Nature Park (IMAGE) University of Vienna Caption Physicists use an interferometer to test whether standard quantum mechanics is correct, or whether a more complex version is required. They used the interferometer to send photons around a loop in opposite directions. In this way, photons travelling in one direction interact with objects inside the loop in one order, while photons travelling the opposite direction interact with objects in the opposite order. The physicists were interested whether the order of the interaction mattered, as predicted by alternative versions of quantum mechanics. Credit Copyright: MSc. Jonas Schmöle, Faculty of Physics, University of Vienna Usage Restrictions The image may only be used with appropriate caption or credit. License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.