Scientists from Australia and France have subjected one of the most ancient philosophical questions about causation to a quantum experiment.
Initially, the topic of chicken and eggs was proposed by ancient Greek philosophers to determine cause and effect. Today, a team of physicists from the University of Queensland and the Louis Néel Institute have demonstrated that as far as quantum physics can be judged, both the chicken and the egg could appear simultaneously - the first. The research is published in the journal Physical Review Letters.
Dr. Jacqui Romera of the ARC Center of Excellence for Engineered Quantum Systems stated that in quantum physics, cause and effect is not always straightforward: one event does not necessarily cause another.
“The weirdness of quantum mechanics means that things can happen without following a certain order,” she explains. Take, for example, your daily commute to work, some of which you travel by bus and some by subway. First you go by bus and then by train, or vice versa. In our experiment, both of these events can occur first in the sequence. This is called an "indefinite causal order" and we have no way of observing it in everyday life."
To study this effect in the laboratory, the scientists used a setup known as a photonic quantum switch. Dr. Fabio Costa of the University of Queensland argues that the order of events in this device - transforming the shape of light - depends on the polarization of the photons.
“By measuring the polarization of photons at the exit from the quantum switch, we were able to demonstrate the uncertainty in the order of transformations of the shape of light,” he says. "This is just a proof of principle, but on a large scale, there are real practical uses for undefined causality, such as improving the performance of computers or improving communications."
Vladimir Guillen