A cool new paper appeared in Nature Physics this week and made a lot of waves (at least on my facebook feed).
In this paper titled “Quantum non-locality based on finite-speed causal influences leads to superluminal signalling” the authors show a method for testing if the “weird” effects of entanglement such as the violation of Bell inequalities can be explained using a faster then light source for exchanging information.
The main problem with these kinds of theories is that the usual Bell experiments can at best put a lower bound on the speed of exchanging this kind of information. The way to overcome this problem is to look at Bell violations in a 4 party system. The result of the paper is that one can perform a test that requires the speed of these causal influences to be infinite.