Atomic clocks are the most accurate instruments for measuring time that exist today, and are becoming increasingly important with the development and sophistication of modern technologies.
Principle of operation
Atomic clocks are not precisely counted due to radioactive decay, as may seem by their name, but using oscillations of nuclei and surrounding electrons. 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 the usual clockwork. Atomic clocks are more reliable custodians of time, because their fluctuations do not change depending on environmental factors such as humidity, temperature or pressure.
The evolution of atomic clocks
For many years, scientists have realized that atoms have resonance frequencies associated with the ability of each to absorb and emit electromagnetic radiation. In the 1930s and 1940s, equipment was developed for high-frequency communications and radar, which could interact with the resonance frequencies of atoms and molecules. This contributed to the emergence of the idea of the watch.
The first copies were built in 1949 by the National Institute of Standards and Technology (NIST). As a source of vibration, ammonia was used in them. However, they were not much more accurate than the existing time standard, and in the next generation cesium was used.
The change in the accuracy of the time measurement turned out to be so great that in 1967 the General Conference on Measures and Weights determined the second SI as 9,192,631,770 vibrations of the cesium atom at its resonant frequency. This meant that time was no longer connected with the movement of the Earth. The most stable atomic clock in the world was created in 1968 and used as part of the NIST time reference system until the 1990s.
Car of improvements
One of the latest advances in this field is laser cooling. This improved the signal-to-noise ratio and reduced the uncertainty in the clock signal. To accommodate this cooling system and other equipment used to improve the cesium clock, it will take a place the size of a railway car, although commercial options can fit in a suitcase. One such laboratory facility counts down time in Boulder, Colorado, and is the most accurate clock on Earth. They are only 2 nanoseconds per day or 1.4 million years old.
Such great accuracy is the result of a complex technological process. First of all, the liquid cesium is placed in an oven and heated until it turns into a gas. Atoms of metal at high speed exit through a small hole in the furnace. Electromagnets force them to separate into separate beams with different energies. The required beam passes through a U-shaped hole, and the atoms are irradiated with a microwave energy of 9,192,631,770 Hz. Due to this they are excited and pass into another energy state. Then the magnetic field filters out other energy states of the atoms.
The detector reacts to cesium and shows a maximum with the correct frequency. This is necessary for tuning the crystal oscillator, which controls the timing mechanism. The division of its frequency into 9.192.631.770 and gives one pulse per second.
Not only cesium
Although the most common atomic clock uses the properties of cesium, there are other types of them. They differ in the element used and in the means for determining the change in the energy level. Other materials are hydrogen and rubidium. The atomic clock on hydrogen functions like cesium, but it requires a capacitance with walls of a special material, which prevents the atoms from losing energy too quickly. Rubidium watches are the most simple and compact. In them, a glass cell filled with gaseous rubidium changes the absorption of light when exposed to an ultrahigh frequency.
Who needs the exact time?
Today, time can be counted with special precision, but why is this important? This is necessary in such systems as mobile phones, the Internet, GPS, aviation programs and digital television. At first glance this is not obvious.
An example of how exact time is used is the synchronization of packets. Through the middle line of communication there are thousands of phone calls. This is possible only because the conversation is not transmitted completely. The telecommunications company divides it into small packages and even skips some of the information. Then they go through the line together with the packets of other conversations and on the other end they are restored without mixing. The clocking system of the telephone exchange can determine which packets belong to the given conversation, at the exact time of sending the information.
Another implementation of the exact time is the global positioning system. It consists of 24 satellites that transmit their coordinates and time. Any GPS receiver can connect to them and compare the broadcast time. The difference allows the user to determine their location. If this clock were not very accurate, then the GPS system would be impractical and unreliable.
The Limit of Excellence
With the development of technology and atomic clocks, the inaccuracies of the universe have become noticeable. The earth moves unevenly, which leads to random fluctuations in the duration of years and days. In the past, these changes would have remained unnoticed, since time-measuring tools were too inaccurate. However, to the great disappointment of researchers and scientists, the time of atomic clocks has to be adjusted to compensate for real-world anomalies. They are amazing tools that promote the advancement of modern technologies, but their perfection is limited by the limits established by nature itself.