One of the themes of the history of science is that topics that were obscure in the past “suddenly” become critically important. A current example is the esoteric science that allows quantum computing.
Quantum computing relies on the fact that a pair of particles can be entangled in a singlet state and until they are measured the state is a probability function – the actual state is only concrete when an observation is made. This is different from classical physics which would say that each particle has its own state when it is created (a “hidden variable”).
For example, when a photon of light goes through a beam splitter it can turn into two photons with opposite polarisations. Classical physics would say that each photon has its polarisation stamped on it at birth (“hidden variable”), quantum physics would say that it polarisation is only decided when it is measured (“wave function collapse”).
Einstein did not like quantum mechanics because in this example the measurement of one photon’s polarisation caused the wave function to collapse and instantaneously (faster than light) the polarisation of the second photon is decided. He called this “spooky action at a distance”.
This was all very theoretical until 1964 when Bell worked out a way of detecting whether there were hidden variables.
The next step in my journey to greater understanding of this topic is to understand how Bell’s Theorem is tested experimentally. I may post on this in future.