Last year, 2012, marked forty-five years since humanity decided to use atomic timekeeping to measure time as accurately as possible. In 1967, the International time category ceased to be determined by astronomical scales - they were replaced by the cesium frequency standard. It was he who received the now popular name - atomic clock. The exact time they allow to determine has an insignificant error of one second per three million years, which allows them to be used as a time standard in any corner of the world.
A little history
The very idea of using atomic vibrations for ultra-precise measurement of time was first expressed back in 1879 by British physicist William Thomson. This scientist proposed using hydrogen as an emitter of resonator atoms. The first attempts to put the idea into practice were made only in the 40s. twentieth century. The world's first working atomic clock appeared in 1955 in Great Britain. Their creator was the British experimental physicist Dr. Louis Essen. These clocks worked based on vibrations of cesium-133 atoms and thanks to them, scientists were finally able to measure time with much greater accuracy than before. Essen's first device allowed an error of no more than a second for every hundred years, but subsequently it increased many times and the error per second can accumulate only in 2-3 hundred million years.
Atomic clock: operating principle
How does this clever “device” work? Atomic clocks use molecules or atoms at the quantum level as a resonant frequency generator. establishes a connection between the “atomic nucleus - electrons” system and several discrete energy levels. If such a system is influenced with a strictly specified frequency, then a transition of this system from a low level to a high level will occur. The reverse process is also possible: the transition of an atom from a higher level to a lower one, accompanied by the emission of energy. These phenomena can be controlled and all energy jumps can be recorded by creating something like an oscillatory circuit (also called an atomic oscillator). Its resonant frequency will correspond to the energy difference between neighboring atomic transition levels, divided by Planck's constant.
Such an oscillatory circuit has undeniable advantages compared to its mechanical and astronomical predecessors. For one such atomic oscillator, the resonant frequency of the atoms of any substance will be the same, which cannot be said about pendulums and piezocrystals. In addition, atoms do not change their properties over time and do not wear out. Therefore, atomic clocks are extremely accurate and practically perpetual chronometers.
Accurate time and modern technologies
Telecommunication networks, satellite communications, GPS, NTP servers, electronic transactions on the stock exchange, Internet auctions, the procedure for purchasing tickets via the Internet - all these and many other phenomena have long been firmly established in our lives. But if humanity had not invented atomic clocks, all this simply would not have happened. Precise time, synchronization with which allows you to minimize any errors, delays and delays, allows a person to make the most of this invaluable irreplaceable resource, of which there is never too much.
We often hear the phrase that atomic clocks always show the exact time. But from their name it is difficult to understand why atomic clocks are the most accurate or how they work.
Just because the name contains the word “atomic” does not mean that the watch poses a danger to life, even if thoughts of an atomic bomb or a nuclear power plant immediately come to mind. In this case, we are just talking about the principle of operation of the watch. If in an ordinary mechanical watch the oscillatory movements are performed by gears and their movements are counted, then in an atomic clock the oscillations of electrons inside atoms are counted. To better understand the principle of operation, let's remember the physics of elementary particles.
All substances in our world are made of atoms. Atoms consist of protons, neutrons and electrons. Protons and neutrons combine with each other to form a nucleus, which is also called a nucleon. Electrons move around the nucleus, which can be at different energy levels. The most interesting thing is that when absorbing or releasing energy, an electron can move from its energy level to a higher or lower one. An electron can obtain energy from electromagnetic radiation, absorbing or emitting electromagnetic radiation of a certain frequency with each transition.
Most often, there are watches in which atoms of the element Cesium-133 are used for change. If in 1 second the pendulum regular watch makes 1 oscillatory motion, then the electrons in atomic clocks based on Cesium-133, when transitioning from one energy level to another, they emit electromagnetic radiation with a frequency of 9192631770 Hz. It turns out that one second is divided into exactly this number of intervals if it is calculated in atomic clocks. This value was officially adopted by the international community in 1967. Imagine a huge dial with not 60, but 9192631770 divisions, which make up only 1 second. It is not surprising that atomic clocks are so accurate and have a number of advantages: atoms are not subject to aging, do not wear out, and the oscillation frequency will always be the same for one chemical element, thanks to which it is possible to synchronously compare, for example, the readings of atomic clocks far in space and on Earth, without fear of errors.
Thanks to atomic clocks, humanity was able to test in practice the correctness of the theory of relativity and make sure that it is better than on Earth. Atomic clocks are installed on many satellites and spacecraft; they are used for telecommunications needs, for mobile communications, and they are used to compare the exact time on the entire planet. Without exaggeration, it was thanks to the invention of atomic clocks that humanity was able to enter the era of high technology.
