Almost as tall as a man and weighing more than 350 kilograms, it did not look like a clock in the usual sense. It had no dial or hands, but cabinets with electronics, a vacuum system, and an apparatus in which cesium atoms set the rhythm. This was the Atomichron – the first commercial atomic clock.
The historical date is October 3, 1956, not October 2, as some anniversary calendars indicate. The Smithsonian archives and a historical study published in the journal of the Institute of Electrical and Electronics Engineers indicate that the device was unveiled at the Overseas Press Club in New York on October 3. The discrepancy probably comes from the different counting of the day on which the clock was exhibited or put into operation.
Clock without a pendulum
The Atomichron was developed by the National Company with the participation of physicist Jerrold Zacharias of the Massachusetts Institute of Technology, as well as Richard Daly and other engineers. Instead of a pendulum, a quartz crystal or the rotation of the Earth, the device uses the natural frequency of cesium atoms.
A stream of cesium atoms is created inside the device, which passes through a microwave field. When the frequency is set correctly, the atoms change their energy state. Electronics register this transition and keep the signal stable. Thus, the atom becomes a kind of pendulum, but with billions of oscillations per second.
The price of the device is about $ 50,000 – an amount that would exceed $500,000 today. The first units were intended mainly for military laboratories and scientific centers. For the needs of communications, navigation and radar systems, an accurate frequency standard is no longer a luxury, but a strategic necessity.
“It performs far beyond expectations“ – is how the US Army Signal Corps assessed the performance of the Atomichron, according to the Smithsonian.Before and after Atomichron
The presentation in New York was not the beginning of atomic timekeeping. The first atomic clock was created in 1949 by scientists at the US National Bureau of Standards, now the National Institute of Standards and Technology. It used ammonia, but it was not sufficiently superior to existing electronic clocks.
A more important breakthrough came in 1955, when Louis Essen and Jack Parry at the UK's National Physical Laboratory created the first cesium clock stable enough to serve as a frequency standard. A year later, the Atomichron showed that the technology could leave the laboratory and become a commercial product.
Today, a second is defined by exactly 9,192,631,770 periods of the radiation in the transition between two energy levels of the cesium-133 atom. This definition was adopted in 1967 and is behind the operation of global navigation systems, telecommunications and synchronized computer networks.
So the story of the Atomichron is not just the story of an unusual, heavy device from the 1950s. This is the moment when humanity began to measure time not by the movement of celestial bodies or mechanical parts, but by the constant rhythm of the atoms themselves.