Who decides how long a second is? - John Kitching

Summary

The script explores the quest to define a second scientifically. From ancient calendars to the Gregorian system, timekeeping evolved with society's needs. By the 1950s, atomic clocks emerged, using cesium-133 atoms' consistent oscillations for precision. In 1967, the International Committee standardized a second as 9,192,631,770 cesium atom ticks, leading to globally synchronized atomic clocks that enhance our daily lives and technology.

Takeaways

• 🕒 The script discusses the scientific quest to define a second, a fundamental unit of time, with precision.
• 🌌 Ancient civilizations used calendars to measure time, but the second was not a defined unit until the Gregorian calendar's introduction in the late 1500s.
• 📅 The Gregorian calendar defined a day as a single Earth revolution, dividing it into 24 hours, 60 minutes, and 60 seconds.
• 🔬 The second was initially a mathematical concept, becoming crucial for precise timekeeping with the rise of interconnected societies and fast-moving transportation.
• 🚂 The need for exact timekeeping arose with the advent of railways, requiring cities to synchronize their clocks.
• ⚛️ By the 1950s, atomic clocks were developed, using the consistent frequency of electron oscillations in atoms as a basis for time measurement.
• 🌐 Atomic clocks rely on the laws of quantum mechanics and the unchanging physical properties of atoms for accurate timekeeping.
• 🌌 The cesium-133 atom was chosen as the standard for timekeeping due to its long-lived, high-frequency electron oscillations and simple energy level structure.
• 🏆 In 1967, the Thirteenth General Conference of the International Committee for Weights and Measures decided on cesium-133 as the basis for the second.
• 🔢 One second was officially defined as 9,192,631,770 ticks of a cesium-133 atom, based on the most precise astronomical measurements available.
• 🌍 Today, atomic clocks are utilized globally for synchronization in various applications, including radio signal transmitters and global positioning systems.

Q & A

What was the main scientific question researchers attempted to answer in 1967?

The main scientific question was to determine the precise length of a second.

How was time measured by ancient civilizations?

Ancient civilizations measured time with unique calendars that tracked the steady march of the night sky.

When was the concept of a second as we know it first introduced?

The concept of a second as we know it was first introduced in the late 1500s with the Gregorian calendar.

Why was the precise measurement of a second not necessary for pastoral communities?

The precise measurement of a second was not necessary for pastoral communities because measuring days and hours was sufficient for their tasks.

Why did the need for precise timekeeping become important with the advent of railways?

Precise timekeeping became important with the advent of railways because cities needed to agree on exact timekeeping for the efficient functioning of the interconnected society.

What led to the development of atomic clocks in the 1950s?

The need for every second to be perfectly accounted for with as much precision as possible led to the development of atomic clocks in the 1950s.

How do atomic clocks achieve such high precision in timekeeping?

Atomic clocks achieve high precision by relying on the unchanging laws of physics and the consistent frequency of electrons orbiting an atom's nucleus.

What is the significance of the quantum spin in atomic clocks?

The quantum spin is significant in atomic clocks as it represents the orientation of the axis about which the electron rotates, making it easier to track the oscillation for timekeeping.

Why was cesium-133 chosen as the standard for timekeeping in 1967?

Cesium-133 was chosen because it met the criteria of having long-lived, high frequency electron oscillation, a reliably measurable quantum spin, a simple energy level structure, and being easy to vaporize.

How many ticks of a cesium-133 atom are there in one second?

There are exactly 9,192,631,770 ticks of a cesium-133 atom in one second.

What role do atomic clocks play in modern global positioning systems?

Atomic clocks play a crucial role in modern global positioning systems by providing a globally consistent time with unparalleled precision, which helps in synchronizing devices like radio signal transmitters and satellites.