What is time? Nathan Nelson/Flickr

There is a limit to how well we can measure time, with quantum mechanics and general relativity resulting in a "blurred" flow, scientists have discovered.

In a study published in the journal PNAS, a team from the University of Vienna and the Institute of Quantum Optics and Quantum Information were looking at what happens to time when you factor a clock into the mix.

Normally, you would not think clocks affect space or time – and that time can be measured accurately at different points in space. But this is not the case if you are a theoretical physicist.

Quantum mechanics says that there is a fundamental limit to how precise we can measure physical properties of a pair – like the time of a clock and energy. This sort of works on an inversely proportional scale, so the more precise the clock, the more uncertain its energy becomes. This means the most precise clock would have limitless uncertainty relating to its energy.

The next thing to consider is Einstein's theory of general relativity, which says the flow of time is altered by masses or sources of energy. As a result, time runs slower near an object of large energy, and faster when it is near an object with a smaller energy.

So what happens when you combine these principles? Researchers found that when you place clocks next to each other, they would disturb each other. This led to a 'blurred' flow of time, meaning there is a fundamental limit to our measurements of it. The more precise a clock, the more it blurs the flow of time of the other clocks near it.

"Based only on the assumption that both principles hold in this situation, we show that the clocks necessarily get entangled through time dilation effect, which eventually leads to a loss of coherence of a single clock. Hence, the time as measured by a single clock is not well defined," they wrote.

Lead author Esteban Castro added: "Our findings suggest that we need to re-examine our ideas about the nature of time when both quantum mechanics and general relativity are taken into account."