{"id":3954,"date":"2022-03-30T22:00:00","date_gmt":"2022-03-30T22:00:00","guid":{"rendered":"https:\/\/modernsciences.org\/staging\/4414\/?p=3954"},"modified":"2022-03-15T09:10:25","modified_gmt":"2022-03-15T09:10:25","slug":"physicists-just-measured-the-effects-of-time-dilation-down-to-a-millimeter","status":"publish","type":"post","link":"https:\/\/modernsciences.org\/staging\/4414\/physicists-just-measured-the-effects-of-time-dilation-down-to-a-millimeter\/","title":{"rendered":"Physicists Just Measured the Effects of Time Dilation Down to a Millimeter"},"content":{"rendered":"\n

True to Albert Einstein\u2019s calculations all the way back in 1915, gravity does indeed have an effect on the passage of time. To be precise, the stronger gravity distorts spacetime, the slower the passage of time becomes. Scientists have been able to measure the effects of what\u2019s known as time dilation<\/em> within the scales of thousands of kilometers, but a recent study from a collaboration between the National Institute of Standards and Technology<\/a> (NIST) and the University of Colorado Boulder<\/a> (UCB) just managed to whittle down our measurements\u2014all the way down to its effects across a single millimeter.<\/p>\n\n\n\n

Humans may not feel the effects of time dilation in everyday life as it\u2019s far too small to be perceived, but it\u2019s definitely there; for that reason, your feet age slower than your head, and someone living on the uppermost penthouse of an apartment ages faster than someone living closer to the lobby down below. This is because the gravity of the Earth itself affects time around it, and satellites in orbit need to take this into account when they help let you know how far you are from your current GPS destination.<\/p>\n\n\n\n

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Spacetime is described as a \u201cfabric\u201d that distorts in the presence of objects with large masses, like planets and our own Sun. Distortions in this \u201cfabric\u201d are likened to ripples in a pond when a stone is thrown onto it, and is illustrated above in an artist\u2019s impression of two neutron stars colliding. (ESA, 2017)<\/figcaption><\/figure><\/div>\n\n\n\n

Now, recent research published in the journal Nature<\/em><\/a> managed to give us our most precise measurement of time dilation to date. The remarkable feat was the product of the JILA collaboration<\/a> between NIST and UCB.<\/p>\n\n\n\n

\u201cThe most important and exciting result is that we can potentially connect quantum physics with gravity, for example, probing complex physics when particles are distributed at different locations in the curved space-time,\u201d said NIST\/JILA Fellow Jun Ye. \u201cFor timekeeping, it also shows that there is no roadblock to making clocks 50 times more precise than today\u2014which is fantastic news.\u201d<\/p>\n\n\n\n

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Pictured above is NIST-7, the atomic clock used by NIST\u2014and by consequence the United States\u2014as their time and frequency standard between 1993 and 1999. The setup was composed of a caesium (Cs) beam clock. (NIST, 1993)<\/figcaption><\/figure><\/div>\n\n\n\n

Of course, the details surrounding this landmark study stretch far beyond just pulling out your nearest stopwatch and watching the seconds pass. The team needed the help of atomic clocks, which themselves make use of atoms that interact with specific electromagnetic frequencies as they transition between different energy levels.<\/p>\n\n\n\n

Ye and the team measured the frequency shifts between the top and bottom of their own atomic clock, which contained 100,000 ultracold strontium (Sr) atoms in an \u201catomic cloud\u201d as they switched between two energy states. To do so, the team had to keep the ticking of these atoms in the \u201ccloud\u201d synced for a record total of 37 seconds.<\/p>\n\n\n\n

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JILA also created another laser-based technology called the extreme ultraviolet (EUV) frequency comb, which was used to probe UV wavelengths. (NIST, 2012)<\/figcaption><\/figure><\/div>\n\n\n\n

These atoms were also loaded into what was called an optical lattice<\/em>, which the team described in the NIST press release<\/a> as \u201ca stack of pancakes created by laser beams<\/a>.\u201d From there, they used precise imaging techniques to measure the differences between the atomic ticking of the upper and bottom portions of the \u201cpancake stack.\u201d<\/p>\n\n\n\n

It was there that they measured a difference between the two regions, which was in turn described as a redshift<\/em> across the atomic cloud. (This is analogous to how an ambulance\u2019s siren changes pitch\u2014and hence sound frequency\u2014depending on whether it\u2019s moving towards or away from you.) The measured redshift was in the realm of 0.0000000000000000001\u2014unimaginably small to us humans, but nevertheless measurable.<\/p>\n\n\n\n

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