Which came first, the chicken or the egg? The debate has been raging for what feels like forever, as much in the scientific community as among fans of armchair philosophy. Physicists have finally given their verdict on this age-old question.
Aristotle was one of the first great thinkers to have tackled this existential problem. No less than 2340 years after his death, researchers at Queensland University in Australia and at the Néel Institute in Grenoble have continued the discussion. In a study published in the journal Physical Review Letters, they give an answer which is very different from the one formulated by the philosopher from antiquity. The solution actually lies in quantum physics. Co-author of the study Dr Jacqui Romero, who belongs to the Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) stated:
The weirdness of quantum mechanics means that events can happen without a set order.
In quantum physics, the a-priori link between cause and effect is called into question, just like the chronological succession of events. Dr Romero explains:
This is called “indefinite causal order,” and it isn’t something that we can observe in our everyday life. Take the example of your daily trip to work, where you travel partly by bus and partly by train. Normally, you would take the bus then the train, or the other way round. In our experiment, both of these events can happen first.
And as you can’t make an omelette without cracking a few eggs, the researchers worked hard to find empirical proof of their concept. To do this, they conducted an experiment which, like a chicken’s beak, proved quite sharp. For this, they used a quantum light switch. It’s an optical instrument in which the order of events depends on the polarization of light, as Fabio Costa, a researcher at Queensland University, explains:
‘By measuring the polarisation of the photons at the output of the quantum switch, we were able to show the order of transformations on the shape of light was not set.’
This unexpected result concludes centuries of debate.
All eggs in the technology basket
The researchers aren’t going to stop there, as Fabio Costa explains:
‘This is just a first proof of principle, but on a larger scale indefinite causal order can have real practical applications, like making computers more efficient or improving communication.’
From now on, the chicken-and-egg paradox won’t cause anyone else to put up a squawk. At least not among fans of quantum science!