Atomic clocks are the most accurate time measurement devices that exist today and are becoming increasingly important with the development and sophistication of modern technologies.
Principle of operation
Atomic clocks do not count the exact time due to radioactive decay, as their name suggests, but using vibrations of the nuclei and the electrons surrounding them. Their frequency is determined by the mass of the nucleus, gravity and electrostatic "balance" between the positively charged nucleus and electrons. This is not entirely consistent with the usual clockwork. Atomic clocks are more reliable time keepers, because their fluctuations do not change depending on environmental factors such as humidity, temperature, or pressure.
Atomic clock evolution
For many years, scientists realized that atoms have resonant frequencies associated with the ability of each to absorb and emit electromagnetic radiation. In the 1930s and 1940s, equipment for high-frequency communications and radars was developed, which could interact with the resonance frequencies of atoms and molecules. This contributed to the idea of watches.
The first copies were built in 1949 by the National Institute of Standards and Technology (NIST). Ammonia was used as a source of vibration. However, they were not much more accurate than the existing standard of time, and cesium was used in the next generation.
The change in the accuracy of time measurement turned out to be so large that in 1967 the General Conference on Measures and Weights defined the second SI as 9,192,631,770 oscillations of a cesium atom at its resonant frequency. This meant that time was no longer associated with the motion of the Earth. The most stable atomic clocks in the world were created in 1968 and were used as part of the NIST time reference system until the 1990s.
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. To accommodate this cooling system and other equipment used to improve cesium clocks, space is required the size of a railway car, although commercial options can fit in a suitcase. One such laboratory setup counts time in Boulder, Colorado, and is the most accurate clock on Earth. They are mistaken only for 2 nanoseconds per day or for 1 s in 1.4 million years.
Such enormous accuracy is the result of a complex process. First of all, liquid cesium is placed in a furnace and heated until it turns into gas. Metal atoms at high speed exit through a small hole in the furnace. Electromagnets make them split into separate beams with different energies. The required beam passes through a U-shaped hole, and the atoms are exposed to microwave energy at a frequency of 9.192.631.770 Hz. Due to this, they are excited and move to another energy state. Then the magnetic field filters out other atomic energy states.
The detector responds to cesium and shows a maximum at the correct frequency. This is necessary to configure the crystal oscillator that controls the clocking mechanism. Dividing its frequency by 9.192.631.770 and gives one pulse per second.
Not only cesium
Although the most common atomic clocks use the properties of cesium, there are other types of them. They differ in the element used and the means for determining changes in the energy level. Other materials are hydrogen and rubidium. Atomic clocks on hydrogen function like cesium, but they require a container with walls made of a special material that prevents the atoms from losing energy too quickly. Rubidium clocks are the most simple and compact. In them, a glass cell filled with rubidium gas changes the absorption of light when exposed to ultra high frequency.
Who needs exact time?
Today, time can be counted 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 exact time is used is packet synchronization. Thousands of phone calls go through the middle line. This is only possible because the conversation is not transmitted completely. The telecommunications company divides it into small packets and even skips some of the information. Then they go through the line along with the packets of other conversations and at the other end are restored without being mixed. The clocking system of the telephone exchange can determine which packets belong to this conversation, according to 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 with them and compare broadcast times. The difference allows the user to determine their location. If this watch were not very accurate, then the GPS system would be impractical and unreliable.
With the development of technology and atomic clocks, inaccuracies of the Universe have become noticeable. The earth moves unevenly, which leads to random variations in the duration of years and days. In the past, these changes would go unnoticed, because the tools for measuring time were too imprecise. However, to the great disappointment of researchers and scientists, the time of the atomic clock has to be adjusted to compensate for the anomalies of the real world. They are amazing tools that contribute to the advancement of modern technology, but their perfection is limited by the limits set by nature itself.