Sunday , May 16 2021

This new atomic clock is so precise Our ability to measure gravity limits its accuracy

NIST Optical Atomic Clock is the most accurate time storage device ever made. Picture: NIST

Researchers at the National Institute of Standards and Technology (NIST) have developed an atomic clock that is so precise that our Earth Gravity models are not accurate enough to continue. As stated in the paper published this week in Nature , the atomic clock could pave the way for an unprecedented map of the way Earth's gravity distorts the space time and even sheds light on the development of the early universe.

"The clock performance level is such that we actually do not know how to explain it well enough to support the performance level that the clock achieves," said Andrew Ludlow, a NIST physicist, and the project leading to the new atomic clock organization, told me on the phone. "Right now the cutting-edge techniques are not good enough, so we are limited by how well we understand gravity in different parts of the earth."

However, before it dives into a clay stronghold of what Ludlow and his colleagues in NIST have done, it will help to have some background for the nature of time and atomic clocks.


Regardless of what your Zimmer College said while hitting the bong, as many scientists are worried about, time is measuring periodic occurrences. In other words, time is something that measures it, otherwise known as a clock. Quite a lot that happens at regular frequencies can be considered as a clock, such as swinging the pendulum, the rotation of the Earth around its axis or the philosopher Emmanuel Kant, who passes the morning strolling through the neighborhood.

Apparently, not all watches are created equal. Each clock varies with its accuracy (how much its oscillation frequency deviates from a baseline) and the time scale. If you need to measure a five-minute passage, using the Earth's rotation as a clock will not be particularly useful. Also, if you have never tilted your watch, it will gradually become less accurate over time, due to minor imperfections in the mechanics.

Most of us are dealing with time limits ranging from years to seconds, which do not require incredibly accurate clocks. However, for scientists working on the bloody edge of physics, they require much more precise measurements over time. Fortunately, nature came endowed with incredibly precise clocks of its own in the form of a transition to atomic energy.

The electrons orbiting the nucleus of atom at certain stable levels of energy that depend on the electrical properties of the nucleus. These orbits can be changed by adding energy to the system, which causes electrons to temporarily descend to a higher energy level and emit electromagnetic radiation during the transition. Different types of atoms can absorb energy at different wavelengths and this function is used to create the most accurate watches in the world.

Read more: Why Nuclear Clocks will be the most accurate clocks on Earth

The first atomic clock was created in 1955 and used the energy transition of one electron in the cesium-133 atom as the reference frequency. Atoms of cesium-133 absorb energy at wavelengths of 3.2 cm, which means that the wave oscillates to frequency of 9,192,631,770 cycles per second. When cesium-133 atoms are affected by microwaves at this frequency, it causes one of the farthest electrons of the atom to rapidly cross between the energy states of the same rate. In this case, the transition of electrons between a high and low energy state over 9 billion times per second is analogous to a swift swing pendulum in a conventional clock. In fact, the transition of the cesium-133 electron was used formally defined the length of the second in 1967.

Today, four atomic clocks can be found on each of the 24 GPS satellites that orbit around the Earth and are used to synchronize time in our mobile phones and billions of other internet connected devices. They are also used to measure the mean sea level, which is used to understand the way our planet enhances the space time. The knowledge of this information is important for the calibration of the atomic clock based on space itself, but despite the accuracy of these clocks, NIST has an atomic clock that only deviates for one second every 200 million years – there is always room for improvement.

In this respect, the new atomic clock of NIST has been overcome. It is so precise that our current Earth Gravity models can not continue with that. Fortunately, the new clock will help change that.

Andrew Ludlow in the lab.

Andrew Ludlow is working on the atomic clock at the NIST laboratory. Picture: NIST


This is the most wanted question, but it is also one of the most difficult for physicists to answer. The reason for this, as Einstein discovered, is that time is not absolute. On the contrary, the time passes is relative. It depends on the observer's reference frame, which is influenced by things like their speed and the gravity of gravity in their reference frame. For example, a person near a strong gravitational field, such as a black hole, will experience time to move slower than a person standing on the surface of the Earth.

