So was it the chicken or the egg?

Physicists have finally answered the question of which came first, the chicken or the egg?

Using two of the most powerful and complex theories of modern physics, quantum mechanics and general relativity, a paper published in Nature Communications reveals that the answer is: both. Or neither.

“The notion of time order is not predefined. Time does not exist out there independent of our experiments,” says lead author Magdalena Zych, from the University of Queensland in Australia.  

Although the answer may be surprising for chickens, quantum physicists are familiar with the concept of superpositions of states: before it is measured, an object can be in a number of possible states at once. 

This can apply to the quantum spin of an electron, the polarisation of a photon, or crucially for this thought experiment, the position of an object, such as a chicken.

Normally a chicken’s watch would tick at the same speed over here as it would over there. But the twist comes when you add the General Theory of Relativity: Einstein’s theory that says that dense objects such as black holes warp both space and time. 

So, if you have a black hole near your chicken, time will slow down, meaning the egg probably came first.

However, the authors threw a cat amongst the chickens by imagining a black hole in a superposition of locations; for example, one near the chicken, one near the egg. 

In other words, there are two possible states co-existing, one in which the chicken’s watch ticks slowly, and another in which the egg’s watch ticks slower.

“It gives a new insight into the nature of time,” says Zych’s colleague and co-author Fabio Costa.

“In order to speak about time, you need to take a concrete approach: you cannot say that time is well defined. It’s quite a profound result.”

Costa conceded that the concrete example used in their thought experiment, a superposition of planets near starships (no chickens were mentioned), was unlikely to ever be realised. 

However, he said there could be systems such as quantum computers that would benefit from the new finding.

The equations for quantum mechanics and general relativity are famously incompatible in some situations. However, devising a concrete scenario was the key to solving the equations, says Zych.

“We were able to overcome some mathematical obstacles without having to resort to mathematical formalisms such as loop quantum gravity or string theory.” 

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