In a study by the National Institute of Standards and Technology it was demonstrated that people age faster when standing a couple of steps higher on the staircase.

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WASHINGTON: Your head is billionths of a second older than your feet, said physicists who have measured the effects of time dilation over everyday scales, such as climbing stairs.

Decades ago, experiments proved the basic premise of Albert Einstein's theory of general relativity – that gravitational fields can warp time as well as space.

The gravitational pull from Earth decreases with the distance from the centre of the planet, time travels faster at high altitudes and slower at the surface. So back then, physicists sent an atomic clock into space on a rocket and comparing it to one kept behind on Earth.

‘Quantum logic clocks’ demonstrate theory

Now, technological progress has allowed physicists at the National Institute of Standards and Technology (NIST) in Boulder, Colorado to demonstrate the theory over everyday scales, such as climbing stairs and driving in cars.

In the study, published in Science, they showed how they measured the effect on a scale of about 33 centimetres to demonstrate how people age faster when standing a couple of steps higher on the staircase.

They used a pair of highly sophisticated experimental atomic clocks, dubbed ‘quantum logic clocks,’ which use laser lights to measure an electrically charged aluminium ion as it vibrates more than a million billion times a second.

Just like a tuning fork

One clock keeps time within one second in about 3.7 billion years, the study said, and the other is close behind.

The aluminium clocks can detect small relativity-based effects because of their extreme precision, the study said.

"You can think about it as how long a tuning fork would vibrate before it loses the energy stored in the resonating structure," said lead author James Chin-Wen Chou.

Testing the features of relativity

Although the results are infinitessimally small, they showed that climbing up steps will age you faster - adding up to about 90 billionths of a second over a 79-year lifespan.

In one of the experiments, scientists raised one of the clocks by elevating the laser table to a foot above the second clock. "Sure enough, the higher clock ran at a slightly faster rate than the lower clock, exactly as predicted," the study said.

The NIST team also studied another feature of relativity - that time passes more slowly when you move faster - but measured the effect at speeds such as a car travelling about 32 kilometres per hour, rather than on jet aircraft.