Arrows of time: how atomic clocks work. Atomic clock: a device for measuring the time of satellite and navigation systems

These are devices for measuring time, the operating principle of which is based on atomic physics. Due to the properties of the chemical elements used in the design, the error of these watches is minimal. For example, devices based on thorium-229 will lag by a tenth of a second in about 14 billion years.

How do atomic clocks work?

If in quartz watch The reference frequency for determining the second is the number of vibrations of a quartz crystal, then in atomic ones it is taken to be the frequency of transitions of electrons in the atoms of certain chemical elements from one energy level to another.

1 - Electronic component (chip)

2 - Nuclear source

3 - Photodetector

4 - Upper heater

5 - Resonant cell

6 - Wave plate

7 - Bottom heater

8 - Vertical emitting laser

Here's the point: atoms have electrons. They have energy. When absorbing or releasing energy, electrons jump from one energy level to another, absorbing or emitting electromagnetic waves, the frequency of which is always the same. This phenomenon can be controlled: when an atom is exposed to microwave radiation, it responds with a certain number of vibrations.

This property is used to improve the accuracy of time measurements. Thus, it is recognized that a second is the duration of 9192631770 radiation cycles. This frequency corresponds to the transition between two energy levels of the cesium-133 atom. By comparing the oscillation frequency of a quartz oscillator with the transition frequency of the element’s atoms, the slightest deviations are recorded. If there are deviations, the quartz vibrations are adjusted.

Cesium is not the only material used in atomic clocks. Devices based on chemical elements are appearing that can provide even greater precision: ytterbium, thorium-229, strontium.

Why are atomic clocks accurate?

The vibration frequency of the chemical element is the same, and this minimizes the possibility of error. In addition, unlike a quartz crystal, the atoms do not wear out or lose their Chemical properties with time.

Other names for atomic clocks: quantum, molecular.

Atomic clock are the most accurate time measuring instruments that exist today, and are becoming increasingly popular higher value with development and complexity modern technologies.

Principle of operation

Atomic clocks keep accurate time not thanks 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 such factors environment, 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 the 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 complex technological 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 correct value frequencies. 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 Cell phones, 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 anomalies real world. They are amazing tools that help advance modern technology, but their excellence is limited by the limits set by nature itself.

Time, despite the fact that scientists still cannot finally unravel its true essence, still has its own units of measurement established by humanity. And a calculation device called a clock. What are their varieties, what are the most accurate watch in the world? This will be discussed in our material today.

What is the most accurate watch in the world?

They are considered to be atomic - they have minute errors that can reach only seconds per billion years. The 2nd, no less honorable, podium is won. They lag behind for a month or rush forward by only 10-15 seconds. But mechanical watches are not the most accurate in the world. They need to be started and started up all the time, and here the errors are of a completely different order.

The most accurate atomic clock in the world

As has already been said, atomic instruments for qualitative measurement of time are so meticulous that the errors they give can be compared with measurements of the diameter of our planet down to every microparticle. Undoubtedly, the average person in everyday life does not need such precise mechanisms at all. These are used by scientific researchers to conduct various experiments where extreme calculations are required. They provide opportunities for people to check “time progress” in various areas globe or conduct experiments that confirm general theory relativity, as well as others physical theories and hypotheses.

Paris standard

What is the most accurate watch in the world? It is generally accepted that they are Parisian, belonging to the Institute of Time. This device is the so-called time standard; people all over the world check it against it. By the way, in fact, it is not quite similar to “walkers” in the traditional sense of the word, but resembles a very precise device of the most complex design, which is based on the quantum principle, and main idea- calculation of space-time using particle vibrations with errors equal to only 1 second per 1000 years.

Even more precise

What is the most accurate watch in the world today? In current realities, scientists have invented a device that is 100 thousand times more accurate than the Paris standard. Its error is one second in 3.7 billion years! A group of physicists from the USA is responsible for the development of this technology. It is already the second version of time devices built on quantum logic, where information processing is carried out using a method similar to, for example,

Research assistance

The latest quantum devices not only set new standards in the measurement of such quantities as time, but also help researchers in many countries resolve some questions that are associated with such physical constants as speed light beam in a vacuum or Planck's constant. The increasing precision of measurements is beneficial for scientists, who hope to track the time dilation caused by gravity. And one technology company in the United States plans to launch even mass-produced quantum watches for everyday use. True, how high will their primary cost be?

