Although there are many variables in life, there’s one metric by which our existence is strictly measured: time.
We think of it as rigid, smooth, and unidirectional – the arrow of time flies straight and true, and all we can do is go where it leads.
But what if time is a little more loosey-goosey than our experience of it suggests? What if it harbors a hidden quantum nature?
In a new paper, a team of physicists has shown how optical clocks – a highly precise type of atomic clock that uses optical light frequencies instead of microwave signals – might be used to demonstrate the quantum nature of time. In turn, this could help us understand the entire mysterious nature of time itself.
“It turns out, there are deeper facets of time that no one has ever experienced, and that have never been measured either,” physicist Igor Pikovski of Stevens Institute of Technology in the US told ScienceAlert.
“According to quantum theory, there can be instances where time does not simply change steadily at one rate. Instead, there are ‘many times in superposition’, i.e., it passes at different rates at the same time.
“This means in practice that a single clock would record several different times, not just a single one as we are usually used to. This has never been observed before, but we show that this is something that modern ion-clocks could now detect.”
For centuries, time has been considered absolute, as defined by Sir Isaac Newton. He described it as a universal constant, an independent facet of objective reality that could not be affected by external influences.
Then along came Albert Einstein, slyly poking the stick of relativity in the spokes of the Newtonian bicycle. His new physics frameworks showed that time is relative, and can move faster or slower depending on motion and gravity.
“There is no universal time, and only what we call ‘proper time’: Each observer records their own time, and it can differ,” Pikovski explained.
“This is what we work with, namely that the flow of time changes with velocity and position. The ‘twin paradox’ is a typical example of relativistic time according to Einstein, where a twin takes a round-trip in a rocket, and when he comes back he is younger than his other twin who aged more staying on Earth.”
Time dilation is a relativistic effect and, therefore, well understood.
What has not yet been probed experimentally is how time might behave in a quantum regime, on scales where relativity alone is no longer sufficient to describe how the Universe behaves, and quantum theory comes into play.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Even in quantum theory, however, time is still usually treated as a classical phenomenon ticking along in a straight line in the background.
“One of the most important challenges of modern physics is to find a quantum theory of gravity,” Pikovski explained.
“In such a theory, we expect many of the otherwise classical concepts like time and gravity to be described by something fundamentally quantum. So we know that time as we describe it today cannot be the final story – something is missing when quantum theory comes into the picture.”
In their paper, Pikovski and his colleagues propose ways in which ultra-precise optical clocks, ticking to the oscillating beat of atoms excited by lasers, could be used to probe quantum temporal phenomena.
These include temporal superposition, in which overlapping times can exist simultaneously, and entanglement, where time and motion can become linked to influence each other’s behavior.
“Entanglement and superposition are hallmarks of quantum behavior,” Pikovski told ScienceAlert.
“Our work shows that even time itself could have such quantum hallmarks, which is not what is typically assumed in quantum physics.”
In practice, this could mean a single clock registering more than one time at once, separated by unimaginably small fractions – on the order of tens-of-attoseconds intervals that only an optical atomic clock is precise enough to measure.
Atomic clocks are already precise enough to measure tiny effects of relativity, such as time dilation; for example, if you lift one clock just a few inches above the altitude of another, the minuscule difference in Earth’s gravity between the two is enough to create a dilation effect detectable in the clocks.
According to the work of Pikovski and his colleagues, optical clocks may be precise enough to observe quantum effects, too.
The team proposes using a quantum technique known as “squeezing“, which can amplify tiny fluctuations in a system. In this case, it could enhance the quantum behavior of the atoms inside the clock, making the strange effects on time more visible.
Some of these effects could be detectable with current technology, while others are still too small and fragile. However, those that are within reach are worth pursuing.
The techniques proposed by the researchers could yield the first experimental evidence that time itself can behave quantum mechanically.
That would give physicists a new way to probe the intersection of relativity and the quantum realm, as well as new insights into the very nature of time.
Related: This New Clock Is So Precise It Could Soon Redefine The Second
“I think it can give us hints, and experimental input, on how our everyday notions of reality are misleading. Quantum theory is not just bizarre, it also implies a very different fundamental structure of the universe that is at odds with everyday experience,” Pikovski said.
“Einstein famously remarked: ‘Is the Moon there when nobody looks?’ He made this remark to highlight the bizarre predictions of quantum mechanics.
“If time itself inherits these quantum features, i.e., time can be in superposition when nobody looks, this to me would be a fascinating glimpse into the strange inner workings of nature, and give hints towards new frontiers of fundamental physics.”
The paper has been published in Physical Review Letters.
