What came first: the chicken or the egg?
This question was first posed by philosophers in Ancient Greece to describe the problem of determining cause-and-effect, and a quandary we're still not able to definitively answer many years later.
Well, that could all be about to change, according to a team of physicists from The University of Queensland and the NÉEL Institute.
The researchers say they can use quantum physics to prove that both the chicken and the egg can come first.
Dr Jacqui Romero from the ARC Centre of Excellence for Engineered Quantum Systems attempted to describe the theory and explained that in quantum physics, cause-and-effect is not always as straightforward as one event causing another.
"The weirdness of quantum mechanics means that events can happen without a set order," she said.
"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, but in our experiment, both of these events can happen first."
Romero added that this is called "indefinite causal order" and it isn't something that we can observe in our everyday life."
To observe this effect in the lab, the researchers used a setup called a photonic quantum switch.
The University's Dr Fabio Costa added that with this device the order of events - known as transformations on the shape of light - depends on something called "polarisation".
"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," he added.
"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."
The researcher's theory was published in full by the American Physical Society in the Physical Reviews Letters journal.
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