Operating principle

Atomic clocks are also commonly called quantum clocks, because they operate on the basis of processes that occur at the molecular level. To create high-precision devices, not just any atoms are taken: usually the use of calcium and iodine, cesium and rubidium, and also hydrogen molecules is typical. On this moment The most accurate mechanisms for calculating time based on ittiberium were produced by the Americans. Over 10 thousand atoms are involved in the operation of the equipment, which ensures excellent accuracy. By the way, the previous record holders had an error per second of “only” 100 million, which, you see, is also a considerable period.

Precision quartz...

When choosing household “walkers” for everyday use, of course, nuclear devices should not be taken into account. Among household watches today, the most accurate watches in the world are quartz ones, which also have a number of advantages over mechanical ones: they do not require winding and work using crystals. Their running errors average 15 seconds per month (mechanical ones can usually lag by this amount of time per day). And the most accurate wrist watch Of all the quartz watches in the world, according to many experts, the Citizen company is Chronomaster. They can have an error of only 5 seconds per year. In terms of cost, they are quite expensive - around 4 thousand euros. On the second step of the imaginary Longines podium (10 seconds per year). They are already much cheaper - about 1000 euros.

...and mechanical

Most mechanical instruments, as a rule, are not particularly accurate. However, one of the devices can still boast. The watch, made in the 20th century, has a huge mechanism of 14 thousand elements. Thanks to complex design, as well as the rather slow functionality of their measurement errors - a second for every 600 years.

When the light suddenly goes out and comes back a little later, how do you know what time to set the clock? Yes, I'm talking about Digital Watch, which many of us probably have. Have you ever thought about how time is regulated? In this article, we will learn all about the atomic clock and how it makes the whole world tick.

Are atomic clocks radioactive?

Atomic clocks tell time better than any other clock. They show time better than the rotation of the Earth and the movement of the stars. Without atomic clocks, GPS navigation would be impossible, the Internet would not be synchronized, and the positions of the planets would not be known with sufficient accuracy for space probes and vehicles.

Atomic clocks are not radioactive. They do not rely on atomic fission. Moreover, it has a spring, just like a regular watch. The biggest difference between a standard clock and an atomic clock is that oscillations in an atomic clock occur in the nucleus of an atom between the electrons surrounding it. These oscillations are hardly parallel to the balance wheel on a winding watch, but both types of oscillation can be used to track the passage of time. The frequency of vibrations within an atom is determined by the mass of the nucleus, gravity, and the electrostatic “spring” between the positive charge of the nucleus and the cloud of electrons around it.

What types of atomic clocks do we know?

Today there are Various types atomic clocks, but they are built on the same principles. The main difference relates to the element and means of detecting changes in energy levels. Among different types There are the following atomic clocks:

• Cesium atomic clocks using beams of cesium atoms. The clock separates cesium atoms with different energy levels using a magnetic field.
• A hydrogen atomic clock maintains hydrogen atoms at the desired energy level in a container whose walls are made of special material, so the atoms don't lose their high-energy state too quickly.
• Rubidium atomic clocks, the simplest and most compact of all, use a glass cell containing rubidium gas.

The most accurate atomic clocks today use a cesium atom and a conventional magnetic field with detectors. In addition, the cesium atoms are contained by the laser beams, which reduces small changes in frequency due to the Doppler effect.

How do cesium-based atomic clocks work?

Atoms have a characteristic vibration frequency. A familiar example of frequency is the orange glow of sodium in table salt if thrown into the fire. An atom has many different frequencies, some in the radio range, some in the visible spectrum, and some in between. Cesium-133 is most often chosen for atomic clocks.

To cause the cesium atoms to resonate in an atomic clock, one of the transitions, or the resonant frequency, must be accurately measured. This is usually done by locking a crystal oscillator into the fundamental microwave resonance of the cesium atom. This signal is in the microwave range of the radio frequency spectrum and has the same frequency as direct broadcast satellite signals. Engineers know how to create equipment for this spectrum region, in great detail.

