In the past, 2012, forty-five years have passed since the moment when humanity decided to use atomic timekeeping to measure time as accurately as possible. In 1967, the International category of time was no longer defined 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 that they allow to determine has a negligible error of one second in three million years, which allows them to be used as a time standard in any corner of the world.
A bit of history
The very idea of using the vibrations of atoms for ultra-precise measurement of time was first proposed back in 1879 by the British physicist William Thomson. In the role of the emitter of atoms-resonators, this scientist proposed to use hydrogen. The first attempts to put the idea into practice were made only in the 40s. twentieth century. And the world's first working atomic clock appeared in 1955 in Great Britain. They were created by the British experimental physicist Dr. Louis Essen. This clock worked on the basis of vibrations of atoms of cesium-133, and thanks to them, scientists were finally able to measure time with much greater accuracy than before. Essen's first instrument 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 only run over 2-3 hundreds of millions of years.
Atomic clock: how it works
How does this clever "device" work? As a resonant frequency generator, atomic clocks use molecules or atoms at the quantum level. establishes system connection " atomic nucleus- electrons "with several discrete energy levels. If such a system is acted upon with a strictly specified frequency, then this system will transition from low level on high. The reverse process is also possible: the transition of an atom from more high level to low, accompanied by the emission of energy. These phenomena can be controlled and recorded all energy jumps, creating something like an oscillatory circuit (it is also called an atomic oscillator). Its resonant frequency will correspond to the energy difference between neighboring transition levels of atoms, divided by the Planck constant.
Such an oscillatory circuit has undeniable advantages in comparison with 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 piezo crystals. In addition, atoms do not change their properties over time and do not wear out. Therefore, the atomic clock is an extremely accurate and almost perpetual chronometer.
Precise time and modern technology
Telecommunication networks, satellite communications, GPS, NTP servers, electronic transactions on the stock exchange, Internet auctions, the procedure for buying tickets via the Internet - all these and many other phenomena have long been firmly entrenched in our life. But if humanity had not invented the atomic clock, all this would simply not have happened. The exact time, synchronization with which allows you to minimize any errors, delays and delays, enables a person to make the most of this invaluable irreplaceable resource, of which there is never too much.
, Galileo) are impossible without an atomic clock. Atomic clocks are also used in satellite and terrestrial telecommunication systems, including base stations mobile communications, international and national bureaus of standards and precision time services, which periodically broadcast temporary signals on the radio.
Clock device
The watch consists of several parts:
- quantum discriminator,
- complex of electronics.
National Frequency Standards Centers
Many countries have formed national centers for time and frequency standards:
- (VNIIFTRI), item Mendeleevo, Moscow region;
- (NIST), Boulder (USA, Colorado);
- National Institute of Advanced Industrial Science and Technology () (AIST), Tokyo (Japan);
- Federal Physical and Technical Agency (German)(PTB), Braunschweig (Germany);
- National Laboratory for Metrology and Testing (fr.)(LNE), Paris (France).
- UK National Physics Laboratory (NPL), London, UK.
Scientists different countries work to improve atomic clocks and state primary standards of time and frequency based on them, the accuracy of such clocks is steadily increasing. In Russia, extensive research aimed at improving the characteristics of atomic clocks is carried out in.
Types of atomic clocks
Not every atom (molecule) is suitable as a discriminator for an atomic clock. Choose atoms that are insensitive to various external influences: magnetic, electric and electromagnetic fields... There are such atoms in every range of the electromagnetic radiation spectrum. These are: atoms of calcium, rubidium, cesium, strontium, molecules of hydrogen, iodine, methane, osmium (VIII) oxide, etc. The hyperfine transition of the cesium atom was chosen as the main (primary) frequency standard. The characteristics of all other (secondary) standards are compared with this standard. In order to carry out such a comparison, so-called optical combs are currently used. (English)- radiation with a wide frequency spectrum in the form of equidistant lines, the distance between which is referenced to the atomic frequency standard. The optical combs are produced using a mode-locked femtosecond laser and microstructured fiber, in which the spectrum is broadened to one octave.
In 2006, researchers at the US National Institute of Standards and Technology, led by Jim Bergquist, developed a clock that operates on a single atom. During the transitions between the energy levels of the mercury ion, photons of the visible range are generated with a stability 5 times higher than the microwave radiation of cesium-133. The new watch can also find application in studies of the dependence of changes in fundamental physical constants on time. As of April 2015, the most accurate atomic clock is one created by the US National Institute of Standards and Technology. The error was only one second in 15 billion years. As one of possible applications hours indicated relativistic geodesy, the main idea of which is to use a network of clocks as gravitational sensors, which will help to carry out an incredibly detailed three-dimensional measurement of the shape of the Earth.
Active development of compact atomic clocks for use in Everyday life (wrist watch, mobile devices) . Early 2011 American company Symmetricom announced the commercial release of a cesium atomic clock the size of a small microcircuit. The clock works on the basis of the effect of coherent population trapping. Their stability is 5 · 10 -11 per hour, weight - 35 g, power consumption - 115 mW.
