Physics 7 May 2021

By Leah Crane

Keeping time accurately comes with a price. The maximum accuracy of a clock is directly related to how much disorder, or entropy, it creates every time it ticks.

Natalia Ares at the University of Oxford and her colleagues made this discovery using a tiny clock with accuracy that can be controlled. The clock consisted of a 50-nanometre-thick membrane of silicon nitride, vibrated by an electric current. Each time the membrane moved up and down once and then returned to its original position, the researchers counted a tick, and the regularity of the spacing between the ticks represented the accuracy of the clock.

They found that as they increased the clock’s accuracy, the heat produced in the system grew, increasing the entropy of its surroundings by jostling nearby particles. “If a clock is more accurate, you are paying for it somehow,” says Ares.

In this case, you pay for it by pouring more ordered energy into the clock, which is then converted into entropy. “By measuring time, we are increasing the entropy of the universe,” says Ares. The more entropy there is in the universe, the closer it may be to its eventual demise. “Maybe we should stop measuring time.” The scale of the additional entropy is so small, though, that there’s no need to worry, she says.

The increase in entropy in timekeeping may be related to the “arrow of time”, says Marcus Huber at the Austrian Academy of Sciences in Vienna, who was part of the research team. It has been suggested that the reason that time only flows forward, not in reverse, is that the total amount of entropy in the universe is constantly increasing, creating disorder that cannot be put in order again.

SNIP