Physicists find quantum states of time induced by gravity

An international team led by researchers at the University of Queensland are trying to answer the question: What happens when an object that is massive enough to influence the flow of time is placed in a quantum state? 

This scenario, previously thought to be impossible by some physicists, has been described when the team combined elements of two theories describing the flow of time: general relativity and quantum mechanics. 

Lead author and UQ researcher Dr Magdalena Zych explained that in the first theory – general relativity – the presence of a massive object slows down the flow of time. 

Dr Zych said, “Imagine a pair of space ships, asked to fire at one another at a specified time while dodging the other’s attack.” 

“If either of the ships fires too early, it will destroy the other.” 

“A powerful enemy could use the principles of general relativity by placing a sufficiently massive object – like a planet – closer to one ship to slow the passing of time.” 

“The ship furthest away from that object will fire earlier, destroying the other ship.” 

This situation is made even more interesting by the second theory – quantum mechanics – that says any object can be in a state of superposition, which means it can exist in different states at the same time.

Dr Zych said, “If the enemy puts the planet into a state of quantum superposition, then there would also be a quantum superposition of time orders.”

This would mean there is a new way for the order of events to unfold.

UQ researcher Dr Fabio Costa said that this example of a superposition of planets may never be possible. 

Dr Costa said, “Current technology, however, can simulate the effects of quantum temporal order without using gravity. 

“Therefore, the study may be relevant for future quantum technologies, as quantum computers performing operations in a quantum order can outperform devices that operate in a fixed sequence.” 

The findings are published in “Bell’s theorem for temporal order”, M. Zych, F. Costa, I. Pikovski, and Č. Brukner, Nature Communications 10.1038/s41467-019-11579-x.

Media: Dr Magdalena Zych,, +61 475 058 394, +61 7 3346 7348

Major funding support

Australian Research Council

The Australian Research Council Centre of Excellence for Engineered Quantum Systems (EQUS) acknowledges the Traditional Owners of Country throughout Australia and their continuing connection to lands, waters and communities. We pay our respects to Aboriginal and Torres Strait Islander cultures and to Elders past and present.