basis for their measurement settings. This experiment pushed the timeframe for when the settings could have been mutually determined to at least 7.8 billion years in the past, a substantial fraction of the superdeterministic limit (that being the creation of the universe 13.8 billion years ago). The 2019 PBS Nova episode Einstein's Quantum Riddle documents this "cosmic Bell test" measurement, with footage of the scientific team on-site at the high-altitude Teide Observatory located in the Canary Islands. Loopholes Though the series of increasingly sophisticated Bell test experiments has convinced the physics community in general that local realism is untenable, local realism can never be excluded entirely. For example, the hypothesis of superdeterminism in which all experiments and outcomes (and everything else) are predetermined cannot be tested (it is unfalsifiable). Up to 2015, the outcome of all experiments that violate a Bell inequality could still theoretically be explained by exploiting the detection loophole and/or the locality loophole. The locality (or communication) loophole means that since in actual practice the two detections are separated by a time-like interval, the first detection may influence the second by some kind of signal. To avoid this loophole, the experimenter has to ensure that particles travel far apart before being measured, and that the measurement process is rapid. More serious is the detection (or unfair sampling) loophole, because particles are not always detected in both wings of the experiment. It can be imagined that the complete set of particles would behave randomly, but instruments only detect a subsample showing quantum correlations, by letting detection be dependent on a combination of local hidden variables and detector setting. Experimenters had repeatedly voiced that loophole-free tests could be expected in the near future. In 2015, a loophole-free Bell violation was reported using entangled diamond spins over a distance of and corroborated by two experiments using entangled photon pairs. The remaining possible theories that obey local realism can be further restricted by testing different spatial configurations, methods to determine the measurement settings, and recording devices. It has been suggested that using humans to generate the measurement settings and observe the outcomes provides a further test. David Kaiser of MIT told the New York Times in 2015 that a potential weakness of the "loophole-free" experiments is that the systems used to add randomness to the measurement may be predetermined in a method that was not detected in experiments. Detection loophole A