How do atomic clocks work?
Cesium-133 is heated by evaporating cesium atoms, which are passed through a magnetic field, where atoms with the desired energy states are selected.
The selected atoms then pass through a magnetic field with a frequency close to 9192631770 Hz, which is created by a quartz oscillator. Under the influence of the field, cesium atoms again change energy states and fall on a detector, which records when the largest number of incoming atoms will have the “correct” energy state. The maximum number of atoms with a changed energy state indicates that the frequency of the microwave field is selected correctly, and then its value is fed into an electronic device - a frequency divider, which, reducing the frequency by an integer number of times, receives the number 1, which is the reference second.
Thus, cesium atoms are used to check the correct frequency of the magnetic field produced by the crystal oscillator, helping to maintain it at a constant value.
This is interesting: Although the current atomic clocks are unprecedentedly accurate and can run for millions of years without errors, physicists are not going to stop there. Using atoms of various chemical elements, they are constantly working to improve the accuracy of atomic clocks. Among the latest inventions is the atomic clock strontium, which are three times more accurate than their cesium counterpart. To lag behind just a second, they will need 15 billion years - time exceeding the age of our Universe...
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Isidor Rabi, a physics professor at Columbia University, has proposed a never-before-seen project: a clock operating on the principle of an atomic beam of magnetic resonance. This happened in 1945, and already in 1949 the National Bureau of Standards released the first working prototype. It read the vibrations of the ammonia molecule. Cesium came into use much later: the NBS-1 model appeared only in 1952.
The National Physical Laboratory in England created the first cesium beam clock in 1955. More than ten years later, during the General Conference on Weights and Measures, a more advanced clock was presented, also based on vibrations in the cesium atom. Model NBS-4 was used until 1990.
Types of watches
At the moment, there are three types of atomic clocks, which work on approximately the same principle. Cesium clocks, the most accurate, separate the cesium atom by a magnetic field. The simplest atomic clock, the rubidium clock, uses rubidium gas enclosed in a glass bulb. And finally, the hydrogen atomic clock takes as its reference point hydrogen atoms, closed in a shell of a special material - it prevents the atoms from quickly losing energy.
What time is it
In 1999, the US National Institute of Standards and Technology (NIST) proposed an even more advanced version of the atomic clock. The NIST-F1 model allows for an error of only one second every twenty million years.
The most accurate
But NIST physicists didn't stop there. Scientists decided to develop a new chronometer, this time based on strontium atoms. The new clock operates at 60% of the previous model, which means that it loses one second not in twenty million years, but in as many as five billion.
Measuring time
International agreement has determined the only precise frequency for the resonance of a cesium particle. This is 9,192,631,770 hertz - dividing the output signal by this number equals exactly one cycle per second.
Atomic clocks are the most accurate time measuring instruments that exist today, and are becoming increasingly important as modern technology develops and becomes more complex.
Operating principle
Atomic clocks keep accurate time not due to radioactive decay, as their name might suggest, but using vibrations of nuclei and the electrons surrounding them. Their frequency is determined by the mass of the nucleus, gravity and the electrostatic “balancer” between the positively charged nucleus and electrons. This does not quite correspond to a regular watch movement. Atomic clocks are more reliable time keepers because their oscillations do not change depending on environmental factors such as humidity, temperature or pressure.
Evolution of atomic clocks
Over the years, scientists have realized that atoms have resonant frequencies related to each's ability to absorb and emit electromagnetic radiation. In the 1930s and 1940s, high-frequency communications and radar equipment was developed that could interface with the resonance frequencies of atoms and molecules. This contributed to the idea of a watch.
The first examples were built in 1949 by the National Institute of Standards and Technology (NIST). Ammonia was used as a vibration source. However, they were not much more accurate than the existing time standard, and cesium was used in the next generation.
New standard
The change in precision of time measurement was so great that in 1967 the General Conference on Weights and Measures defined the SI second as 9,192,631,770 vibrations of a cesium atom at its resonant frequency. This meant that time was no longer related to the movement of the Earth. The world's most stable atomic clock was created in 1968 and was used as part of the NIST timekeeping system until the 1990s.
Improvement car
One of the latest advances in this area is laser cooling. This improved the signal-to-noise ratio and reduced the uncertainty in the clock signal. Housing this cooling system and other equipment used to improve cesium clocks would require space the size of a railroad car, although commercial versions could fit in a suitcase. One of these laboratory installations keeps time in Boulder, Colorado, and is the most accurate clock on Earth. They are only wrong by 2 nanoseconds per day, or 1 second per 1.4 million years.