Notes (edit)
- A new record for the accuracy of atomic clocks has been set (unspecified) ... Membrana. 5 February 2010. Retrieved March 4, 2011. Archived February 9, 2012.
- The indicated frequencies are characteristic precisely for precision quartz resonators, with the highest quality factor and frequency stability attainable when using the piezoelectric effect. In general, crystal oscillators are used at frequencies from a few kHz to several hundred MHz. ( Altshuller G.B., Elfimov N.N., Shakulin V.G. Quartz Oscillators: A Reference Guide. - M.: Radio and communication, 1984 .-- S. 121, 122 .-- 232 p. - 27,000 copies.)
- N. G. Basov, V. S. Letokhov. Optical frequency standards. // Phys. - 1968. - T. 96, No. 12.
- National metrology laboratories. NIST, February 3, 2011. (Retrieved June 14, 2011)
- Oskay W., Diddams S., Donley A., Frotier T., Heavner T., et al. Single-Atom Optical Clock with High Accuracy // Phys. Rev. Lett. ... - American Physical Society, July 4, 2006. - Vol. 97, no. 2. -
A sensation swept the scientific world - from our Universe ... time evaporates! So far, this is only a hypothesis of Spanish astrophysicists. But the fact that the flow of time on Earth and in space is different has already been proven by scientists. Time under the influence of gravity flows more slowly, accelerating with distance from the planet. The task of synchronizing the terrestrial and cosmic time is performed by hydrogen frequency standards, which are also called "atomic clocks".
The first atomic time appeared along with the emergence of astronautics; atomic clocks appeared in the mid-1920s. Now atomic clocks have become an everyday thing, each of us uses them every day: with their help, digital communications, GLONASS, navigation, and transport work.
Mobile phone owners hardly think about which hard work in space, it is carried out for strict time synchronization, but we are talking only about millionths of a second.
The standard of exact time is kept in the Moscow region, in Scientific Institute physical-technical and radio-technical measurements. There are 450 such watches in the world.
Russia and the United States are monopolists for atomic clocks, but in the United States, clocks are based on cesium, a radioactive metal that is very harmful to the environment, and in Russia, on the basis of hydrogen, a safer durable material.
This watch has no dial and hands: it looks like a large barrel made of rare and precious metals, filled with the most advanced technologies - high-precision measuring instruments and equipment with atomic standards. The process of their creation is very long, complex and takes place under conditions of absolute sterility.
For 4 years now, the clock installed on the Russian satellite has been studying dark energy... By human standards, they lose accuracy by 1 second over many millions of years.
Very soon, an atomic clock will be installed on Spektr-M - a space observatory that will see how stars and exoplanets are formed, look over the edge black hole in the center of our Galaxy. According to scientists, due to the monstrous gravity, time flows here so slowly that it almost stops.
tvroscosmos
A new impetus in the development of devices for measuring time was given by atomic physicists.
In 1949, the first atomic clock was built, where the source of oscillations was not a pendulum or a quartz generator, but signals associated with quantum transition electron between two energy levels of an atom.
In practice, such clocks turned out to be not very accurate, moreover, they were cumbersome and expensive and did not become widespread. Then it was decided to contact chemical element- cesium. And in 1955, the first atomic clock based on cesium atoms appeared.
In 1967, it was decided to switch to an atomic time standard, since the Earth's rotation slows down and the magnitude of this slowdown is not constant. This made the work of astronomers and keepers of Time much more difficult.
The Earth is currently rotating at a deceleration rate of about 2 milliseconds over 100 years.
Fluctuations in the length of the day also reach thousandths of a second. Therefore, the accuracy of the Greenwich Mean Time (the generally accepted world standard since 1884) became insufficient. In 1967, the transition to the atomic standard of time took place.
Today, a second is a period of time exactly equal to 9 192 631 770 periods of radiation, which corresponds to the transition between two hyperfine levels of the ground state of the atom of Cesium 133.
At the moment, Coordinated Universal Time is used as a time scale. It is formed by the International Bureau of Weights and Measures by combining data from time keeping laboratories from different countries, as well as data from the International Earth Rotation Service. It is nearly a million times more accurate than astronomical Greenwich Mean Time.
A technology has been developed that will make it possible to radically reduce the size and cost of ultra-precise atomic clocks, which will make it possible to widely use them in mobile devices most for various purposes... Scientists were able to create an ultra-small atomic time standard. Such atomic clocks consume less than 0.075 W and have an error of no more than one second in 300 years.
Research group The USA managed to create an ultra-compact atomic standard. It became possible to power atomic clocks from conventional AA batteries. Ultra-precise atomic clocks, usually at least a meter in height, were placed in a volume of 1.5x1.5x4 mm
An experimental atomic clock based on one mercury ion has been developed in the USA. They are five times more accurate than cesium, which are accepted as an international standard. Cesium clocks are so accurate that a discrepancy of one second will be achieved only after 70 million years, while for mercury clocks this period will be 400 million years.
