New Clocks Measure Earth’s Gravity and Perhaps Dark Matter

This sounds crazy, but with two or more very accurate clocks scientists can measure time well enough to see variations in gravity at the earth’s surface. A clock as a gravity meter seems impossible … until you accept one of the weird things about our universe that Albert Einstein worked out: gravity slows time. This effect, called gravitational time dilation, has been experimentally confirmed by tests of Einstein’s theory of general relativity. It is a true strange fact that gravity due to mass slows time in predictable and repeatable ways. Said another way, mass bends the space-time. Hard to believe, but it seems to be confirmed.

The higher the gravitational potential (the farther the clock is from the source of gravitation), the faster time passes. Albert Einstein originally predicted this effect in his theory of relativity and it has since been confirmed by tests of general relativity.

A new type of atomic clock using ytterbium atoms is 100 times more accurate than our current standard atomic clocks.

Experimental atomic clocks at the National Institute of Standards and Technology (NIST) have achieved three new performance records, now ticking precisely enough to not only improve timekeeping and navigation, but also detect faint signals from gravity, the early universe and perhaps even dark matter.

… Einstein’s theory of relativity predicts that an atomic clock’s ticking, that is, the frequency of the atoms’ vibrations, is reduced — shifted toward the red end of the electromagnetic spectrum — when operated in stronger gravity. That is, time passes more slowly at lower elevations.

While these so-called redshifts degrade a clock’s timekeeping, this same sensitivity can be turned on its head to exquisitely measure gravity. Super-sensitive clocks can map the gravitational distortion of space-time more precisely than ever. Applications include relativistic geodesy, which measures the Earth’s gravitational shape, and detecting signals from the early universe such as gravitational waves and perhaps even as-yet-unexplained “dark matter.”

NIST’s a clocks now exceed the conventional capability to measure the geoid, or the shape of the Earth based on tidal gauge surveys of sea level. Comparisons of such clocks located far apart such as on different continents could resolve geodetic measurements to within 1 centimeter, better than the current state of the art of several centimeters. …

Among the improvements in NIST’s latest ytterbium clocks was the inclusion of thermal and electric shielding, which surround the atoms to protect them from stray electric fields and enable researchers to better characterize and correct for frequency shifts caused by heat radiation.

The ytterbium atom is among potential candidates for the future redefinition of the second — the international unit of time — in terms of optical frequencies. NIST’s new clock records meet one of the international redefinition roadmap’s requirements, a 100-fold improvement in validated accuracy over the best clocks based on the current standard, the cesium atom, which vibrates at lower microwave frequencies.

NIST is building a portable ytterbium lattice clock with state-of-the-art performance that could be transported to other labs around the world for clock comparisons and to other locations to explore relativistic geodesy techniques.

Via SciDaily

New ytterbium clocks may help scientists find dark matter.

Dark matter is thought to make up some five sixths of all matter in the universe. Yet incredibly sophisticated projects ranging from the most powerful atom smasher ever built to vats of chilly liquid xenon have failed to find a trace of it. But now some scientists are hoping atomic clocks, the most precise timekeepers ever made, could be used to help explain this elusive phenomenon.

Many physicists believe dark matter is an invisible substance whose predicted gravitational effects on known matter would help explain a variety of cosmic mysteries, such as why galaxies can spin as fast as they do without flying apart. Despite its apparently colossal importance to the very structure of the universe, however, no one knows anything for certain about what it might be composed of or where it came from. On Monday a group of physicists in Poland published a study in Nature Astronomy that suggests fluctuations in the rate that an atomic clock “ticks” might help reveal how apparent dark matter can influence known matter.

Scientists have largely ruled out all known particles as possible explanations for dark matter. This suggests it may comprise a kind of particle that falls outside the Standard Model of physics, which is currently our best working description of the subatomic world. Another possibility is that dark matter is not made of particles at all; rather it is a field that permeates space much like gravity does. 

Via SciAm

I guess they ruled out microscopic space dust? That’s been my best guess for years about what dsrk matter is.

Yet another option is that Einstein was wrong and that our model of gravity is flawed. In one alternative theory, gravity is not a force, but rather the emergent result of entropy. In this scenario all dark matter in the universe vanishes… because it never existed in the first place. Time will tell?

I find it an interesting coincidence (as in “points to a simulation”) that I, Xeno, find myself writing about ytterbium being used to make the most accurate time measurements on our planet so far and the element ytterbium comes in part from mining of Xenotime, a sometimes radioactive rare-earth phosphate mineral. Did xenotime even exist before I started writing this? (Many worlds hypothesis.) I never heard of it until today. Very funny, universe.

What time is it?

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