Quantum Mechanics has the ability to surprise to owns and others. Recently, researchers have gone one step beyond performing a experiment that started 600 years ago, much before Plank, Einstein, or even Newton were born.
An international team has performed a Bell test, an experiment to shows the non-locality of quantum mechanics, closing all loopholes present in most of the previous experiments. They have put a new limit to the locality, placed in 600 light-years. They have used light coming from stars that are, at least, 600 years far from Earth.
This means that, if quantum mechanics is local, then the conditions of the experiment should have been stablished no less than 600 years ago.
Albert Einstein and others didn't like the fact that Nature is not defined until measured. He didn't like the fact that the outcome of a quantum experiment is determined randomly from all possible outcomes, but the liked less the fact that the state of a system is not defined is no one is looking, measuring the result.
John S. Bell found a mathematical expression to test whether a physical theory is local. By locality we understand that there is not any physical signal that can travel faster than light, as relativity implies. But there are experiments that allow to entangle two particles, forming a same quantum state. If those particles are sent away from each other, if the outcome is not defined, if there is not physical reality, you need to perform a measurement to create the outcome. Due to quantum relationships, the outcome of one particle will define the outcome of the other one, instantaneously!
Since Bell established his inequalities several experiments have been performed, agreeing with quantum mechanics. But until 2015, all of those experiments made one or more assumptions, in what have been known as loopholes. Closing all the loopholes simultaneously is not easy, but two independent groups did it (here) . What this international group (Austria, USA, Germany, China) has done is use the light from two distant stars as a source of randomness, essential for the experiment (the papers has been published at Physical Review Letters).
In the figure you can see the experimental scheme, where photons were sent from a central building, S, to two different buildings (A and B). The measurements settings were made using real-time observations of two distant stars (604 and 1930 light-years from Earth). The experiment assumes that the characteristics of the photons coming from the distant stars are independent and were established at the time of departure from the star, that nobody tampered them in their flight to Earth to affect the experiment.
Physicist, working in quantum optics and nonlinear dynamics in optical systems. Loves to communicate science.