The NIST Optical Atomic Clock that is the most accurate time-saving device ever made. Image: NIST
Researchers of the National Institute of Standards and Technology (NIST) have developed an atomic clock that is so accurate that our Earth gravity models are not sufficiently precise to keep up with it. As described in the paper published this week in Nature . the atomic clock could open the way to creating an unprecedented map of how Earth's gravity distorts space time and even illuminates the development of the early universe.
"The performance level of the reported clock is such that we do not really know how to support it well enough to support the performance level that the clock achieves," Andrew Ludlow, a physicist at NIST and the project leads a new atomic clock organization, told me on the phone . "The current state of the art is not good enough and we are limited in how well we understand gravity in different parts of the Earth."
However, before you immerse yourself in the magical spell of what Ludlow and his colleagues at NIST have accomplished, however, they will help to gain some backgrounds of the nature of time and atomic clocks.
WHAT IS TIME AND HOW TO DO ATOMIC CANCER?
No matter what your roommate's college said while you were hitting bong, as far as most scientists are concerned, time is measuring periodic phenomena. In other words, time is what it measures, otherwise known as an hour. Much of what appears on regular frequencies can be considered an hour, such as a pendulum swing, Earth's rotation around its axis, or philosopher Emanuel Kant, who took his morning walk around the neighborhood.
Obviously, not all clocks are created equal. Each clock varies in terms of its accuracy (how much its oscillation frequency deviates from some basic line) and time scale. If you were to measure a five-minute pass, using Earth rotation as an hour would not be particularly useful. Likewise, if you never run the clock, it will gradually become less accurate over time due to the small imperfections in the mechanics.
Most of us deal with the time schedule from year to seconds, which does not require incredible precision watches. However, for scientists working on the vascular edge of physics, they require much more accurate measurement of time. Luckily, nature has experienced incredibly precise clocks in its own form of atomic energy transition.
Electrons orbits the core at certain stable energy levels that depend on the electrical properties of the core. These orbits can be changed by adding energy to the system, causing temporarily attracting electrons to higher levels of energy and emitting electromagnetic radiation during the transition. Different types of atoms are capable of absorbing energy at different wavelengths, and this feature is used to create the most accurate clocks in the world.
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The first atomic clock was created in 1955 and used the energetic transition of electrons to the cesium-133 atom as its reference frequency. Cesium-133 atoms absorb energy at wavelengths of 3.2 cm, which means that the wave oscillates at frequency of 9.192.631.770 cycles per secondWhen the cesium-133 atoms coincide with the microwaves at that frequency, it causes the only farthest electron atom to quickly switch between the energy states at the same rate. In this case, the electron that switches between high and low energy levels over 9 billion times per second, similarly to rapid swing in the conventional clock. In fact, the transition of cesium-133 electrons is used formally determine the length of a second in 1967.
Today, each of the 24 GPS satellites has Earth Orbit used for synchronizing time in our cell phones and billions of other Internet devices. They are also used to measure the median sea level, which is used to understand the way the gravity of our planet passes into space. Knowledge of this information is important for space-based atomic clock calibration, but in spite of the accuracy of these clocks – the NIST has an atomic clock that just shifts for one second every 200 million years – there is always room for improvement.
In that sense, the new atomic clock of NIST was transferred. So precise that our current models of Earth's gravity can not follow. Fortunately, the new clock will help change that.
Andrew Ludlow works at the atomic clock at the NIST lab. Image: NIST
WHAT TIME IS IT?
This is the majority of banal issues, but one of the most difficult for physicists to answer. The reason for it, as Einstein discovered, is that time is not absolute. Instead, the passage of time is relative. It depends on the observer's reference framework, influenced by things like their speed and the power of gravity within their reference frame. For example, a person near a strong gravitational field, such as a black hole, will feel the time to move slower than the person on the Earth's surface.
People experience time on macroscopic days, hours, minutes – and in our daily lives, we never move fast enough or travel to a sufficiently strong gravity field to notice a change in how fast or slow the time moves to those standards. Still, when I get upstairs at the apartment every night, time is is it quick to notice it or not.
"It's a small effect," said Ludlow. "It's very ridiculous that it's really, but it is."
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At every step of the climb, I move away from the Earth's gravity, which means that the gravitational effect on the frequency of each oscillating thing I use as a clock decreases. Physics has calculated just how much gravity affects time, depending on how high a clock is above the Earth's surface and found that for each vertical centimeter it is 1.1 quintillion seconds for each hour that is lifted above the surface. In other words, one second measured on Earth's surface actually takes 0.00 trillion or less seconds less than one centimeter above Earth and so on.
Of course, "Earth's surface" is stenographic because it can mean wild different things depending on where you are. The Death Valley and Mount Everest are the technical surface of the Earth, but one is 282 meters below sea level and the other is 29,000 feet above sea level. After all, the "sea level" itself is also in constant flux due to tidal changes.
To solve this problem, scientists imagine the Earth as a "geoid". It is a hypothetical form of Earth if the oceans were subject to only the forces of Earth's rotation and gravity, and spread across all continents. This is actually equivalent to taking the middle sea level across the Earth, which is achieved by a combination of sensors and satellite data. When visualizing a geoid, it looks like this:
The Geoid is great for measuring the height of the Earth's surface to a high degree of accuracy, but it poses problems when it comes to creating ultra-precise clocks. The reason is because the Earth is not really a geoid, and the differences in the elevation have significant gravitational effects on timing. This is most noticeable when atomic clocks are separated by large distances, such as those on GPS satellites.
Although scientists can count on those differences in Earth's gravity on the surface, also known as geopotential altitudes, using atomic clocks on satellites, they can only make up to about 0.00 billion trillion seconds, which equals a height change of about 0.9 feet. The new atomic clock developed by NIST is so accurate that it can change the height change to just a centimeter, which is equivalent to only 1.4 parts per quintile error (one followed by 18 zeros).
According to Ludlow, this breakthrough was possible only because of the revolutionary nature of the clock. The atomic clocks used by NIST for this research consist of a megawatt atom suspended in a series of laser beams. Although potential latencies in this technology have long been known to physicists for years, they have been using technology for the last few years to make use of these optical atomic clocks. Indeed, Ludlow said his team's recent breakthrough peaked years of research to limit disturbance of things like nearby electric and magnetic fields.
Ludlow told me that the atomic clock NIST is a scientific wall and door. It is a wall in the sense that it is so accurate that current geoid measurements actually limit the accuracy of the atomic clock since it provides geopotential resolution in the order of many centimeters while their clock can reduce the geopotential resolution to just a centimeter. On the other hand, the NIST clock is a gate in the sense can be used several times to improve the geodetic resolution. This would include the distribution of several such watches around the world and the measurement of slight deviations in the storage time to get the highest resolution of the map as Earth's gravity disperses space.
"If you had the watches that you believed were accurate at that very high level, you could use these watches as Earth's gravitational potential sensors, looking for changes in the beats speed when you moved to one hour through different parts of Earth's gravity," he told me is Ludlow.
Ludlow said that he and his NIST colleagues are currently working on prototypes for the portable version of their atomic clock that they can use to test this idea. It will probably be a few years before being distributed on Earth or in space, but in the meantime the NIST clock can be put for other purposes, such as redefining the second to even greater accuracy.