People experience time with macro days, hours, minutes – and in everyday life, we never move fast enough or travel in a sufficiently strong gravity field to notice a change in how fast or slow the time moves on these scales. However, when I climb the stairs every night in my apartment, time is acceleration whether I notice it or not.

"It's a small effect," Ladlow said. "It's kind of nasty that it's real, but it's."

Read more: The energy war in the Balkans has overshadowed the European clocks in five minutes

With each step I climb, I'm moving away from the center of gravity on Earth, which means that the effect of gravity on the frequency of what an oscillating thing I use as a clock decreases. Physicists calculated how much gravity affects time based on how high the clock is above the surface of the Earth and found that it is 1.1 quintiles per second for each vertical centimeter that the clock is raised above the surface. In other words, a second measured on the surface of the Earth actually takes 0.00000000000 seconds less for a clock one centimeter above the Earth and so on.

Of course, "the surface of the Earth" is shorthand, because this may mean wildly different things depending on where you stand. Dead End and Mount Everest top are the technical surface of the Earth, but one is 282 feet below the sea level and the other is 29,000 meters above sea level. To this end, the "sea level" is also in constant flux due to inflows of change.

To answer this problem, scientists see Earth as a "geoid". This is a hypothetical form of the Earth if the oceans were subject to the force of rotation and gravity on the Earth and were extended to all continents. This is, in fact, equivalent to taking the mean sea level throughout the Earth, which is done through a combination of ocean sensors and satellite data. When the geologist is visualized, it looks like this:

The geoid is great for measuring the heights of the Earth's surface to a high degree of accuracy, but it is a problem when it comes to creating ultra-precise clocks. The reason for this is because the Earth is not, in fact, a geoid and the differences in height cause significant gravitational effects on the timing. This is most pronounced in cases where atomic clocks are separated over long distances, such as those of GPS satellites.

Although scientists can explain these differences in Earth's gravity on the surface, also known as geopotential heights, using atomic clocks on satellites, they can only do so at a deviation of around 0.00 trillion000001 seconds, equivalent to a change in height of about 0.9 meters. The new atomic clock developed by NIST, however, is so precise that it can reduce the change of elements to only one centimeter, which is equivalent to a fault of only 1.4 parts in a quantile (one followed by 18 zeros).

According to Ludlow, this breakthrough was possible only because of the revolutionary nature of the clock itself. The atomic clocks used by NIST for this research consist of atoms of ytterbium suspended in a series of laser beams. Although potential latent in this technology has been known to physicists for years, only in recent years they have used technology to join these optical atomic clocks. Indeed, Ludlow said his recent breakthrough in his team is the culmination of the years spent in researching how to limit interference from things like electric and magnetic fields nearby.

Ladlou told me that the atomic clock NIST is a science wall and a door. It is a wall in the sense that it is so precise that current measurements of the geoid actually limit the accuracy of the atomic clock because it provides a geo-potential resolution in order of many centimeters, while their clock can reduce this geo-potential resolution to only one centimeter. On the other hand, the atomic clock of NIST is a door in the sense that it can be used to improve geodetic resolution several times. This would include distributing a few of these watches around the world and measuring small deviations in their time in order to get the highest card for constantly resolving how Earth's gravity distorts the length of time.

"If you had watches that you believed were correct at this high level, then you can use those watches as sensors of Earth's gravity potential, looking for changes in timing speed as you moved one of the clocks across different parts from Earth's gravity, "Ludlow told me.

Ludlow said that he and his NIST colleagues are currently working on prototypes for portable versions of their atomic clock that they can use to test this idea. Probably will be several years before they are distributed on Earth or in space, but meanwhile the NIST clock can be put in other ways, such as redefining the second to even greater precision.

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