To create a clock, cesium is first heated so that the atoms are vaporized and passed through a high-vacuum tube. They first pass through a magnetic field, which selects atoms with the desired energy state; they then pass through an intense microwave field. The frequency of microwave energy jumps back and forth in a narrow range of frequencies so that at a certain point it reaches a frequency of 9,192,631,770 hertz (Hz, or cycles per second). The range of the microwave oscillator is already close to this frequency because it is produced by a precise crystal oscillator. When a cesium atom receives microwave energy of the desired frequency, it changes its energy state.

At the end of the tube, another magnetic field separates atoms that have changed their energy state if the microwave field was of the right frequency. The detector at the end of the tube produces an output signal proportional to the number of cesium atoms that hit it, and peaks when the microwave frequency is sufficiently correct. This peak signal is needed for correction to bring the crystal oscillator, and therefore the microwave field, to the desired frequency. This blocked frequency is then divided by 9,192,631,770 to give the familiar one pulse per second that the real world needs.

When was the atomic clock invented?

In 1945, Columbia University physics professor Isidor Rabi proposed a clock that could be made based on techniques developed in the 1930s. It was called atomic beam magnetic resonance. By 1949, the National Bureau of Standards announced the creation of the world's first atomic clock based on the ammonia molecule, the vibrations of which were read, and by 1952 it created the world's first atomic clock based on cesium atoms, NBS-1.

In 1955, the National Physical Laboratory in England built the first clock using a cesium beam as a calibration source. Over the next decade, more advanced watches were created. In 1967, during the 13th General Conference on Weights and Measures, the SI second was determined based on vibrations in the cesium atom. There was no timekeeping system in the world more precise definitions than this. NBS-4, the world's most stable cesium clock, was completed in 1968 and was in use until 1990.

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 oscillator, but signals associated with the quantum transition of an electron between two energy levels of an atom.

In practice, such clocks turned out to be not very accurate, moreover, they were bulky and expensive and were not widely used. Then it was decided to contact chemical element- cesium. And in 1955, the first atomic clocks based on cesium atoms appeared.

In 1967, it was decided to switch to the atomic time standard, since the rotation of the Earth is slowing down and the magnitude of this slowdown is not constant. This made the work of astronomers and time keepers much more difficult.

The Earth currently rotates at a rate of about 2 milliseconds per 100 years.

Fluctuations in the length of the day also reach thousandths of a second. Therefore, the accuracy of Greenwich Mean Time (generally accepted as a global standard since 1884) has become insufficient. In 1967, the transition to the atomic time standard 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 Cesium 133 atom.

Currently, Coordinated Universal Time is used as the time scale. It is formed by the International Bureau of Weights and Measures by combining data from time storage laboratories various countries, as well as data from the International Earth Rotation Service. Its accuracy is almost a million times higher than astronomical Greenwich Mean Time.

A technology has been developed that will radically reduce the size and cost of ultra-precise atomic clocks, which will make it possible to widely use them in mobile devices himself for various purposes. Scientists were able to create an atomic time standard of ultra-small size. Such atomic clocks consume less than 0.075 W and have an error of no more than one second in 300 years.

A US research group has succeeded in creating an ultra-compact atomic standard. It has become possible to power atomic clocks from ordinary AA batteries. Ultra-precise atomic clocks, usually at least a meter high, were placed in a volume of 1.5x1.5x4 mm

An experimental atomic clock based on a single mercury ion has been developed in the USA. They are five times more accurate than cesium, which is accepted as the international standard. Cesium clocks are so accurate that it will take 70 million years for a discrepancy of one second to be achieved, 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 Time standard and the atomic clock that won it. These signals are as stable as the best atomic clocks

Did you know?

The first clocks in Rus'

In 1412 in Moscow, a clock was placed in the courtyard of the Grand Duke behind the Church of the Annunciation, and it was made by Lazar, a Serbian monk who came from the Serbian land. Unfortunately, no description of these first clocks in Rus' has been preserved.

How did the chiming clock appear on the Spasskaya Tower of the Moscow Kremlin?

In the 17th century, the Englishman Christopher Galloway made chimes for the Spasskaya Tower: the hour circle was divided into 17 sectors, the only clock hand was stationary, directed downwards and pointed at some number on the dial, but the dial itself rotated.