Complex technology
This enormous precision is the result of a complex manufacturing process. First, liquid cesium is placed in a furnace and heated until it turns into a gas. The metal atoms exit at high speed through a small opening in the furnace. Electromagnets cause them to split into separate beams with different energies. The required beam passes through a U-shaped hole, and the atoms are irradiated with microwave energy with a frequency of 9,192,631,770 Hz. Thanks to this, they are excited and move into a different energy state. The magnetic field then filters out other energy states of the atoms.
The detector reacts to cesium and shows a maximum at the correct frequency value. This is necessary to configure the quartz oscillator that controls the clock mechanism. Dividing its frequency by 9.192.631.770 gives one pulse per second.
Not just cesium
Although the most common atomic clocks use the properties of cesium, there are other types. They differ in the element used and the means for determining changes in energy level. Other materials are hydrogen and rubidium. Hydrogen atomic clocks function similarly to cesium clocks, but require a container with walls made of a special material that prevents the atoms from losing energy too quickly. Rubidium watches are the simplest and most compact. In them, a glass cell filled with rubidium gas changes the absorption of light when exposed to ultrahigh frequency.
Who needs accurate time?
Today, time can be measured with extreme precision, but why is this important? This is necessary in systems such as mobile phones, the Internet, GPS, aviation programs and digital television. At first glance this is not obvious.
An example of how precise time is used is in packet synchronization. Thousands of telephone calls pass through the average communication line. This is only possible because the conversation is not transmitted completely. The telecommunications company splits it into small packets and even skips some of the information. They then pass through the line along with packets of other conversations and are restored at the other end without mixing. The telephone exchange's clocking system can determine which packets belong to a given conversation by the exact time the information was sent.
GPS
Another implementation of precise time is a global positioning system. It consists of 24 satellites that transmit their coordinates and time. Any GPS receiver can connect to them and compare broadcast times. The difference allows the user to determine their location. If these clocks were not very accurate, then the GPS system would be impractical and unreliable.
The limit of perfection
With the development of technology and atomic clocks, the inaccuracies of the Universe became noticeable. The earth moves unevenly, causing random variations in the length of years and days. In the past, these changes would have gone unnoticed because the tools for measuring time were too imprecise. However, much to the frustration of researchers and scientists, the time of atomic clocks has to be adjusted to compensate for real-world anomalies. They are amazing tools that help advance modern technology, but their excellence is limited by the limits set by nature itself.
An atomic clock is a device for very precise measurement of time. They got their name from the principle of their operation, since the natural vibrations of molecules or atoms are used as the period. Atomic clocks have found very wide application in navigation, in the space industry, for determining the location of satellites, in the military field, for detection, aircraft, and also in telecommunications.
There are apparently a lot of areas of application, but why do they all need such precision, since today the error of conventional atomic clocks is only 1 second in 30 million years? But there is something even more precise. Everything is understandable, because time is used to calculate distances, and there a small error can lead to hundreds of meters, or even kilometers, if we take cosmic distances. For example, let’s take the American GPS navigation system; when using a conventional electronic clock in the receiver, the error in measuring coordinates will be quite significant, which can affect all other calculations, and this can lead to consequences when it comes to space technologies. Naturally, for GPS receivers in mobile devices and other gadgets, greater accuracy is not at all important.
The most accurate time in Moscow and the world can be found on the official website - the “precise current time server” www.timeserver.ru
What are atomic clocks made of?
An atomic clock consists of several main parts: a quartz oscillator, a quantum discriminator and electronics units. The main one that sets the reference is a quartz oscillator, which is built on quartz crystals and produces, as a rule, a standard frequency of 10, 5, 2.5 MHz. Since the stable operation of quartz without error is quite small, it must be constantly adjusted.
The quantum discriminator records the frequency of the atomic line, and it is compared in the frequency-phase comparator with the frequency of the quartz oscillator. The comparator has feedback to the quartz oscillator to adjust it in case of frequency mismatch.
Atomic clocks cannot be built on all atoms. The most optimal is the cesium atom. It refers to the primary one against which all other suitable materials are compared, for example: strontium, rubidium, calcium. The primary standard is absolutely suitable for measuring precise time, which is why it is called primary.
The most accurate atomic clock in the world
To date most accurate atomic clock are located in the UK (officially adopted). Their error is only 1 second in 138 million years. They are the standard for the national time standards of many countries, including the United States, and also determine international atomic time. But the kingdom contains not the most accurate clocks on Earth.
most accurate atomic clock photo
The United States announced that it had developed an experimental type of precise clock based on cesium atoms; its error was 1 second in almost 1.5 billion years. Science in this area does not stand still and is developing at a rapid pace.