In 1982, a new astronomical object - a millisecond pulsar - intervened in the dispute between the astronomical definition of the standard of Time and the atomic clock that won it. These signals are as stable as the best atomic clocks.
Did you know?
The first hours in Russia
In 1412, a clock was set in Moscow in the courtyard of the Grand Duke behind the Church of the Annunciation, and it was made by Lazar, a Serb monk who came from the Serbian land. Unfortunately, descriptions of these first clocks in Russia have not survived.
________How did the chimes appear on the Spasskaya Tower of the Moscow Kremlin?
In the 17th century, the Englishman Christopher Galovey made chimes for the Spasskaya Tower: the hour circle was divided into 17 sectors, the only hand of the clock was motionless, directed downward and pointed to any number on the dial, but the dial itself rotated.
Atomic clocks are the most accurate time measuring instruments that exist today and are purchased by all greater importance with development and complication modern technologies.
Principle of operation
Atomic clocks do not count down the exact time due to radioactive decay, as their name may seem, but using the vibrations of nuclei and the electrons surrounding them. Their frequency is determined by the mass of the nucleus, gravity and the electrostatic "balance" between the positively charged nucleus and electrons. This is not entirely consistent with a conventional watch movement. Atomic clocks are more reliable timekeepers because their fluctuations do not change depending on such factors. environment like humidity, temperature or pressure.
Evolution of the atomic clock
Over the years, scientists have realized that atoms have resonant frequencies associated with everyone's ability to absorb and emit electromagnetic radiation... In the 1930s and 1940s, high-frequency communications and radar equipment was developed that could interact with the resonance frequencies of atoms and molecules. This contributed to the emergence of the idea of watches.
The first examples were built in 1949. The National Institute standards and technologies (NIST). They used ammonia as a vibration source. However, they turned out to be not much more accurate than the existing time standard, and cesium was used in the next generation.
The new standard
The change in the accuracy of time measurement turned out to be so great that in 1967 the General Conference on Weights and Measures determined the SI second as 9 192 631 770 vibrations of the cesium atom at its resonant frequency. This meant that time was no longer associated with the movement of the Earth. The world's most stable atomic clock was created in 1968 and was used as part of the NIST time frame until the 1990s.
Improvement wagon
One of recent advances in this area is laser cooling. This improved the signal-to-noise ratio and reduced clock uncertainty. This cooling system and other equipment used to improve the cesium clocks will require space the size of a railroad car, although commercial options can fit in a suitcase. One of these laboratory installations counts the time in Boulder, Colorado, and is the most accurate clock on Earth. They are only wrong by 2 nanoseconds per day, or 1 s every 1.4 million years.
Complex technology
Such tremendous precision is the result of a complex technological process... First of all, liquid cesium is placed in an oven and heated until it turns into a gas. The metal atoms are ejected at high speed through a small hole in the furnace. Electromagnets cause them to split into separate beams of different energies. The required beam passes through the U-shaped hole and the atoms are irradiated with microwave energy at a frequency of 9.192.631.770 Hz. Due to this, they are excited and pass into another energy state. The magnetic field then filters out other energy states of the atoms.
The detector reacts to cesium and shows a maximum at correct meaning frequency. This is required to configure crystal oscillator that controls the timing mechanism. Dividing its frequency by 9.192.631.770 gives one pulse per second.
Not only cesium
Although the most common atomic clocks use the properties of cesium, there are other types. They differ in the element used and in the means of determining the change in the energy level. Other materials are hydrogen and rubidium. An atomic clock on hydrogen functions like a cesium one, but requires 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 ones. In them, a glass cell filled with gaseous rubidium changes the absorption of light when exposed to ultra-high frequency.
Who needs accurate time?
Today, time can be counted with great precision, but why is it important? This is necessary in systems such as mobile phones, internet, GPS, aviation programs and digital television... At first glance, this is not obvious.
An example of how accurate time is used is packet synchronization. Thousands of phone calls go through the middle line. This is only possible because the conversation is not fully transmitted. The telecommunications company divides it into small packages and even skips some information. They then travel through the line along with packets of other conversations, and are reconstituted at the other end without mixing. The telephone exchange clock system can determine which packets belong to a given conversation by the exact time of sending the information.
Gps
Another implementation of accurate time is the global positioning system. It consists of 24 satellites that transmit their coordinates and time. Any GPS receiver can connect with them and compare broadcast times. The difference allows the user to determine their location. If this clock were not very accurate, 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 have become noticeable. The earth moves unevenly, resulting in random fluctuations in the length of the years and days. In the past, these changes would have gone unnoticed because the instruments for measuring time were too imprecise. However, much to the dismay of researchers and scientists, the time of the atomic clock has to be adjusted to compensate for the anomalies. the real world... They are amazing tools to help advance modern technology, but their perfection is limited by the limits set by nature itself.
