical reality, providing an ultimate verification of quantum mechanics in a regime that is far removed from classical laws and reasoning.

This year’s Nobel prize is for experimental work.

Just for experimental work, and not for any philosophical ramblings about locality or randomness or reality.

It does acknowledge several researsch topics:

Today, quantum technology refers to a very broad range of research and development. As an illustration we mention that the EU financed Quantum Technology Flagship [30] lists four main areas: quantum computing, quantum simulation, quantum communication and quantum metrology and sensing. In all of these areas quantum entanglement plays a fundamental role. This is an inappropriate venue to survey this vast landscape of innovative research.

But no prize for this stuff. It only says that Bell test experiments could make quantum key distribution more secure. Maybe so, but it is hard to see how QKD could ever be as secure as the non-quantum methods that are used all over the world today.

Here is the NY Times account:

The laureates’ research builds on the work of John Stewart Bell, a physicist who strove in the 1960s to understand whether particles, having flown too far apart for there to be normal communication between them, can still function in concert, also known as quantum entanglement.

According to quantum mechanics, particles can exist simultaneously in two or more places. They do not take on formal properties until they are measured or observed in some way. By taking measurements of one particle, like its position or “spin,” a change is observed in its partner, no matter how far away it has traveled from its pair.

No, QM does not teach that a particle can exist in two places at once. That is just an interpretation. And no, measuring an entangled particle does not cause a change to be observed in its partner. That is nonlocality spookiness that the Nobel citation managed to avoid. There is no action-at-a-distance.

Measuring one particle can affect what is predicted about the other. That is called entanglement. It is also true about classical (non-quantum) systems. The difference is the strength of the correlation. That is what Bell showed.

Bell later falsely claimed that he proved nonlocality. The Nobel citation politely avoids mentioning this.