New experience shows that the more energy a clock consumes, the more accurate its timing.
Clocks permeate all aspects of life, from atomic clocks that underpin satellite navigation to cell clocks inside our bodies. All of them consume energy and give off heat. A kitchen clock, for example, does this by using its battery. Generally, the more precise clocks require the most power, suggesting a fundamental link between power consumption and accuracy. This is what an international team of scientists from Lancaster, Oxford and Vienna set out to test.
To do this, they built a particularly simple clock, consisting of an ultra-thin vibrating membrane, several tens of nanometers thick and 1.5 millimeters in length, incorporated into an electronic circuit. Each oscillation of the membrane generated an electrical tic. The ingenious aspect of this design is that it is powered simply by heating the membrane, while the full flow of energy through the clock can be measured electrically.
Scientists have found that the more heat they provide, the more accurately the clock runs. In fact, the accuracy was directly proportional to the heat released. To make the clock twice as accurate, they had to provide twice as much heat.
The experimental team consisted of Dr Edward Laird from Lancaster University, Professor Marcus Huber from the Atominstitut, TUWien, Dr Paul Erker and Dr Yelena Guryanova from the Institute for Quantum Optics and Quantum Information (IQOQI) , and Dr Natalia Ares, Dr Anna Pearson and Professor Andrew Briggs of Oxford.
Their study, published in Physical examination X, is the first time that a measurement has been made of the entropy – or heat loss – generated by a minimum clock.
Understanding the thermodynamic cost involved in timing is a central step in the development of future technologies, and understanding and testing thermodynamics as systems approach the quantum realm.
It also shows a similarity between the operation of a clock and a steam engine. With a steam engine, there is a fundamental constraint on the amount of heat we must provide to do the desired amount of work. This constraint is the famous second law of thermodynamics which is at the heart of modern engineering. What this experiment suggests is that clocks, like motors, are constrained by the Second Law, their output being precise ticks instead of mechanical work.
Dr Edward Laird of Lancaster University said: “The subject of thermodynamics, which incorporates the most basic principles of nature, tells us that there are two types of machines that we cannot operate without releasing The first is the mechanical motor, which releases heat to run, and the other is computer memory, which releases heat when it rewrites itself. This experience – in conjunction with others work – suggests that clocks are also limited by thermodynamics. It also poses an intriguing question: are all clocks possible limited in this way, or is it just a property of those we have studied? “
Interestingly, many everyday clocks have an efficiency close to what scientists’ analysis predicts. For example, their formula predicts that a wristwatch with an accuracy per tick of one part in ten million must consume at least one microwatt of energy. In fact, a basic wristwatch usually only consumes a few times that amount. The laws of thermodynamics, discovered in the 19th century, still find new applications today.
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