(ORDO NEWS) — In his theory of general relativity, Einstein predicted something called time dilation: the notion that two clocks under two different gravitational pulls would always run at different speeds.
Since then, this effect has been observed in many experiments, but now scientists have captured it on the smallest scale that has been observed so far.
The result was achieved using ultra-precise atomic clocks spaced just a millimeter (0.04 inches) apart – about the width of a sharp pencil tip. After collecting data for 90 hours, the team obtained readings that are 50 times more accurate than all previous similar measurements.
And, of course, the smaller and more precise the scale, the more we rely on quantum mechanics to explain what is happening. The researchers hope their new readings pave the way for new insights into how the curvature of spacetime – what we perceive as gravity – affects the characteristics of particles according to quantum physics.
“The most important and exciting result is that we can potentially relate quantum physics to gravity, for example, explore complex physics where particles are distributed in different places in curved space-time,” says physicist Jun Yeh of the University of Colorado at Boulder.
In this experiment, the researchers used what is known as an optical lattice, a network of laser light used to hold atoms in place so they can be observed. This technique is used in the latest generation of atomic clocks, providing more accurate timekeeping using laser light waves, and these gratings can also be used for quantum simulations.
In this case, two atomic clock readings were obtained from the same cloud of atoms in a tightly controlled energy state. In fact, the atoms moved between two energy levels in perfect synchronization within 37 seconds, which is a record in terms of quantum coherence (that is, maintaining the stability of quantum states) – and this stability is very important for such measurements.
This allowed the scientists to take readings at two separate points, measuring the redshift in a cloud of about 100,000 ultracold strontium atoms. Redshift shows the change in the frequency of radiation of atoms in the electromagnetic spectrum – or, in other words, how fast the atomic clock is ticking.
Although the redshift difference at this tiny distance was only 0.00000000000000000000001 or so, this is in line with the predictions of general relativity. These differences can matter when you go to the scale of the entire universe, or even when you’re dealing with systems that need to be ultra-precise, like GPS navigation.
“This is a completely new game, a new mode in which you can explore quantum mechanics in curved space-time,” says Ye.
“If we can measure redshift 10 times better than now, we can see waves of all the matter of atoms in curved space-time. Being able to measure time differences on such tiny scales could allow us to detect, for example, that gravity breaks quantum coherence, which may underlie why our macroscale world is classical.”
Part of the reason time dilation research is so interesting is that it points the way to atomic clocks that will become even more accurate in the future, giving scientists a blueprint that can be refined to make measurements on smaller and smaller scales.
Atomic clocks have come a long way in the last few decades and there is still a lot to be done.
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